Radioactivity — Paper 4 · IGCSE Physics 0625

131 10 (a) An iodine isotope 53 I decays by β-emission to an isotope of xenon (Xe). 131 (i) State the number of each type of particle in a neutral atom of 53 I. protons … neutrons … electrons … [2] (ii) State the symbol, in nuclide notation, for the xenon nucleus. … [2] (b) The background count rate of radioactivity in a laboratory is 30 counts / min. A radioactive sample has a half-life of 50 minutes. The sample is placed at a fixed distance from a detector. The detector measures an initial count rate from the sample, including background, of 310 counts / min. On Fig. 10.1, plot suitable points and draw a graph of the count rate from the sample, corrected for background, as it changes with time. 300 corrected count rate counts / min 200 100 0 0 20 40 60 80 100 120 140 160 time / min Fig. 10.1 [3] [Total: 7]

7 marks

Mark scheme: 10 (a) (i) Protons: 53 neutrons: 78 electrons: 53 B2 (ii) 13154Xe B1 B1 (b) Points plotted at 3 of: 0 s, 50 s, 100 s, 150 s B1 3 corrected counts/minute plotted at any from : (0, 280) (50, 140) (100, 70) (150, 35) M1 Graph drawn as curve through correct points A1 [Total: 7]

This question in 0625/42 Feb/March 2016

11 Bismuth-214 is radioactive. It has a half-life of 20 minutes. (a) The nuclide notation for bismuth-214 is Bi. State the composition of the nucleus of bismuth-214. … … [2] (b) Bismuth-214 decays by β-decay to an isotope of polonium, Po. Complete the equation for the decay of bismuth-214. → … 214Bi … β + … Po 83 [3] (c) The count rate from a sample of bismuth-214 is 360 counts/s. Predict the count rate from the sample after 60 minutes. count rate = … [2] (d) State two of the social, economic or environmental issues involved in the storage of radioactive materials with very long half-lives. … … … … [2] [Total: 9]

9 marks

Mark scheme: 11(a) 83 protons 131 neutrons B2 11(b) 0 1 −β Superscript 0 Subscript –1 214 84Po B1 B1 B1 11(c) (After 20 min count rate is) 360 / 2 or 180 (count / s) (After 40 min count rate is) 180 / 2 or 90 (counts / s) (After 60 min count rate is) 90 / 2 OR new count-rate = 360/(2 × 2 × 2) or 360 / 8 or 3 half-lives 45 (counts / s) C1 A1 Question Answer Mark 11(d) Any two points chosen from the lists below: (economic): high cost of storage / shielding / guarding / need to store for a long time OR reduction in tourism OR loss of farming produce / land OR reduction of land / property values (social): fear of cancer / causes cancer / genetic mutations / radiation sickness in people / animals OR local objections OR cause people to move away (environmental): crop mutations OR leakage into water supplies OR pollution of atmosphere / water supply B2 Total: 9

This question in 0625/41 May/June 2016

11 Radon-220 is a radioactive isotope. (a) The nuclide notation for radon-220 is Rn. Describe the composition of a neutral atom of radon-220. … … … … [3] (b) A nucleus of radon-220 decays to an isotope of polonium (Po) by emitting an alpha particle. Complete the nuclide equation for the decay of radon-220. → … 220Rn … α + … Po 86 [3] (c) A detector of radiation is placed near a sample of radon-220 and gives a reading of 720 counts/s. The half-life of radon-220 is 55s. Calculate the reading after 220s. Ignore background radiation. reading = … [2] [Total: 8]

8 marks

Mark scheme: 11(a) 86 protons (in nucleus) B1 134 neutrons (in nucleus) B1 86 electrons (surrounding nucleus / in orbit) B1 11(b) 4 2α B1 Po … 84 B1 Po 216 … B1 11(c) 220 / 55 or 4 (half-lives) or 720 / 16 C1 45 counts / s A1 Total: 8

This question in 0625/42 May/June 2016

10 A sample contains atoms of a particular isotope of protactinium . (a) A nucleus of this protactinium isotope contains 91 protons and 143 neutrons. (i) State the values of X and Y in the symbol . X = … Y = … [2] (ii) This isotope is radioactive and it decays by the emission of a β-particle, β, to an isotope of uranium, U. Complete the equation for the decay of a protactinium nucleus. … … 0 … Pa β + … U –1 [2] (b) A radiation detector measures a background count rate in a laboratory of 32 counts/minute. (i) Suggest two naturally occurring sources of background radiation. 1. … 2. … [2] (ii) The sample is placed in the laboratory close to the radiation detector, and the count rate increases to 544 counts/minute. This isotope of protactinium has a half-life of 400 minutes. Predict a value for the count rate measured 1200 minutes later. count rate = … [4] (iii) Suggest one reason why the count rate measured 1200 minutes later may differ slightly from the value predicted in (b)(ii). … … [1] [Total: 11]

11 marks

Mark scheme: 10(a)(i) (X = )234 B1 (Y = )91 B1 10(a)(ii) U (number 234 required in correct position) B1 U (number 92 required in correct position) B1 10(b)(i) any two lines from: rocks (buildings / earth / ground / wood / stone / minerals) space (Sun / stars / galaxies / cosmic rays) air (radon) B2 Question Answer Marks 10(b)(ii) 1200 ÷ 400 or 3 (half-lives) C1 544 – 32 or 512 or evidence of 3 halvings C1 1/8(th) or 64 or 68 C1 96 counts / minute A1 10(b)(iii) random fluctuations / variation B1 [Total: 80]

This question in 0625/43 May/June 2016

12 The nuclear equation below shows the decay of a plutonium (Pu) nucleus to an americium (Am) nucleus and a β-particle. β 241ZPu 24195Am + (a) (i) State the quantity that is represented by the letter Z in this equation. … [1] (ii) State the numerical value of Z. Z = … [1] (b) The americium nucleus decays by the emission of an α-particle into a neptunium (Np) nucleus. Complete the nuclear equation for this decay. 24195Am [2] (c) The half-life of this americium nuclide is 470 years. A sample of this nuclide contains 8.0 × 1014 atoms. After some time, 6.0 × 1014 americium atoms have decayed. Calculate the time required for this decay. time = … [3] [Total: 7]

7 marks

Mark scheme: 12(a)(i) Atomic number OR number of protons OR proton number B1 12(a)(ii) 94 B1 12(b) 237 93 Np + 4 2 α B1 B1 12(c) (No of Am atoms remaining = 8 × 1014 – 6 × 1014) = 2 × 1014 4 × 1014 (Am atoms remain after) 470 yrs or 1 half-life (2 × 1014 Am atoms remain after) 940 yrs or 2 half-lives C1 C1 A1 Total: 7

This question in 0625/41 Oct/Nov 2016

10 (a) The size of the charge on an electron is e. Since the charge on an electron is negative, it is written –e. Complete the table by writing down the charges, in terms of e, on the particles and radioactive emissions shown. particle charge proton neutron α-particle β-particle γ-ray [3] (b) Fig. 10.1 shows a radioactive source emitting α-particles, β-particles and γ-rays into a vacuum tube. N pole of vacuum strong magnet radioactive N source S block of lead with hole S pole of tube strong magnet Fig. 10.1 The block of lead ensures that the radiation is in a narrow beam when it passes between the poles of the magnet. State the direction of any deflection of (i) the α-particles, … … [1] (ii) the β-particles, … … [1] (iii) the γ-rays. … … [1] [Total: 6]

6 marks

Mark scheme: 10(a) proton (+)e neutron zero / neutral / no / none / nothing α-particle (+)2e β-particle – e γ-ray zero / neutral / no / none / nothing B3 10(b)(i) into page B1 10(b)(ii) clearly 180° from b i B1 10(b)(iii) none B1

This question in 0625/42 Oct/Nov 2016

11 A radioactive nuclide has a half-life of 4.0 days. A sample contains 9.6 × 108 atoms of the nuclide. (a) Calculate the number of atoms of the nuclide remaining after 12 days. number = … [2] (b) The count rate from the sample is measured in a laboratory where the background count rate is 16 counts / minute. A detector is placed at a fixed distance from the sample. The initial count rate measured by the detector is 160 counts / minute. Calculate the count rate measured by the detector after 12 days. count rate = … [2] [Total: 4]

4 marks

Mark scheme: 11(a) / 8 1.2 × 108 (atoms) C1 A1 11(b) 160 – 16 OR 144 (144 / 8 + 16 = 18 + 16 =) 34 counts / minute C1 A1

This question in 0625/42 Oct/Nov 2016

11 A radioactive source is placed 20 mm from a radiation detector, as shown in Fig. 11.1. lead source narrow beam detector of radiation 20 mm Fig. 11.1 (not to scale) The initial count rate recorded by the detector is 150 counts / s. A sheet of paper is placed between the source and the detector. The count rate recorded by the detector falls to 60 counts / s. With the paper still in place, a magnetic field is set up perpendicular to the direction of the radiation. The count rate recorded by the detector falls to 20 counts / s. The count rates have not been corrected for background. The background count is measured as 20 counts / s. (a) State the evidence that each type of radiation is present in, or absent from, the radiation emitted by the source. α-particles … … β-particles … … γ-rays … … [5] (b) Determine how much of the original count rate of 150 counts / s, if any, is due to each type of radiation. α-particles … counts / s β-particles … counts / s γ-rays … counts / s [2] [Total: 7]

7 marks

Mark scheme: 11(a) B1 α-particles: stopped by / absorbed by paper B1 β-particles: deflected by (magnetic) field B1 γ-rays: absent B1 with paper and magnetic field count falls to background / 20 counts / s. B1 11(b) α-particles: (150 – 60 =) 90 counts / s β-particles: (60 – 20 =) 40 counts / s γ-rays: zero All 3 correct = 2 marks; 1 or 2 correct = 1 mark. B2 Total: 7

This question in 0625/42 Feb/March 2017

11 (a) A radioactive source is tested over a number of hours with a radiation detector. The readings are shown in Table 11.1. Table 11.1 time / hours 0 1 2 3 4 5 6 7 8 9 10 detector reading / (counts / s) 324 96 39 23 21 17 21 20 19 20 18 Use the readings to suggest a value for the background count rate during the test, and to determine the half-life of the sample. background count rate = … half-life of sample = … [4] (b) Hydrogen-3 (tritium) has one proton and two neutrons. The nucleon number of tritium is three. It decays by emitting a β-particle. Complete the nuclide equation to show this decay. The symbol X represents the nuclide produced by this decay. … … … … … … H β + X [3] (c) The arrows in Fig. 11.1 show the paths of three α-particles moving towards gold nuclei in a thin foil. gold nucleus gold nucleus gold nucleus Fig. 11.1 On Fig. 11.1, complete the paths of the three α-particles. [3] [Total: 10]

10 marks

Mark scheme: 11(a) Background count rate stated as in range 17 – 21 counts / s B1 Background used on at least 2 of first 3 readings C1 Any halving of corrected or uncorrected reading C1 (half-life =) ½ hour A1 11(b) 3 1 H on LHS of an equation B1 0 -1 β on RHS of equation B1 Equation all correct: 3 1 H = 0 -1 β + 3 2 X B1 11(c) Top: any path to the left within 45° horizontal B1 Middle: path to the right and deflected down (ending in a straight line) B1 Bottom: path not deflected OR path to the right and deflected up much less than middle path B1 Total: 10

