radiation poisoning is insufficient ionising is insufficient 1 3 (b) (i) any one from: • use tongs to pick up source • wear gloves • use (lead) shielding • minimise time (of exposure) • maximise distance (between source and teacher). accept any other sensible and practical suggestion ignore reference to increasing / decreasing the number / thickness of lead sheets 1 (ii) background 1 Page 5 of 44
(c) (i) curve drawn from point 2,160 do not accept straight lines drawn from dot to dot 1 (ii) (also) increases less radiation passes through is insufficient 1 (iii) 50 accept any value from 40 to 56 inclusive 1 (d) gamma 1 only gamma (radiation) can pass through lead accept alpha and beta cannot pass through lead a general property of gamma radiation is insufficient 1  (a) (average) time taken for the amount / number of nuclei / atoms (of the isotope in a sample) to halve or time taken for the count rate (from a sample containing the isotope) to fall to half accept (radio)activity for count rate 1 4 (b) 60 ±3 (days) 1 indication on graph how value was obtained 1 (c) (i) cobalt(-60) 1 gamma not deflected by a magnetic field or gamma have no charge dependent on first marking point accept (only) emits gamma gamma has no mass is insufficient do not accept any reference to half-life 1 (ii) strontium(-90) 1 Page 6 of 44
any two from: • only has beta • alpha would be absorbed • gamma unaffected • beta penetration / absorption depends on thickness of paper if thorium(-232) or radium(-226) given, max 2 marks can be awarded 2 (iii) cobalt(-60) 1 shortest half-life accept half-life is 5 years dependent on first marking point 1 so activity / count rate will decrease quickest 1 (iv) americium(-241) / cobalt(-60) / radium(-226) 1 gamma emitter 1 (only gamma) can penetrate lead (of this box) do not allow lead fully absorbs gamma 1  (a) (i) nuclear reactor 1 5 star 1 (ii) nuclei are joined (not split) accept converse in reference to nuclear fission do not accept atoms are joined 1 Page 7 of 44
(b) (i) any four from: • neutron • (neutron) absorbed by U (nucleus) ignore atom do not accept reacts do not accept added to • forms a larger nucleus • (this larger nucleus is) unstable • (larger nucleus) splits into two (smaller) nuclei / into Ba and Kr • releasing three neutrons and energy accept fast-moving for energy 4 (ii) 56 (Ba) 1 57 (La) if proton number of Ba is incorrect allow 1 mark if that of La is 1 greater 1 accept e for β scores 3 marks 1  (a) (i) 18 1 6 (ii) the count rate for the source 1 (iii) the alpha radiation would not cover such a distance 1 (iv) plots correct to within ½ small square allow 1 mark for 4 correct points plotted 2 correct curve through points as judged by eye 1 (v) two attempts at finding ‘half-distance’ using the table 20 to 10 cpm d = 0.4 m 125 to 56 cpm d = 0.2 m 31 to 14 cpm d = 0.4 m allow 1 mark for one attempted comparison 2 Page 8 of 44
obeyed or not obeyed dependent on previous two marks 1 (b) (i) there is no effect on the count rate in experiment 1 because the field is parallel or beta particles are not deflected or there is no force 1
You've reached the end of your free preview.
Want to read all 44 pages?
- Fall '16
- I don't remember
- Alpha, Ionizing radiation, accept α