This question in 0625/41 May/June 2017

11 (a) The arrows in Fig. 11.1 represent the paths of three α-particles moving towards gold nuclei in a thin foil. The gold nuclei are shown as shaded circles. Fig. 11.1 On Fig. 11.1, complete the paths of the three α-particles. [3] (b) Fig. 11.2 shows a geologist holding a radiation detector near a rock. radiation detector rock Fig. 11.2 She holds the detector in a fixed position and records the readings shown in Table 11.1. Table 11.1 time / minutes 0 1 2 3 4 5 detector reading 16 14 17 13 17 15 counts / minute Explain the changes in the detector readings. … … … … [2] (c) A technician is handling a solid radioactive sample that emits α-particles and β-particles. The technician wears thick rubber gloves. Explain why this may provide some protection from the radiation, but it is not sufficient protection. … … … … [2] [Total: 7]

7 marks

Mark scheme: 11(a) (so insufficient protection) B1 middle: any path to the left within 45° of horizontal B1 bottom: path to the right and deflected down ending in a straight line B1 11(b) radiation from background/rock/air/outer space/cosmic rays B1 random variation owtte. B1 11(c) thick gloves would stop α/alpha (so helpful) B1 (some) β/beta/radiation would penetrate gloves/reach other body parts (so insufficient protection) B1 Total: 7

This question in 0625/42 May/June 2017

11 (a) Fig. 11.1 shows equipment that is used to investigate the effect of a magnetic field on the path of a beam of γ-rays. thick lead plates beam of γ-rays γ-ray detector source of γ-rays Fig. 11.1 A radioactive source emits γ-rays. The γ-rays pass through two small holes in thick lead plates. Then the γ-rays pass through the shaded region and into the detector. (i) Suggest the purpose of the two lead plates. … … [1] (ii) A magnetic field, directed into the page, is set up in the shaded region. State and explain what happens to the reading of the detector. … … … … [3] (b) State the relative ionising effects of α-particles, β-particles and γ-rays. Suggest an explanation for the differences. … … … … [3] [Total: 7]

7 marks

Mark scheme: 11(a)(i) B1 11(a)(ii) no change B1 γ-rays not deflected B1 γ-rays are electromagnetic radiation/uncharged OR not deflected by magnetic field B1 11(b) (ionising effect of) α-particles greater than β-particles and β-particles greater than γ-rays B1 any two from: mass α > mass β > mass γ charge α > charge β > charge γ speed γ > speed β > speed α B2 Total: 7

This question in 0625/43 May/June 2017

11 The radioactive isotope carbon-14 (146 C) emits β-particles as it decays. (a) The decay of carbon-14 produces an isotope of nitrogen (N). (i) State the nature of a β-particle and state where it is produced. … … [2] (ii) Complete the nuclide equation for the radioactive decay of carbon-14. 14 … … C + [3] 6 … N … β (b) The half-life of carbon-14 is 5700 years. Explain what is meant by the term half-life. … … [1] (c) A workman operates a machine that uses β-particles to determine the level of liquid in a plastic water bottle that is being filled. Suggest why (i) α-particles are not suitable for the same purpose, … … [1] (ii) γ-rays are not suitable for the same purpose. … … [1] [Total: 8]

8 marks

Mark scheme: 11(a)(i) An electron M1 In / from / by the nucleus A1 11(a)(ii) Proton numbers balance on left and right sides of equation B1 Nucleons numbers balance on left and right sides of equation B1 0 1 −β B1 11(b) Time for activity / count rate / number of nuclei / number of atoms to halve B1 11(c)(i) α-particles would be stopped / absorbed by the plastic / bottle B1 11(c)(ii) γ-rays would not be absorbed by the liquid / bottle OR reading not reduced (in passing through liquid / bottle) OR very penetrative so no change in detector reading B1

This question in 0625/41 Oct/Nov 2017

11 The radioactive isotope bismuth-210 (21083 Bi) decays by β-particle emission to an isotope of polonium (Po). (a) Complete the nuclide equation that represents this decay. 210 … … Bi + 83 … Po … β [3] (b) A radiation detector is placed on a bench in a laboratory where there are no artificial sources of radiation. The detector is switched on. In seven one-minute periods, the detector displays these readings. 24 22 25 25 21 20 24 (i) Explain why, in the absence of any artificial source, there are readings on the detector. Suggest one origin of this effect. … … … [2] (ii) Explain why the readings obtained are not all the same. … … [1] (iii) The half-life of bismuth-210 is 5.0 days. A sample of bismuth-210 is brought close to the detector and in one minute, the reading displayed is 487. The equipment is left in the same place for exactly 10 days. Predict the reading in a one-minute period at the end of this time. reading = … [3] [Total: 9]

9 marks

Mark scheme: 11(a) nucleon numbers balance each side of equation B1 proton numbers balance each side of equation B1 0 1 −β B1 11(b)(i) background radiation OR radiation from the environment B1 rocks / ground / buildings / food / space / weapons testing / nuclear accidents or waste / sun / air / radon / argon B1 11(b)(ii) random (variation) B1 11(b)(iii) clear evidence of subtracting 23 from (original) count C1 clear evidence of dividing original / corrected count by 4 A1 clear evidence of adding 23 correctly to result after division A1

This question in 0625/42 Oct/Nov 2017

10 (a) State the nature of γ-rays. … … [2] (b) A nucleus of technetium-99 (9943Tc) emits only a γ-ray. State any effect of this on (i) the proton number of the nucleus, … [1] (ii) the nucleon number of the nucleus. … [1] (c) In a laboratory a radiation detector displays a count rate of 16 counts / minute due to background radiation. (i) State what is meant by background radiation. … … [1] (ii) A sample of a radioactive isotope is placed near to the radiation detector and a count rate of 112 counts / minute is recorded. After 18 hours, the count rate recorded is 28 counts / minute. Determine the half-life of this isotope. half-life = … [3] (d) Radioactive isotopes are stored in thick lead containers. State two precautions to be taken when radioactive isotopes are used. 1. … 2. … [2] [Total: 10]

10 marks

Mark scheme: 10(a) electromagnetic (waves / rays / radiation) M1 high frequency / energy or short wavelength A1 10(b)(i) no change or (stays at) 43 B1 10(b)(ii) no change or (stays at) 99 B1 10(c)(i) (radiation) always present / due to environment / in absence of radioactive sample / natural (radiation) B1 10(c)(ii) 112 – 16 or 96 or 112 / 28 or ¼ or 18 / 2 C1 28 – 16 or 12 or 1 / 8 or 18 / 3 or 9.0 (hours) C1 6.0 hours A1 10(d) any two of: • (distance): tongs / manipulator / centre of cardboard box • (absorption): lead gloves / suit / lead glass screen / googles / glasses • (time): limit exposure time / keep in box until needed / film badge B2

This question in 0625/43 Oct/Nov 2017

11 Radon-222 is radioactive. It can be represented as 22286 Rn. (a) For a neutral atom of radon-222, state 1. the number of protons, … 2. the number of neutrons, … 3. the number of electrons. … [2] (b) A radon-222 nucleus decays by α-particle emission to a polonium (Po) nucleus. Complete the equation for the decay of radon-222. 222 Rn [2] 86 (c) Radon-222 has a half-life of 3.8 days. At a certain time, a sample contains 6.4 × 106 radon nuclei. Calculate the number of α-particles emitted by the radon nuclei in the following 7.6 days. number = … [3] [Total: 7]

7 marks

Mark scheme: 11(a) Number of protons = 86 and number of electrons = 86 1 Number of neutrons = 136 1 11(b) 218 84 Po 1 + 4 2 α 1 11(c) 7.6 days = 2 half-lives or evidence of two halvings 1 (number of Rn atoms left = 6.4 × 106 ÷ 4 =) 1.6 × 106 1 number of α-particles emitted = (6.4 × 106 – 1.6 × 106 =) 4.8 × 106 1

This question in 0625/41 May/June 2018

6 (a) Circle two of the following that apply to an ultrasound wave travelling in air. frequency 3.5 Hz frequency 350 Hz frequency 35 000 Hz longitudinal transverse speed 1.5 m / s speed 1.5 × 103 m / s speed 1.5 × 106 m / s [2] (b) Calculate the wavelength in a vacuum of X-rays of frequency 1.3 × 1017 Hz. wavelength = … [3] (c) A dentist takes an X-ray photograph of a patient’s teeth. Explain why it is safe for the patient to be close to the source of X-rays, but the dentist must stand away from the source. … … … … [2] (d) State, with a reason, why microwave ovens are designed only to work with the door closed. … … … [2] [Total: 9]

9 marks

Mark scheme: 6(a) frequency 35 000 Hz ringed 1 longitudinal ringed 1 6(b) v = f λ OR (λ = ) v ÷ f 1 (λ=) 3 × 108 ÷ 1.3 × 1017 1 (λ =) 2.3 × 10–9 m 1 6(c) X-rays ionising/harmful/dangerous (to humans) 1 Any one from: patient rarely exposed low total dose on patient meaningful comment about benefit outweighs danger dentist frequently exposed total dose on dentist would be high if stayed in room 1 6(d) microwaves harmful/dangerous (to humans) 1 microwaves would pass through open door 1

This question in 0625/42 May/June 2018

11 (a) A radioactive nucleus of uranium-235 decays to a nucleus of thorium and emits an α-particle. Complete the equation. 235 … U Th + 4 α 92 … 2 [2] (b) A nucleus of uranium-235 undergoes nuclear fission in a reactor. (i) State what is meant by nuclear fission. … … … [1] (ii) Suggest why a nuclear reactor is surrounded by thick concrete walls. … … … … [2] (iii) State one environmental advantage and one environmental disadvantage of using a fission reactor to generate electrical energy in a power station. advantage … … disadvantage … … [2] (c) The thorium produced by the decay in (a) is also radioactive and has a half-life of 26 hours. At a certain time, a pure sample of this isotope initially contains 4.8 × 109 atoms. Calculate the number of atoms of this sample that decay in the following 52 hours. number = … [3] [Total: 10]

10 marks

Mark scheme: 11(a) 1 90Th 1 11(b)(i) splitting of a nucleus into (2) parts/light(er)nucleus 1 11(b)(ii) (fission involves production of) ionising radiation OR radiation dangerous/harmful (to humans) 1 (thick concrete walls) absorb/stop the radiation (and so protect workers) 1 11(b)(iii) no CO2/SO2/greenhouse gases/acid rain 1 nuclear waste (disposal) OR leaks of radioactive material OR risk of radiation in case of accident 1 11(c) (52 hours =) 2 half-lives OR evidence of 2 halvings 1 (after 52 hours number of thorium atoms left = 4.8 × 109 ÷ 4 =) 1.2 × 109 OR (number of thorium atoms decayed =) ¾ × 4.8 × 109 1 (number of atoms decayed = 4.8 × 109 – 1.2 × 109 ) = 3.6 × 109 1

This question in 0625/42 May/June 2018

11 (a) State the type of radioactive emission that causes (i) the proton number of a nuclide to increase by 1, … [1] (ii) the nucleon number of a nuclide to decrease by 4, … [1] (iii) no change in the proton number and no change in the nucleon number of a nuclide. … [1] (b) The isotope radon-220 is radioactive and it decays by α-particle emission. (i) Fig. 11.1 shows a beam of α-particles entering the electric field between two charged plates. charged plate + + + + + + + + + + electric field beam of α-particles – – – – – – – – – – charged plate Fig. 11.1 On Fig. 11.1, sketch the path that the beam of α-particles follows in the electric field. [1] (ii) The half-life of radon-220 is 56 s. A sample of this isotope contains 7.2 × 106 atoms. Predict the number of α-particles that the radon-220 in the sample emits in the next 168 s. number of α-particles emitted = … [3]

7 marks

Mark scheme: 11(a)(i) B1 11(a)(ii) α(-particles) B1 11(a)(iii) γ(-rays) B1 11(b)(i) downward curve B1 11(b)(ii) 3 (half-lives identified) OR 168 ÷ 56 C1 1 ÷ 8 OR 9.0 × 105 (Rn) atoms remain C1 (7.2 × 06 – 9.0 × 105 =) 6.3 × 106 (α-particles emitted) A1

This question in 0625/43 May/June 2018

11 (a) Fig. 11.1 shows data about nine elements. proton number element symbol 2 helium He 3 lithium Li 4 beryllium Be 5 boron B 6 carbon C 7 nitrogen N 8 oxygen O 9 fluorine F 10 neon Ne Fig. 11.1 Carbon-14 is a radioactive isotope with a nucleon number of 14. It decays by emitting β-particles. Use any data you need from Fig. 11.1 to write down the nuclide equation for this decay. [4] (b) A radioactive sample is placed close to a detector. The radioactive isotope in the sample has a long half-life. The detector records a count rate of 597 counts / s. Fig. 11.2 shows the readings when different materials are placed between the radioactive sample and the detector. count rate material counts / s a sheet of paper 602 a piece of thin aluminium 598 a piece of thin lead 510 Fig. 11.2 Explain whether any α-particles, β-particles or γ-rays are emitted by the radioactive sample. α-particles … … β-particles … … γ-rays … … [3] [Total: 7]

7 marks

Mark scheme: 11(a) 14 6 C on left-hand side B1 14 7 on right-hand side (ignoring letter after or before 14 7 ) B1 N after 14 7 on right-hand side B1 + 0 1 − e on right-hand side OR – 0 1 − e on left-hand side B1 11(b) Not α because count-rate with paper increase B1 Not β because count-rate with aluminium increase B1 is γ because count rate reduces with lead only OR does not reduce with paper or aluminium B1

This question in 0625/41 Oct/Nov 2018

10 (a) A detector of ionising radiation measures the background count rate in a classroom where there are no radioactive samples present. The readings, in counts/minute, taken over a period of time are shown in Table 10.1. Table 10.1 counts / minute 16 12 14 16 15 17 (i) State two possible sources of this background radiation. … … [2] (ii) Explain why the readings are not the same. … … [1] (b) With no radioactive sample present, a scientist records a background radiation count of 40 counts / minute. He brings a radioactive sample close to the detector. The count rate increases to 200 counts / minute. After 24 days the count rate is 50 counts / minute. Calculate the half-life of the radioactive sample. half-life = … [4] (c) Draw a line between each type of ionising radiation and its property and another line between the property and its use. One has been done for you. Name of Property Use ionising radiation It is the most ionising radiation Remotely detecting and is most easily X-ray leaks in underground absorbed by very water pipes small amounts of substance Penetration is affected by small Detecting fractures in α-particle changes in the bones amount of solid it is passing through It is highly Detecting smoke in a β-particle penetrating and is fire alarm system poorly ionising Can pass easily Detecting a change in through soft living the thickness of γ-ray tissue. Calcium aluminium foil during absorbs more than its manufacture soft tissue [3] [Total: 10]

10 marks

Mark scheme: 10(a)(i) any two from • soil / rocks / buildings / the Earth • cosmic rays / space • the Sun • medical sources • food or drink • air / radon B2 10(a)(ii) random (variation of background radiation / radioactivity) B1 10(b) 160 and 10 (counts / min) C1 (160 / 10= ) 16 C1 4 half-lives A1 (24 / 4 = ) 6 days B1 10(c) 2 correct lines B1 4 correct lines B1 6 correct lines B1

This question in 0625/42 Oct/Nov 2018

10 Thorium-234 (23940Th) is radioactive. It decays by β-emission to form an isotope of protactinium (Pa). (a) Complete the nuclide equation for this decay. … … 23 4 … Pa + … β 9 0Th [2] (b) A pure sample of thorium-234 emits β-particles at a count rate of 2480 counts / second. The half-life of thorium-234 is 24 days. Calculate the count rate for the emission of β-particles from the thorium in the sample after 72 days have passed. count rate … [3] (c) The isotope of protactinium in (a) is also radioactive. It decays by β-emission and has a half-life of 70 seconds. State and explain how this would affect the observed count rate for the sample in (b) after 72 days. … … … … [3] [Total: 8]

8 marks

Mark scheme: 10(a) ( ) 234 91 Pa B1 ( ) 0 –1 β B1 10(b) 72 / 24 or 3.0 (half-lives) C1 23 or 1 / 8 or 2480 / 8 C1 310 counts / second A1 10(c) count rate larger (than 310 counts / second) B1 protactinium is also emitting (β-)particles / (nuclear) radiation B1 count rate (approximately) double or product of protactinium decay also radioactive or amount of protactinium small or protactinium is highly radioactive or half-life of protactinium much shorter (than half-life of thorium) / very short B1

This question in 0625/43 Oct/Nov 2018

11 (a) (i) One isotope of iridium-194 is represented by 194 Ir 77 This isotope decays by β-emission to a stable isotope of platinum (Pt). Complete the nuclide equation for this decay. 194 Ir … Pt + … β 77 … … [3] (ii) The half-life of iridium-194 is 19 hours. A sample of iridium-194 has an initial count-rate of 1100 counts / min. Calculate the count-rate from this sample after 38 hours. count-rate = … [2] (b) State two ways in which γ-emission differs from β-emission. 1 … 2 … [2] [Total: 7]

7 marks

Mark scheme: 11(a)(i) Nucleon number for Pt: 194 B1 Proton number for Pt: 78 B1 Symbol for beta particle: 0 1 − β B1 11(a)(ii) After 1 half-life / 19 hrs, count rate = 1100 / 2 = 550 counts / min C1 After 2 half-lives / 38 hrs, count rate = 550 / 2 = 275 counts / min A1 OR 38 hrs = 2 half-lives (C1) After 38 hrs / 2 half-lives, count rate = 1100 / 4 = 275 counts / min (A1) Question Answer Marks 11(b) Two of: γ-emission β-emission electromagnetic radiation / travels at the speed of light particles / electrons uncharged (negatively) charged no mass has mass long range in air shorter range in air stopped by many cm of lead / very penetrating stopped by a few mm of aluminium low ionisation (of air) higher ionisation (of air) leaves proton number unchanged proton number changes not deflected in electric / magnetic field deflected in electric / magnetic field B2

This question in 0625/42 Feb/March 2019

9 (a) Fig. 9.1 shows a beam of α-particles moving towards a thin sheet of gold in a vacuum. gold sheet beam of α-particles detectors vacuum Fig. 9.1 Detectors in the region surrounding the thin gold sheet detect the α-particles and determine the number of particles that travel in various directions. State and explain what can be deduced from the following observations. (i) The majority of the α-particles pass through the gold sheet undeflected and are detected on the far side. deduction … explanation … … [2] (ii) A small number of α-particles are deflected as they pass through the gold sheet. deduction … explanation … … [2] (iii) A very small number of α-particles are deflected through very large angles or return back the way they came. deduction … explanation … … [2] (b) A beam that consists of both α-particles and β-particles is passed through a region of space where there is a magnetic field perpendicular to the direction of the beam. State two ways in which the deflection of the α-particles differs from that of the β-particles. 1. … 2. … [2] [Total: 8]

8 marks

Mark scheme: 9(a)(i) mark both explanation and deduction together nucleus is very small B1 very few α-particles hit or pass near to a nucleus B1 9(a)(ii) mark both explanation and deduction together nucleus is charged B1 (charged) α-particles experience a force B1 9(a)(iii) mark both explanation and deduction together centre / (small) part of atom OR nucleus includes most of the mass of the atom / is (very) dense B1 (α-particles move and) nucleus stays still B1 9(b) any two from: opposite direction (much) smaller deflection undergo deflections of similar magnitude B2

This question in 0625/41 May/June 2019

11 (a) A radon-222 nucleus contains 86 protons and 136 neutrons. It decays by emitting an α-particle and becomes a nucleus of an isotope of polonium. The symbol for radon is Rn and the symbol for polonium is Po. Write down the nuclide equation for this decay. [3] (b) Carbon-14 is radioactive with a half-life of 5700 years. An animal bone is dug up in an archaeological excavation. The quantity of carbon-14 in the bone is 25% of what it was when the bone was buried. Calculate the time that has elapsed since it was buried. time = … years [2] [Total: 5]

5 marks

Mark scheme: 11(a) 222 86Rn on L side of equation B1 218 84Po on R side of equation B1 4 2α on R side of equation B1 11(b) mention of 2 half-lives OR mention or use of two halvings of 100% NOT 5700 ÷ 2 OR 14 ÷ 2 C1 11 000 (years) A1

This question in 0625/42 May/June 2019

11 (a) Americium (Am) is a radioactive isotope. A nucleus of americium contains 95 protons and 146 neutrons. It decays by emitting an α‑particle to form a nucleus of an isotope of neptunium (Np). Write down the nuclide equation for the decay of americium to neptunium. [4] (b) Ionisation smoke detectors contain americium and two small electrodes with a small voltage between them. The air between the electrodes is ionised by α‑particles so that there is a small electric current between the electrodes. (i) Suggest and explain the effect of smoke on the current between the electrodes in the smoke detector. Suggestion: … … Explanation: … … [1] (ii) Suggest two reasons for using an α‑particle emitter in a smoke detector. Reason 1 … … Reason 2 … … [2] [Total: 7]

7 marks

Mark scheme: 11(a) 241 95Am →4 2α + 237 93Np Am on L with correct proton no B1 Am on L with correct nucleon no B1 alpha symbol on R with correct proton and nucleon no B1 Np on R with correct proton and nucleon no. B1 11(b)(i) current decreases / is stopped AND alpha particles absorbed (by smoke) owtte B1 11(b)(ii) Any two from: alpha particles highly ionizing / more ionising than beta particles or gamma rays alpha particles short range (in air) safer to use alpha because they do not travel out of smoke detector B2

This question in 0625/43 May/June 2019

9 (a) The chemical symbol of the element lithium is Li. The proton number of lithium is 3. Fig. 9.1 is a representation of a nucleus of a radioactive isotope of lithium that is about to decay. Fig. 9.1 (i) Write down, using nuclide notation, the symbol that represents this isotope of lithium. … [1] (ii) This isotope of lithium decays by β-particle emission to form another nucleus. Complete Fig. 9.2 to represent this decay by: • using the same representation as in Fig. 9.1 and in the space after the arrow, draw a diagram of the nucleus formed by the decay • writing the name of the particle that is identical to a β-particle on the answer line provided. + … Fig. 9.2 [3] (b) A radiation detector is set up in a laboratory where there are no radioactive samples. On six separate occasions, the detector is switched on for 1.0 minute and the background count is recorded. The counts are: 23 27 25 24 20 25 (i) State why the readings are not all identical. … [1] (ii) Suggest a possible source for this background radiation. … [1] (iii) A sample containing only one radioactive isotope is brought into the laboratory. The half-life of the isotope is 15 hours. The sample is placed near to the radiation detector in this laboratory. The detector is switched on and, after 1.0 minute, a count of 440 is recorded. The sample is left next to the detector and the experiment is repeated 45 hours later. The detector is switched on for 1.0 minute. Predict the reading for the count obtained on this occasion. reading … [3] [Total: 9]

9 marks

Mark scheme: 9(a)(i) (Li) 3 B1 9(a)(ii) 4 × 4 × electron B1 B1 B1 9(b)(i) radioactive emission / (background) radiation / decay is random B1 9(b)(ii) any one of: rocks, buildings, soil, Earth, space, cosmic rays, Sun, radon, nuclear waste, weapons testing B1 9(b)(iii) 440 – 24 or 416 or 52 or 55 or 79 or 3 (half-lives) or 45 / 15 or 1 / 23 or 1 / 8 1/23 or 1/8 or 52 or 55 or 79 76 (counts) C1 C1 A1

This question in 0625/41 Oct/Nov 2019

10 (a) The nucleus of a hydrogen atom is a proton. The mass of a proton is m and the size of the charge on a proton is e. Complete Table 10.1. Express your answers in terms of m and e. Three spaces have already been completed. Table 10.1 particle or emission mass charge proton m e neutron m γ-ray nucleus of helium-4 (42He) [4] (b) Many schools and colleges use radioactive isotopes for teaching and research. Describe how these radioactive isotopes are handled, used and stored in a safe way. … … … … … … [3] [Total: 7]

7 marks

Mark scheme: 10(a) neutron charge = 0 γ-ray mass = 0 AND charge = 0 He nucleus mass = 4 m He nucleus charge = 2 e B1 B1 B1 B1 10(b) any 3 different valid points, e.g. • detail of handling source appropriately for, e.g. use of tongs • protective clothing • minimise exposure by time OR distance OR activity • detail of shielded storage • detail of secure storage • monitoring exposure • must be disposed of securely • limitation of access to approved personnel • procedure in place in case of accident / criminal act to protect people and / or environment 3 × B1

This question in 0625/42 Oct/Nov 2019

11 (a) The circles shown in Fig. 11.1 represent three gold nuclei. Three α-particles are approaching the gold nuclei. α-particle α-particle α-particle Fig. 11.1 On Fig. 11.1, complete the path of each α-particle. [3] (b) A detector of radioactivity in a laboratory indicates an average of 16 counts / min when no radioactive samples are present. A radioactive sample of half-life 1.5 days is placed close to the detector, which indicates a count rate of 208 counts / min. Calculate the count rate that is indicated 6 days later. count rate = … counts / min [4] (c) The waste from nuclear power stations includes the isotopes technetium-99, tin-126 and selenium-79. These isotopes are radioactive with half-lives of many thousands of years. State three economic and environmental consequences of producing this waste. … … … … … … … [3] [Total: 10]

10 marks

Mark scheme: 11(a) top: any path to the left within 45 degrees to the horizontal B1 middle: path to the right and deflected up (ending in a straight line) B1 bottom: path to the right and deflected down (ending in a straight line) B1 11(b) 192 B1 use or clear indication of 4 half-lives C1 (192 / 16 =) 12 A1 28 B1 11(c) any 3 different valid points e.g. • must be stored with shielding • must be stored securely / safely • must be transported with shielding • must be transported securely • expensive to store • expensive to transport • in case of accident / terrorism could escape to environment / danger to people • site of storage uninhabitable for thousands of years 3 x B1

This question in 0625/43 Oct/Nov 2019

11 (a) The isotope hydrogen-1 has a proton number of 1 and a nucleon number of 1. Two isotopes of helium are helium-3 and helium-4. Helium-3 has a proton number of 2 and a nucleon number of 3. Helium-4 has a nucleon number of 4. Complete Table 11.1 for neutral atoms of these isotopes of helium. Table 11.1 helium-3 helium-4 number of neutrons number of electrons mass compared to a neutral atom of hydrogen-1 [3] (b) An experiment takes place in a laboratory shielded from all background radiation. A sample of radioactive material is wrapped in aluminium foil of thickness 0.1 mm. A detector of ionising radiation placed 1 cm from the foil records a reading. A piece of aluminium of thickness 5 mm is placed between the detector and the foil. The detector reading drops to zero. State and explain any type of radiation passing through the aluminium foil. … … … … [3] [Total: 6]

6 marks

Mark scheme: 11(a) neutrons 1 2 B1 electrons 2 2 B1 mass 3 4 OR 2 more 3 more B1 11(b) β B1 β – (would be) stopped by 5 mm / thick Al B1 α – (would be) stopped by 0.1 mm Al / Al foil AND γ – (would) not (be) stopped by 5 mm / thick Al B1

This question in 0625/42 Feb/March 2020

10 Fig. 10.1 represents a neutral atom of an isotope of element X. Fig. 10.1 (a) State one similarity between this atom and a neutral atom of a different isotope of element X. … … [1] (b) The isotope of element X is radioactive. It decays to form an isotope of element Y by emitting a β-particle. (i) Using Fig. 10.1 deduce the nuclide notation for the isotope of Y produced by this decay. … nuclide notation: [3] … Y (ii) β-particles ionise the air they pass through less strongly than the same number of α-particles. Suggest why this is so. … … … [3] [Total: 7]

7 marks

Mark scheme: 10(a) equal number of electrons OR equal number of protons B1 10(b)(i) 13 5 X C1 0 1β − C1 13 6Y A1 10(b)(ii) any three from: • β-particles have charge of smaller size • β-particles have smaller mass • β-particles have less energy • β-particles travel faster / less time near to air molecule • effect / force on electrons in air molecules less B3

This question in 0625/41 May/June 2020

10 Fig. 10.1 shows a vacuum tube with a radioactive source. The radioactive source emits α-particles, β-particles and γ -rays. There is a very strong magnetic field between the N pole and the S pole of the magnet. lead cylinder with narrow vacuum central hole radioactive source N S α-particles, β-particles and γ-rays Fig. 10.1 (a) The lead cylinder has a narrow central hole. State and explain the effect of the lead cylinder. … … [2] (b) Describe the paths of the α-particles, β-particles and γ -rays as they pass through the magnetic field. Explain your answers. (i) α-particles … … … [2] (ii) β-particles … … … … [2] (iii) γ -rays … … … [2] [Total: 8]

8 marks

Mark scheme: 10(a) (beam) narrow OR straight OR in one direction owtte B1 radiation in other directions absorbed B1 10(b)(i) out of page / towards viewer B1 equiv. to current in direction of beam B1 10(b)(ii) opposite to (i) B1 equiv. to current in opposite direction to beam OR LH rule mentioned or described B1 10(b)(iii) none B1 (γ) uncharged OR not equivalent to current B1

This question in 0625/42 May/June 2020

10 (a) A radioactive nucleus of carbon decays to a nucleus of nitrogen by emitting a particle. Complete the nuclide equation and state the name of the particle. 14 C 14 N + … X 6 7 … name of particle X …………………………………………….. [3] (b) A radiation detector in a laboratory records a reading of 10 counts / min. There are no radioactive samples in the laboratory. (i) Explain why the radiation detector records a reading and suggest a possible source. explanation … source … … [2] (ii) Carbon-14 has a half-life of 5700 years. There are atoms of carbon-14 in all living organisms. An archaeologist digs up some ancient wood. In the same laboratory as in (b)(i), a sample of this ancient wood gives a reading of 20 counts / min. An equivalent sample of living wood gives a reading of 80 counts / min. It is suggested that the age of the ancient sample is 11 400 years. Do a calculation to check whether this suggestion is correct. [4] [Total: 9]

9 marks

Mark scheme: 10(a) 0 X -1 X B1 β OR beta (particle) B1 10(b)(i) background radiation B1 rocks / ground / buildings / food / space / weapons testing / nuclear accidents or waste / sun / air / radon / argon B1 10(b)(ii) subtracts 10 from 80 B1 evidence of recognising two half-lives OR compares 70 and 10 B1 (final reading =) 70/4 + 10 = 27 OR (70/10 = 7) age > 2 half-lives OR age nearly 3 half-lives B1 age > 11 400 B1

This question in 0625/43 May/June 2020

7 (a) A permanent magnet is made from only one material. Underline the material from which it is possible to make a permanent magnet. [1] aluminium copper soft iron mercury plastic steel uranium (b) An electron source produces a narrow beam of electrons that all travel at the same speed. The electron source is placed in a vacuum and the beam of electrons travels vertically downwards. Fig. 7.1 shows the beam of electrons before it passes between the N-pole and the S-pole of a magnet. electron source beam of electrons N-pole S-pole Fig. 7.1 (i) Describe what is meant by the direction of a magnetic field. State the direction of the magnetic field between the two poles in Fig. 7.1. … … … [1] (ii) Describe and explain what happens to the beam of electrons in the magnetic field between the poles of the magnet in Fig. 7.1. … … … … [3] (c) A beam consists of α-particles, β-particles and γ-rays. Explain how a uniform magnetic field may be used to separate the α-particles, the β-particles and the γ-rays. … … … … [3] [Total: 8]

8 marks

Mark scheme: 7(a) steel (underlined) B1 7(b)(i) the direction of the force on a N-pole and left to right / N to S B1 7(b)(ii) beam deflects B1 beam deflects into the page B1 moving electrons / charges constitute a current or left-hand rule or moving electrons / current in a magnetic field experiences a force B1 7(b) (part of) beam deflects B1 α-particles deflect in opposite / different direction to β-particles / electrons or all α-particles have similar deflections or α- particles deflect less B1 γ-rays do not deflect B1

This question in 0625/41 Oct/Nov 2020

10 A radiation detector is placed on the bench in a laboratory. It detects a background count rate of 40 counts / minute. (a) State what is meant by background radiation. Suggest one source for it. … … … [2] (b) A sample containing atoms of the radioactive isotope polonium-208 is removed from a lead container and brought close to the detector. The average count rate increases to 890 counts / minute. When two sheets of paper are inserted between the sample and the detector, the average count rate returns to 40 counts / minute. Polonium-208 is represented by the symbol 20884Po. It decays to an isotope of lead (Pb). (i) Deduce the type of radiation emitted by polonium-208. Explain your answer. … … … … [2] (ii) Write down the nuclide equation for the decay of polonium-208. [3] [Total: 7]

7 marks

Mark scheme: 10(a) radiation that is always present or due to environment or in everyday life B1 soil / rocks / earth / cosmic rays / space / Sun / weapons testing / radon / nuclear waste B1 10(b)(i) alpha-emission (only) B1 alpha-particles do not penetrate (two sheets of) paper or β-particles and γ-rays pass through (two sheets of) paper B1 10(b)(ii) Po ଼ସ ଶ଴଼ → ߙ ଶ ସ / He ଶ ସ B1 204Pb... or 82Pb C1 204 82Pb A1

This question in 0625/41 Oct/Nov 2020

11 (a) State two differences between nuclear fission and nuclear fusion. 1 … … 2 … … [2] (b) Radioactive tracers emitting γ-rays can be used in medicine. The half-life of the source of these γ-rays is 6 hours. (i) Explain why a source of γ-rays used in this way should not have a half-life shorter or longer than about 6 hours. … … … … [2] (ii) Technetium-99 is a source of γ-rays often used as a radioactive tracer. It is produced from molybdenum-99 which emits β-particles. The symbol for technetium is Tc and the symbol for molybdenum is Mo. Complete the nuclide equation for this decay. … … 99 Mo Tc + β 42 … … [3] (iii) Technetium-99 is a radioactive nuclide. State another use of radioactive nuclides in medicine. … … [1] [Total: 8]

8 marks

Mark scheme: 11(a) nuclear fission – nucleus / atom splits (into two) AND nuclear fusion – two nuclei / atoms join together B1 One from • {nuclear fission –large(r) mass (number) OR heavy nuclei / atoms involved OR neutrons involved / emitted} AND nuclear fusion – small(er) mass (number) OR light nuclei / atoms involved OR no neutrons • fission in a nuclear reactor AND fusion in Sun / stars • fission produces very radioactive / long lasting waste • fission makes lighter new elements AND fusion makes heavier new elements • fission at normal p / T AND fusion at high p / T • fusion produces more energy (than fission) B1 11(b)(i) longer half-life – radioactive substance active in body for a long time B1 shorter half-life – might be insufficient time for investigation OR it takes time / hours for the tracer to spread round the body B1 11(b)(ii) proton numbers balance for equation expected answer : 42Mo → 43Tc + –1β B1 all nucleon numbers correct B1 correct proton and nucleon number for β-particle B1 11(b)(iii) any suitable use, e.g. sterilisation of equipment, treatment of cancer, gamma for diagnosis, radiotherapy NOT any link to X-rays B1

This question in 0625/42 Oct/Nov 2020

11 (a) Fig. 11.1 shows a beam of α-particles, β-particles and γ-rays directed between two metal plates P and Q. P + + + + + + + + beam of α-particles, β-particles and γ-rays Q – – – – – – – – Fig. 11.1 The metal plates are parallel and there is a large potential difference (p.d.) between them. Plate P is positive and plate Q is negative. On Fig. 11.1, draw the paths of each of the radiations between the plates and after leaving the plates. Label the paths α, β and γ. [5] (b) State and explain one practical application of γ-rays. application … explanation … … [2] [Total: 7]

7 marks

Mark scheme: 11(a) α deflected in smooth curve away from plate P / towards plate Q B1 α continues in straight line beyond plates OR multiple paths for β and no more than a single α path B1 β deflected in smooth curve towards plate P / away from plate Q B1 β deflected more than α B1 γ passes straight through without deviation and continues in straight line beyond plates B1 11(b) suitable application e.g. sterilisation of equipment, medical diagnosis / treatment, thickness control, detecting leaks / cracks, food preservation B1 explanation e.g. destroys bacteria, destroys cancer cells, lower amount of radiation detected if thickness too large, radiation detected at site of leak, destroys microbes in food B1

This question in 0625/43 Oct/Nov 2020

10 (a) State the proton number, nucleon number and the value of the charge on an α-particle. proton number … nucleon number … charge … [3] (b) A nucleus of strontium-90 consists of 38 protons and 52 neutrons. Strontium-90 is radioactive and decays by β-emission to an isotope of yttrium. The symbol for strontium is Sr and the symbol for yttrium is Y. Write down the nuclide equation of this decay. [3] (c) The half-life of radon-220 is 56 s. A sample of radon-220 is in a container. After 112 s the mass of radon-220 is 9.2 mg. Calculate the mass of the original sample. mass = … [2] [Total: 8]

8 marks

Mark scheme: 10(a) 2 B1 4 B1 +2 B1 10(b) 90 38 Sr → 90 39 Y + − 0 1β nucleon numbers 90 on both sides of equation B1 Sr and proton number 38 on left AND Y and proton number 39 on right B1 − 0 1 β (to right of arrow) B1 10(c) (original mass = 4 / 9.2 =) 37 mg A2 2 half-lives C1

This question in 0625/42 Feb/March 2021

8 (a) Two identical radioactive sources emit α-particles and γ-rays into two vacuum tubes. (i) Fig. 8.1 shows two electrically charged plates on either side of one of the vacuum tubes. plate at +2500 V vacuum source initial path of beam of α-particles and γ-rays plate at –2500 V Fig. 8.1 Write the symbol α once in Table 8.1 to indicate any deflection of the α-particles. Write the symbol γ once in Table 8.1 to indicate any deflection of the γ-rays. Table 8.1 towards bottom of towards top of into page out of page no deflection page page [2] (ii) Fig. 8.2 shows the poles of a very strong magnet on either side of the other vacuum tube. N pole of strong magnet vacuum source N initial path of beam of α-particles S and γ-rays S pole of strong magnet Fig. 8.2 Write the symbol α once in Table 8.2 to indicate any deflection of the α-particles. Write the symbol γ once in Table 8.2 to indicate any deflection of the γ-rays. Table 8.2 towards bottom of towards top ofinto page out of page no deflection page page [2] (b) Fig. 8.3 shows a simple direct current (d.c.) electric motor with a split-ring commutator. split-ring brush coil N S X Fig. 8.3 (i) State and explain the direction of rotation of the coil as seen from point X. statement … explanation … … [3] (ii) The coil rotates through 90° from the position shown. State what happens to the moment in this position. … [1] (iii) The coil is rotated through 180° from the position shown. By considering the forces on the coil, explain how the split-ring commutator enables the motor to turn continuously. … … [2] [Total: 10]

10 marks

Mark scheme: 8(a)(i) α in Box 4 / towards bottom of page B1 γ in Box 3 / no deflection B1 8(a)(ii) α in Box 1 / into page B1 γ in Box 3 / no deflection B1 Question Answer Marks 8(b)(i) clockwise accept rotation arrow on diagram B1 force on L wire up / up arrow on L wire labelled force on diagram B1 force on RH wire down / down arrow on R wire labelled force on diagram B1 8(b)(ii) none / zero (moment) B1 8(b)(iii) current in coil reverses OR changes direction B1 force(s) (on wires in new positions) still up on L OR down on R owtte B1

This question in 0625/42 May/June 2021

11 (a) A student investigates a radioactive substance in a laboratory. Fig. 11.1 is a graph showing the count rate detected as the substance decays for 7.5 minutes. 250 count rate counts / min 200 150 100 50 0 0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 time / min Fig. 11.1 The background radiation is 20 counts / min. (i) Determine the half-life of the substance. half-life = … [3] (ii) Calculate the count rate detected at time = 9.6 minutes. count rate = … counts / min [2] (b) The substance emits α-particles and γ-rays. The student suggests that it is safe to store the substance in a plastic container of thickness 2 mm. State and explain whether the student’s suggestion is correct. statement … explanation … … [3] [Total: 8]

8 marks

Mark scheme: 11(a)(i) (initial CR adjusted for background = 220 – 20 =) 200 C1 (after 1 half-life CR adjusted for background =) 100 OR (detected CR) = 120 C1 2.4 min A1 11(a)(ii) 12 or 13 C1 (12 + 20 =) 32 OR (13 + 20 =) 33 A1 11(b) incorrect B1 container / (2 mm) plastic does not absorb / stop / block / is penetrated by γ B1 good extra detail e.g. any one of: • container / (2 mm) plastic absorbs / stops α • partially correct as statement • need lead to stop γ • γ is dangerous / harmful owtte B1

This question in 0625/42 May/June 2021

10 (a) Fig. 10.1 shows a beam of radiation in a vacuum. The beam contains α-particles, β-particles and γ-rays. region of uniform magnetic field out of the page beam of radiation, containing α, β and γ-rays Fig. 10.1 The beam enters a region where there is a strong, uniform magnetic field. The direction of the magnetic field is out of the page. On Fig. 10.1, mark and label the paths through the magnetic field of: (i) α-particles (label this path α) [1] (ii) β-particles (label this path β) [2] (iii) γ-rays (label this path γ). [1] (b) Radioactive sources have many uses in medicine. State two safety precautions which hospital staff take when working with γ-ray sources. 1. … 2. … [2] (c) The radioactive isotope iodine-131 is used as a tracer in medical diagnosis. A nucleus of iodine-131 contains 53 protons and 78 neutrons. The symbol for iodine is I. (i) Use nuclide notation to show this isotope of iodine. [1] (ii) Iodine-131 emits γ-radiation. It has a half-life of 8 hours. Explain why this emission and this half-life make iodine-131 a suitable material for a tracer in medical diagnosis. … … … … [2] [Total: 9]

9 marks

Mark scheme: 10(a)(i) curve bending downwards while in magnetic field (and labelled α) B1 10(a)(ii) curve bending in opposite direction from α while in magnetic field OR up the page if no curve shown for α in (a)(i) (and labelled β) B1 greater curvature for β than for α B1 10(a)(iii) line passing straight through magnetic field (and labelled γ) B1 10(b) any two from: • stand behind shielding provided / wall / as far away as possible • store in lead-lined boxes • limit exposure time / (monitoring exposure) with film badge • do not allow pregnant staff to work B2 10(c)(i) 131 53 I B1 10(c)(ii) any two from: • γ can be detected outside body • needs long enough half-life to be detected / reach part of the body required • needs short enough half-life to soon have very little activity • gamma weakly ionising or pass out of body without harm B2

This question in 0625/43 May/June 2021

9 Uranium‑235 (23592U) is a radioactive isotope of uranium that occurs naturally on Earth. (a) Describe the composition and structure of a neutral atom of uranium‑235. … … … … … [4] (b) Another isotope of uranium is uranium‑238. Describe how an atom of uranium‑238 differs from an atom of uranium‑235. … … [1] (c) In the reactor in a nuclear power station, a nucleus of uranium‑235 absorbs a slow‑moving neutron and then undergoes nuclear fission. Two neutrons, a nucleus of xenon‑140 (14054Xe) and a nucleus of an element represented by E are produced. Complete the equation for this fission reaction. … n + 23592U 14054Xe + … E + 2n [2] (d) Xenon‑140 (14054Xe) is radioactive. It decays by β‑emission to isotope Q. Determine: (i) the proton number of Q … [1] (ii) the nucleon number of Q. … [1] [Total: 9]

9 marks

Mark scheme: 9(a) (very small) nucleus and surrounded by electrons (in orbit / shells) B1 92 protons or 92 electrons or number of protons = number of electrons B1 protons and neutrons in nucleus B1 143 neutrons B1 9(b) (uranium-238 has) three more neutrons (in nucleus) B1 9(c) 94 (38)(E) B1 (94) 38(E) B1 9(d)(i) 55 B1 9(d)(ii) 140 B1

This question in 0625/41 Oct/Nov 2021

11 (a) Describe the composition and structure of a neutral atom of beryllium-8, which has a proton number of 4 and a nucleon number of 8. … … … … [4] (b) A radioactive isotope decays by β-emission to form an isotope of barium with nucleon number 135. Table 11.1 element symbol proton number iodine I 53 xenon Xe 54 caesium Cs 55 barium Ba 56 lanthanum La 57 cerium Ce 58 praseodymium Pr 59 Use data from Table 11.1 to write down the nuclide equation for this decay. [4] [Total: 8]

8 marks

Mark scheme: 11(a) (very small) nucleus AND (surrounded by) electrons (in orbit / shells) B1 neutrons and protons in nucleus B1 4 electrons (in atom) OR number of electrons = number of protons B1 4 neutrons (in nucleus) B1 11(b) 135 55 on left B1 Cs on left B1 135Ba 56 on right B1 +β on right OR –β on left B1

This question in 0625/42 Oct/Nov 2021

11 (a) A detector of radioactivity is placed in a laboratory where there are no radioactive samples. A student notices that the detector shows a count rate that varies between 20 counts / min and 24 counts / min. (i) Suggest a source of these readings. … [1] (ii) Explain why these readings are not constant. … [1] (b) A nucleus of uranium (U) contains 92 protons and 146 neutrons. It decays by emitting an α-particle to become a nucleus of thorium (Th). Complete the nuclide equation for this radioactive decay. … … … … U … Th + … α [3] (c) An isotope of radon has a half-life of 3.8 days. It decays by emitting α-radiation. Calculate the time taken for 16 mg of this isotope to decay to 2 mg of this isotope. time = … days [2] [Total: 7]

7 marks

Mark scheme: 11(a)(i) earth, rocks, radon gas, student etc. B1 11(a)(ii) (radioactive decay is a) random (process) B1 11(b) B3 U: proton no 92 and nucleon number 238 B1 Th: proton number 90 and nucleon number 234 B1 α: proton number 2 and nucleon number 4 B1 11(c) 11 A2 three half lives or evidence of multiplying half-life by 3 C1

This question in 0625/43 Oct/Nov 2021

10 The isotope americium-241 is represented by 24195Am. This isotope decays by an α-emission to an isotope of neptunium (Np). (a) Complete the nuclide equation for this decay. 241 … … + α 95Am Np … … [3] (b) Fig. 10.1 shows a simple diagram of a smoke detector. The smoke detector contains a small sample of americium-241. This isotope ionises the air between the metal plates in the detector. detector circuit radioactive source metal plates air flow Fig. 10.1 (i) Describe how the americium-241 ionises air. … … … … [3] (ii) Suggest and explain two reasons why smoke detectors use an isotope that emits α-particles rather than an isotope that emits γ-radiation. 1. … … … 2. … … … [2]

8 marks

Mark scheme: 10(a) 241 95Am → 237 93Np + 4 2∝ 237Np nucleon number correct for Np B1 93Np proton number correct for Np B1 + 4 2∝ alpha notation correct B1 10(b)(i) alpha (particles emitted from americium) B1 move close to / hit molecules in the air (between the metal plates) B1 removing electrons (out of the molecules) B1 Question Answer Marks 10(b)(ii) Any two from: • alpha not penetrating / short range AND alpha (particles) stopped by smoke particles • alpha (particles) more highly ionising (than gamma) AND ionise air more easily • range of alpha particles is short / alpha is not penetrating AND alpha less harmful (to humans) B2

This question in 0625/42 Feb/March 2022

10 A student places a sample of an isotope of protactinium (Pa-234) near a radiation detector. The readings on the detector, taken every 20 s, are recorded in Table 10.1. Table 10.1 count rate time / s counts / min 0 101 20 88 40 76 60 66 80 58 100 51 120 46 140 42 160 38 180 35 Fig. 10.1 shows a graph of the count rate due to this sample against time. 80 count rate counts / min 70 60 50 40 30 20 10 0 0 20 40 60 80 100 120 140 160 180 time / s Fig. 10.1 (a) Explain why the readings in Table 10.1 are not the same as those plotted on the graph. … … [2] (b) Using the graph in Fig. 10.1, determine the half-life of this isotope of protactinium. half-life = … s [2] 234(c) The nuclide notation for this isotope of protactinium is 91Pa. Protactinium-234 decays to an isotope of uranium (U) by β-emission. Write down the nuclide equation for this decay of protactinium-234. [3] [Total: 7]

7 marks

Mark scheme: 10(a) background radiation (present in values in Table 10.1) B1 (background radiation) is removed (before plotting) OR (background radiation) not present in the graph values B1 10(b) 70 ⩽ half-life ⩽ 76 (s) A2 evidence of at least one pair of values for count rate halving taken from graph C1 10(c) 234 91 Pa → 234 92 U + 0 1  92U on RHS B1 234U B1 + 0 1  on RHS B1

This question in 0625/43 May/June 2022

9 Only one isotope of gold occurs naturally on Earth. (a) State what this indicates about the nuclear structure of all the naturally occurring atoms of gold on Earth. … … [1] (b) There are several artificially produced isotopes of gold. Gold-198 (19879 Au) is an artificial isotope which is used in medicine and in scientific research. Gold-198 decays by β (beta)-emission to a stable isotope of mercury. (i) Determine the number of protons and the number of neutrons in a nucleus of this isotope of mercury. number of protons = … number of neutrons = … [2] (ii) A sample of gold-198 is placed near to a radiation detector in a research laboratory. The count rate is recorded at the same time every day for 32 days. The results are used to plot the graph shown in Fig. 9.1. 400 count rate counts / min 300 200 100 0 0 4 8 12 16 20 24 28 32 time / days Fig. 9.1 Using Fig. 9.1, determine the background count rate in the research laboratory. count rate = … [1] (iii) Using Fig. 9.1, determine the half-life of gold-198. half-life = … [4] [Total: 8]

8 marks

Mark scheme: 9(a) they all have the same number of neutrons / nucleons or they are all identical B1 9(b)(i) B2 (number of protons =) 80 B1 (number of neutrons =) 118 B1 9(b)(ii) 19 counts / minute ⩽ count rate ⩽ 21counts / minute B1 9(b)(iii) 2.4 days ⩽ ⩽ 2.9 days A4 count rate from line – background count e.g. 390 – 20 C1 answer from first C1 mark divided by 2 e.g. 370 / 2 or 185 C1 background count + answer from second C1 mark e.g. 20 + 370 / 2 or 20 + 185 or 205 C1

This question in 0625/41 Oct/Nov 2022

10 (a) The magnitude of the charge on a β (beta)-particle is 1.6 × 10–19 C. (i) State the proton number and nucleon number of an α (alpha)-particle. proton number … nucleon number … [2] (ii) Determine the magnitude of the charge of an α (alpha)-particle. charge … [1] (b) A nucleus of radium-230 consists of 88 protons and 142 neutrons. Radium-230 is radioactive and decays by β (beta)-emission to an isotope of actinium. The symbol for radium is Ra and the symbol for actinium is Ac. Write down the nuclide equation for this decay. [3] (c) The half-life of radium-230 is 93 min. A sample contains 9.6 × 10–12 g of radium-230. Calculate the mass of radium in the sample after 279 min. mass = … [2] [Total: 8]

8 marks

Mark scheme: 10(a)(i) (proton number) 2 B1 (nucleon number) 4 B1 10(a)(ii) 3.2  10–19 (C) B1 10(b) 230 88 Ra → 23089 Ac + –10  A3 any two from: C2 • nucleon numbers 230 on left AND 230 on right • Ra and proton number 88 on left AND Ac and proton number 89 on right • 0  . –1 10(c) (mass =) 1.2  10–12 g A2 3 half-lives OR 9.6  10–12 / 8 OR 9.6  10–12 / 23 C1

This question in 0625/42 Oct/Nov 2022

10 (a) A cloud chamber can be used to detect α (alpha)-particles and β (beta)-particles. Alcohol in the cloud chamber exists as a vapour and condenses on ions produced in the air. This forms visible tracks. Fig. 10.1 shows the tracks when a source of α-particles and β-particles is present in the cloud chamber. cloud chamber alcohol vapour in air source of α-particles and β-particles Fig. 10.1 Some of the tracks are short and thick. Other tracks are longer and thinner. State and explain which tracks are produced by α-particles and which tracks are produced by β-particles. α-particles … … β-particles … … [3] (b) A radioactive isotope of sodium (Na) is used to detect leaks from water pipes. A nucleus of this isotope of sodium contains 11 protons and 13 neutrons. This nucleus decays by emitting a β-particle to form a nucleus of magnesium (Mg). (i) Describe what is meant by an isotope. … … … [2] (ii) Write down the nuclide equation for the decay of this isotope of sodium to magnesium. [3] (iii) This isotope of sodium has a half-life of 15 hours. The isotope of magnesium is stable and does not undergo radioactive decay. Suggest why these properties of the isotope of sodium and the isotope of magnesium make this isotope of sodium suitable to detect leaks from water pipes. … … … [2] [Total: 10]

10 marks

Mark scheme: 10(a) -particles are short and thick / -particles are long and thin B1 any two from: B2 • -particles are more ionising / -particles are less ionising • -particles are less penetrating or have shorter range / -particles are more penetrating or have longer range • -particles have more energy / -particles have less energy 10(b)(i) (element with) same number of protons B1 (element with) different number of neutrons B1 10(b)(ii) 24 24 0 Na → Mg + 11 12 −1 Na on left with correct proton and nucleon number B1  on right with correct proton and nucleon number B1 Mg on right with correct proton and nucleon number B1 10(b)(iii) half life (of Na 24) long enough (to allow detection of leaks) B1 negligible amount (of Na 24) remains in liquid after a few days B1 (so) less hazardous (to human health) OR decays to something stable/magnesium (is stable) AND (so) less hazardous (to human health)

This question in 0625/43 Oct/Nov 2022

9 (a) A nuclear power station has a reactor where controlled nuclear fission of uranium‑235 takes place. (i) Explain what is meant by nuclear fission. … … … … … [3] (ii) State one advantage and one disadvantage of generating electrical power in nuclear power stations compared with electrical power generated using wind turbines. advantage … disadvantage … [2] (b) Deuterium is an isotope of hydrogen (H) with 1 proton and 1 neutron. Nuclear fusion occurs when two nuclei of deuterium combine. An isotope of helium (He) and a neutron are formed. Use nuclide notation to write down the nuclide equation for this reaction. [3] [Total: 8]

8 marks

Mark scheme: 9(a)(i) large unstable nucleus OR neutrons hit nucleus OR neutrons are released (from nucleus) B1 (large) nucleus splits (into smaller nuclei) B1 (large) release of energy B1 9(a)(ii) advantage – one from: B1 • Continuous supply of energy • not affected by the weather OR not affected by wind strength • produces large amounts of energy disadvantage – one from: B1 • resources finite / not renewable • cost / difficulty of building / cost / difficulty of decommissioning • danger if any leak of radiation • produces hazardous / dangerous waste OR difficulty of storage of used radioactive material OR nuclear waste must be stored for a long time 9(b) 21H + 21H → 32He + 0n1 LHS correct B1 32He on RHS B1 0n1 on RHS B1

This question in 0625/42 Feb/March 2023

9 Fig. 9.1 represents all the particles in a neutral atom of a radioactive isotope X1. Fig. 9.1 (not to scale) (a) Determine the number of neutrons in this atom and explain how the answer is obtained. number of neutrons = … explanation … … [2] (b) The isotope X1 is a beta emitter that decays to the stable isotope X2. (i) Describe how a nucleus of X2 differs from a nucleus of X1. … … [2] (ii) Suggest why isotope X2 is stable whereas X1 is not stable. … … [1] (c) The half-life of X1 is approximately 20 ms. (i) Define the term half-life. … … … [2] (ii) Suggest one reason why isotopes with very short half-lives are especially hazardous. … … [1] [Total: 8]

8 marks

Mark scheme: 9(a) (number of neutrons =) 7 B1 any one from:  number of electrons = number of protons  white dots are protons / there are 5 protons  grey dots are neutrons  (number of neutrons) = 12 – 5 B1 9(b)(i) (X2 has) one more proton more and one fewer neutron (than X1) OR (X2 has) 6 protons and 6 neutrons A2 (X2 has) one neutron fewer / one more proton (than X1) OR (X2 has) 6 protons / 6 neutrons C1 9(b)(ii) (X2) has fewer (excess) neutrons (in its nucleus) ORA B1 9(c)(i) time (taken) M1 for number of (radioactive) nuclei / atoms (in a sample of X1) to halve OR for rate of decay to halve A1 9(c)(ii) large number of particles produced in short time OR high / large decay rate OR high dose (of radiation) in short time B1

This question in 0625/41 May/June 2023

9 (a) Table 9.1 shows some properties and values for α-particles, β-particles and γ-radiation. Complete Table 9.1. Table 9.1 type of number of number of charge / C stopped by radiation protons neutrons α 2 + 3.2 × 10–19 thin sheet of paper β 0 thin sheet of aluminium γ 0 [3] (b) State how β-decay changes the nucleus of an atom. … [1] (c) A radiation detector used in a laboratory detects a background count rate of 30 counts / min. A radioactive source is placed in front of the radiation detector. The initial reading on the detector is 550 counts / min. The half-life of the source is 25 minutes. Calculate the expected reading on the detector after 75 minutes. reading = … counts / min [4] (d) State two safety precautions taken when moving, using or storing radioactive sources in a laboratory. 1 … 2 … [2] [Total: 10]

10 marks

Mark scheme: 9(a) B1  – no. of protons 0 and charge –1.6  10–19 B1  – no. of neutrons 0 and charge 0 and (very) thick concrete / thick lead B1 9(b) (the nucleus has) one less neutron and one more proton B1 9(c) 95 (counts / min) A4 initial count rate due to source = 550 – 30 (counts / min) OR 520 seen C1 (75 min =) 3 half-lives OR (count rate =) 1 / 8 (of initial count rate) C1 final count rate due to source = (520 / 8 =) 65 C1 9(d) any two from:  limit time of exposure  store sources in lead boxes  keep distance from sources  avoid contact OR use tongs OR wear gloves B2

This question in 0625/42 May/June 2023

8 (a) During β-decay, one of the neutrons in the nucleus changes. (i) State what happens to this neutron. … [1] (ii) Explain how charge is conserved during this change. … … … [2] (b) Complete the nuclide equation for the α-decay of radon-212 to form an isotope of polonium, symbol Po. 21286Rn [3] [Total: 6]

6 marks

Mark scheme: 8(a)(i) B1 8(a)(ii) charge on neutron = 0 OR total charge on products = 0 B1 charge on proton = +1 AND charge on electron = –1 B1 8(b) ( 212 86Rn ) 208 84Po +  4 2 A3 any two from:  proton numbers balance  nucleon numbers balance   4 2 OR H 2 4 e seen C2

This question in 0625/43 May/June 2023

8 The isotope uranium-235 is represented by 235 92 U. (a) State what the numbers 92 and 235 represent in this symbol. 92 is … 235 is … [2] (b) Uranium-235 is a fuel used in nuclear reactors. (i) State the process by which energy is released from uranium-235 in a nuclear reactor. … [1] (ii) A nuclide equation for this process is 235 92 U + 10 n 14054 Xe + 9438 Sr + 2 10 n. Describe the mass and energy changes that take place during this process in a nuclear reactor. … … … [2] (c) (i) Describe how thermal energy from nuclear reactions is used to generate electricity in a power station. … … … … [3] (ii) State one advantage and one disadvantage of using nuclear fuels in a power station instead of using fossil fuels. advantage … … disadvantage … … [2] [Total: 10]

10 marks

Mark scheme: 8(a) (92 is) the proton number / number of protons (in the nucleus) / atomic number B1 (235 is) the nucleon number / number of nucleons (in the nucleus) / mass number B1 8(b)(i) (nuclear) fission B1 8(b)(ii) nucleus converted to (more stable) nuclei with smaller total mass B1 mass (difference) is released / converted as (kinetic) energy (of products) / thermal energy B1 8(c)(i) any three from: B3 • (thermal energy) used to heat / boil (cold) water OR make steam • steam is at high pressure • steam drives a turbine • turbine (connected to and) drives a generator • turbine moves a coil in a magnetic field 8(c)(ii) advantage - any one from: B1 • (much) small(er) amount of fuel needed (to produce same amount of energy) • no greenhouse gases produced OR low carbon dioxide emissions • no air pollution (when operating normally) disadvantage – any one from B1 • danger if any leak of radiation • produces hazardous / dangerous / toxic waste OR difficulty of storage of used radioactive material OR nuclear waste must be stored for a long time • expensive to build or decommission nuclear power plant or store nuclear waste

This question in 0625/42 Oct/Nov 2023

9 (a) For each application of radioactive isotopes, state and explain which type of radioactive emission is suitable and suggest an appropriate half-life for the isotope. (i) household smoke alarm type of radioactive emission … explanation … … half-life … [3] (ii) measuring the thickness of aluminium strips produced in a factory type of radioactive emission … explanation … … half-life … [3] (b) Lead-208 (20882Pb) has the highest nucleon number of the stable isotopes of lead. Explain why lead-214 (21482Pb) is radioactive. … … … … [2] (c) State two different sources of background radiation. 1 … 2 … [2] [Total: 10]

10 marks

Mark scheme: 9(a)(i) alpha B1 highly ionising B1 OR not (very) penetrating any value between 10–500 years B1 9(a)(ii) beta B1 absorption depends on thickness (of aluminium) B1 any number of years B1 9(b) too many neutrons B1 decay reduces number of neutrons B1 9(c) any two from: B2 • radon gas (in the air) • rocks OR buildings • food OR drink • cosmic rays Question Answer Marks

This question in 0625/43 Oct/Nov 2023

9 (a) An experiment directs alpha particles at a very thin sheet of gold foil. (i) Most of the alpha particles pass through the thin foil in a straight line. State the conclusion about atoms from this observation. … … [1] (ii) Some of the alpha particles are deflected through angles less than 90° and a few are deflected through 180°. State and explain two conclusions about the nuclei of atoms from this observation. conclusion 1 … explanation 1 … … conclusion 2 … explanation 2 … … [4] (b) A source contains a radioactive isotope of strontium. This isotope decays by emission of β‑particles. The half‑life of this isotope is 29 years. (i) State the change in the nucleus which occurs when a β‑particle is emitted. … [1] (ii) The initial mass of this isotope of strontium in the source is 25 µg. Calculate the mass of the strontium isotope that decays in 87 years. mass = … µg [3] [Total: 9]

9 marks

Mark scheme: 9(a)(i) most of the atom is empty space B1 9(a)(ii) any two from: B2 1 the nucleus is very small 2 mass of gold nucleus is much greater than mass of alpha particle 3 the nucleus is positively charged corresponding explanation to conclusion: B2 1 not many alpha particles pass close to the nucleus / owtte 2 large force between alpha and nucleus (has bigger effect on small mass of alpha) 3 alpha particles are positively charged, AND force is repulsive 9(b)(i) (in the nucleus a) neutron is changed into a proton (and an electron which is the emitted -particle) B1 9(b)(ii) 22 g A3 (87 years is) three half-lives OR 25 / 8 OR 87 / 29 = 3 (half lives) (C1) 1 / 8th (of the strontium remains) OR 25 / 8 (decays) OR 3.125 seen (C1)

This question in 0625/42 Feb/March 2024

8 The isotope thallium-208 (20881Tl ) is radioactive. It decays by β-decay. (a) Thallium-208 decays to an isotope of lead (Pb). (i) Complete the equation for this decay. … … 20881Tl … Pb + … β [3] (ii) The β-emission of thallium-208 is accompanied by γ-emission from the nucleus. Explain why this γ-emission does not affect the numbers in the equation in (a)(i). … … [1] (iii) Suggest one reason why a nucleus of thallium-208 is unstable. … … [1] (b) A sample of thallium-208 is placed in a thick lead container. Fig. 8.1 shows a narrow beam of β-particles and γ-radiation emerging from a small hole in one side of the container. magnetic field into page beam of β-particles and γ-radiation sample of thallium-208 Fig. 8.1 The narrow beam enters a region where there is a magnetic field that is directed into the page. On Fig. 8.1: • draw a line labelled β to indicate the path of the β-particles in the magnetic field • draw a line labelled γ to indicate the path of the γ-radiation in the magnetic field. [3] [Total: 8]

8 marks

Mark scheme: 8(a)(i)  –1 Pb ….. 208 B1 Pb 82 ….. B1 8(a)(ii) -emission / it consists of waves / rays OR -emission has no mass / charge B1 8(a)(iii) (it contains) too many / excess of neutrons OR (nucleus is) too heavy B1 8(b) smooth curve (through magnetic field) AND labelled  B1 path towards bottom of page AND no upward component AND labelled  B1 (continuation of beam along) horizontal line through magnetic field AND labelled  B1

This question in 0625/41 May/June 2024

9 (a) Radioactive isotopes that emit ionising radiation are used in hospitals. (i) State and explain two safety precautions necessary for the use of these isotopes in medical procedures. safety procedure 1 … explanation … … safety procedure 2 … explanation … … [2] (ii) Give two reasons why alpha‑emitters are not used as radioactive tracers inside the body. 1 … … 2 … … [2] (b) Sodium‑24 is an isotope of sodium (Na) that has a proton number of 11 and a nucleon number of 24. Sodium‑24 decays by emission of a beta‑particle to form an isotope of magnesium (Mg). Use nuclide notation to write down the nuclide equation for this decay. [3] [Total: 7]

7 marks

Mark scheme: 9(a)(i) any two from:  reduce exposure time AND low(er) amount of radiation absorbed  increase distance between source and hospital staff AND lower amount of radiation reaches staff  use of shielding (e.g. walls, lead etc.) AND radiation absorbed by shielding / cannot penetrate through shielding  use isotopes with short half-life AND lower amount of radiation emitted from patient / radiation (above background) emitted for a shorter period of time  use of film badge / dosimeter AND manage individuals exposure owtte  restrict pregnant staff / patient in hospital AND radiation may harm foetus owtte B2 9(a)(ii) high ionisation (within body) B1 radiation would not reach detector (outside body) B1 9(b) Na 11 24 → Mg 12 24 +  -1 0 Na 11 24 on LHS B1  -1 0 on RHS B1 Mg 12 24 on RHS B1

This question in 0625/42 May/June 2024

10 Leaks in underground water pipes are detected using radioactive tracers. Fig. 10.1 shows a radiation detector above a water pipe. 382 counter detector pipe ground leak Fig. 10.1 (a) Before the radioactive tracer is added to the water, the detector measures the background radiation above the pipe. The average background radiation is 26 counts / minute. (i) Define background radiation. … … [1] (ii) Suggest one source of radiation that may make a significant contribution to the background count rate. … [1] (iii) A radioactive tracer is added to the water. The counter in Fig. 10.1 shows the count rate in counts / minute above the leak in the water pipe. Determine the count rate due to the tracer. count rate = … [2] (b) Suggest which radioactive emission, alpha, beta or gamma, is suitable for detecting the leak in the water pipe. Explain your answer. emission … explanation … … [3] (c) (i) Explain why the radioactive isotope must not have a very short half-life. … … [1] (ii) Explain why the radioactive isotope must not have a very long half-life. … … [1] [Total: 9]

9 marks

Mark scheme: 10(a)(i) radiation (always) present in the environment OR radiation from natural sources B1 10(a)(ii) radon gas OR rocks / buildings OR cosmic rays OR food / drink B1 10(a)(iii) 356 counts / min A2 (corrected count rate =) count rate – background count OR 382–26 C1 10(b) beta OR gamma B1 alpha would be stopped by soil and not reach detector OR beta has sufficient range to be detected above ground OR alpha and beta stopped by soil before reaching detector B1 gamma would pass through intact pipe as well cracked pipe so no difference detected OR beta stopped by intact pipe so variation between piped water and escaped water can be detected OR gamma is only radiation that will reach detector through soil OR less gamma reaches detector through solid pipe B1 10(c)(i) (very short half-life) doesn’t allow time for detection before activity has dropped to too low a level OR doesn’t allow for sufficient build up at the leak to detect difference in rate 10(c)(ii) (very long half-life) contaminates water supply

This question in 0625/43 May/June 2024

8 The nuclide notation for the radioactive isotope carbon-14 is 146C. (a) Using the symbols shown in Fig. 8.1, draw a diagram to show the number of electrons, neutrons and protons in a neutral atom of carbon-14 and how they are arranged. symbols: electron neutron proton Fig. 8.1 [3] (b) Describe how the composition of a neutral atom of carbon-14 is different from the composition of a neutral atom of nitrogen-14 (147N). … … [2] (c) Carbon-14 decays by beta (β) emission. (i) State the name of a particle that is identical to a beta-particle. … [1] (ii) Describe the change that takes place in carbon-14 as a beta-particle is emitted. … … [1] (d) The half-life of carbon-14 is 5700 years. A very old object is made of wood. It contains 1.2 × 1011 atoms of carbon-14. When it was manufactured, it contained 9.6 × 1011 atoms of carbon-14. Determine the time that has passed since it was manufactured. time passed = … [3] [Total: 10]

10 marks

Mark scheme: 8(a) 6 electrons AND 6 protons (i.e. 6  AND 6 ) B1 8 neutrons (i.e. 8 ) B1 protons and neutrons in nucleus AND electrons orbiting nucleus B1 8(b) (carbon) has one more neutron OR nitrogen has one fewer neutron B1 (carbon) has one fewer proton / electron OR nitrogen has one more proton / electron B1 8(c)(i) electron B1 8(c)(ii) a neutron changes into a proton (and electron) B1 8(d) 17 000 years A3 1.2  1011 / 9.6  1011 OR 1 / 8 OR one halving seen e.g. 9.6  1011  2 C1 3 (half-lives) OR 1 / 8  9.6  1011 = 1.2  1011 C1

This question in 0625/41 Oct/Nov 2024

8 An isotope of boron is used in the treatment of cancer in the brain. Boron sticks to cancer cells in the brain. (a) The isotope of boron is bombarded with neutrons then undergoes fission to form lithium and alpha‑particles. (i) Describe one difference between fission and fusion. … … [1] (ii) A nucleus of boron (B) contains 5 protons and 5 neutrons. Complete the nuclide equation for this fission reaction. … B + 10n … Li + … α … [3] (b) The alpha‑particles destroy the cancer cells. Suggest and explain one reason why alpha particles are more suitable than gamma radiation for use in this treatment of brain cancer. … … … [2] (c) Other cancers are treated with gamma radiation. Describe one safety precaution a nurse or radiologist takes during this treatment. … … [1] [Total: 7]

7 marks

Mark scheme: 8(a)(i) fission is splitting of nuclei OR fusion is the joining of nuclei B1 8(a)(ii) 10 5𝐵+ 10𝑛 → 73𝐿𝑖 + 42𝛼 B: proton number 5 and nucleon number 10 B1 Li: proton number 3 and nucleon number 7 B1 : proton number 2 and nucleon number 4 B1 8(b) alpha is less penetrating / has shorter range (than gamma) B1 alpha more easily absorbed / stopped by cancer / tumour cells or won’t travel beyond cancer cells or so won’t damage B1 other / healthy cells OR alpha highly ionising (than gamma) (B1) will destroy / damage cancer cells more easily (B1) 8(c) any one from: B1 • reduce exposure time • increase distance between source and living tissue or stand in another room whilst radiation is emitted • use shielding or wear a lead apron or stand behind a glass partition / lead barrier

This question in 0625/43 Oct/Nov 2024

9 Strontium-90 is a radioactive isotope of strontium. The nuclide notation for strontium-90 is: 9 0 3 8Sr (a) (i) Explain what isotopes are. … … [1] (ii) Complete Table 9.1 for strontium-90. Table 9.1 particle number in one atom location 38 outside nucleus neutron 38 inside nucleus [2] (b) Strontium-90 is used to measure the thickness of metal sheets in industry. Strontium-90 decays by emitting beta (β) particles which pass through a metal sheet to a detector. (i) One metal sheet is 0.75 mm thick. Suggest why strontium-90 is a suitable radioactive source to measure the thickness of the metal sheets. … … … [2] (ii) The half-life of strontium-90 is approximately 27 years. Fig. 9.1 shows the shape of a decay curve. 100 percentage of 75 strontium-90 remaining 500 25 0 0 5 10 15 20 25 30 35 40 45 50 55 60 age of sample / years Fig. 9.1 The strontium-90 source is replaced with a new source after 15 years. Using Fig. 9.1, suggest why a strontium-90 source that is more than 15 years old needs to be replaced with a new source. … … [2] [Total: 7]

7 marks

Mark scheme: 9(a)(i) (isotopes are) forms of an element with the same number of protons but a different number of neutrons (in the nucleus) OR B1 (isotopes are) the same element with a different number of neutrons 9(a)(ii) B1 particle number in each location atom of strontium electron 38 outside nucleus neutron proton 38 Inside nucleus B1 particle number in each location atom of strontium 38 outside nucleus neutron 52 Inside nucleus 38 Inside nucleus 9(b)(i) (there is a) different count rate with different thicknesses of metal OR number of -particles detected varies with thickness A2 (beta () particles) can penetrate thin / 0.75mm metal OR (beta () particles) are stopped by thick metal C1 9(b)(ii) (approximate) percentage of source remaining (after 15 years) stated AND in range 63–70% B1 (approximate) percentage of sample lost (after 15 years) stated AND in range 30–37% Any one from: B1 • count rate / activity (too) low (to detect differences in thickness) owtte • detector needs high activity (to detect differences in thickness) owtte • count rate / activity too close to background owtte • less difference in activity for different thicknesses owtte

This question in 0625/42 Feb/March 2025

9 Strontium-90 (9038Sr) is a radioactive isotope that contains 38 protons and 52 neutrons. Strontium-90 decays to form an isotope of yttrium (Y) by emitting beta (β) particles. (a) (i) Suggest how the nucleus of a stable isotope of strontium differs from a nucleus of strontium-90. Explain your answer. suggestion … explanation … … [2] (ii) Complete the nuclide equation for the decay of strontium-90 to yttrium. … … 90 38Sr … Y + … β [2] (iii) Explain why scientists limit the amount of time they are exposed to radioactive strontium. … … [2] (b) Yttrium is also unstable. A scientist places a sample of yttrium near a radiation detector. Table 9.1 shows the count rate recorded by the detector as the sample decays. Table 9.1 recorded count rate time / h counts / min 0 68 50 49 100 38 150 32 200 26 250 24 300 20 350 21 400 20 Fig. 9.1 shows a graph of the count rate due to yttrium against time. 48 44 count rate 40 due to yttrium counts / min 36 32 28 24 20 16 12 8 4 0 0 20 40 60 80 100 120 140 160 180 200 220 240 260 280 300 320 time / h Fig. 9.1 (i) Use Fig. 9.1 to determine the half-life of yttrium. Show your working. half-life = … h [3] (ii) Explain the difference between the count rate in Table 9.1 and the count rate due to yttrium plotted on the graph in Fig. 9.1. … … … [1] [Total: 10]

10 marks

Mark scheme: 9(a)(i) (stable isotope) has fewer neutrons AND radioactive isotopes (usually) have an excess of neutrons A2 OR (stable isotope) has fewer neutrons AND radioactive isotopes are too heavy any one from: C1 • (stable isotope) has fewer neutrons • radioactive isotopes (usually) have more neutrons • radioactive isotopes are too heavy 9(a)(ii) 90 B1 39Y –10 B1 9(a)(iii) ionising radiation is harmful (to humans) OR A2 beta particles are ionising and harmful (to humans) any one from: C1 • radiation is / beta particles are harmful • beta particles ionise • it ionises AND is harmful 9(b)(i) 72 ⩽ half-life ⩽ 76 (h) A3 braille: 80 h (mark based on candidate choice of halving) evidence of count rate halved e.g. 48  2 = 24 C1 evidence on graph or in working that Fig. 9.1 is used to find time for count rate to halve C1 9(b)(ii) any one from: B1 • table includes background radiation owtte • graph does not have background count rate owtte • graph has corrected count rate

This question in 0625/41 May/June 2025

9 (a) (i) State what is meant by background radiation. … … [1] (ii) State one source that makes a significant contribution to background radiation. … [1] (b) Radioactive isotopes are used in some medical treatments. Radium-223 (22388Ra) is an isotope of radium. Radium-223 decays by the emission of alpha (α) particles to an isotope of radon (Rn). (i) Complete the nuclide equation for this decay. … … 223 88Ra … Rn + … α [2] (ii) Radium-223 is injected into the body to treat a specific organ. Explain why the source must be inside the body. … … [1] (c) An isotope of technetium is injected into the body to detect cancer in one of the organs. The half-life of this isotope is 6 hours and it decays by emitting gamma (γ) radiation. The radiation is detected outside the body. (i) Explain why a source of gamma radiation is used. … … [1] (ii) Explain why a source with a short half-life must be used. … … [1] [Total: 7]

7 marks

Mark scheme: 9(a)(i) radiation (always) present in the environment OR radiation from natural sources B1 9(a)(ii) any one from: B1 • radon gas • rocks OR buildings • food OR drink • cosmic rays 9(b)(i) 219 86Rn B1 4 2  B1 9(b)(ii) alpha (particles) would be absorbed / stopped by the skin owtte B1 9(c)(i) gamma / radiation needs to pass out of the body (to detector) B1 9(c)(ii) after a few days / some time, little radiation is emitted owtte B1

This question in 0625/42 May/June 2025

11 (a) Define the half-life of a radioactive source. … … [1] (b) A protactinium (Pa) nucleus decays into a uranium (U) nucleus by the emission of a beta particle (β-particle). (i) Complete the nuclear equation for the decay. 23 4 9 1Pa [3] (ii) State the change that occurs in the nucleus during the decay. … [1] (c) A different element decays by the emission of an alpha particle (α-particle). Give two reasons why α-particles are more strongly ionising than β-particles. 1 … … 2 … … [2] [Total: 7]

7 marks

Mark scheme: 11(a) time taken for half the nuclei (in any sample) to decay B1 11(b)(i) 234(U) B1 92U B1 + 0  B1 -1 11(b)(ii) neutron changes to a proton (plus an electron) B1 11(c) ( particles have) greater kinetic energy (than  particles) B1 ( particles have) greater charge (than  particles) B1

This question in 0625/43 May/June 2025

9 (a) Fig. 9.1 shows a beam of radiation in a vacuum. The beam contains α‑particles, β‑particles and γ‑radiation. region of uniform magnetic field into the page beam of radiation containing α-particles, β-particles and γ-radiation Fig. 9.1 The beam enters a region where there is a strong, uniform magnetic field. The direction of the magnetic field is into the page. On Fig. 9.1 draw and label the paths within the magnetic field of: (i) α‑particles (label this path α) [1] (ii) β‑particles (label this path β) [2] (iii) γ‑radiation (label this path γ) [1] (b) Table 9.1 shows five radioactive sources, the main type of radiation emitted by each source and the half‑life of each source. Table 9.1 radioactive type of radiation half‑life source emitted P alpha 460 years Q alpha 10 days R beta 29 years S beta 14 days T gamma 30 years (i) Define half‑life of a radioactive isotope. … … [1] (ii) Fig. 9.2 shows a simplified diagram of a machine that produces thin sheets of aluminium of constant thickness. radioactive rollers source aluminium sheet radiation detector machinery to control roller Fig. 9.2 The radiation detector is used to measure the thickness of the aluminium sheets and control the gap between the rollers. State the most suitable radioactive source in Table 9.1 for the machine in Fig. 9.2. Explain why this radioactive source is the most suitable and why the other sources are unsuitable. most suitable source … explanation … … … … … … … [4] [Total: 9]

9 marks

Mark scheme: 9(a)(i) curve bending upwards while in magnetic field and labelled  B1 9(a)(ii) curve bending downwards while in magnetic field and labelled  B1 smaller radius of curvature for β than for α B1 9(a)(iii) line passing straight through the magnetic field and labelled  B1 9(b)(i) time taken for half the nuclei of a sample to decay B1 9(b)(ii) R B1 half-life not too short OR half-life is suitable so that source does not need to be replaced often B1 so count rate changes with thickness B1 γ- rays would not be stopped at all AND α-particles would be absorbed by any thickness of aluminium B1

This question in 0625/42 Oct/Nov 2025