(c) same mass/nucleon number but a neutron changes to a proton atomic/proton number increases ignore GAINS a proton beta by 1 (1) particle /electron given off (negative) beta (1) (2) (d)(i) Alpha ray, alpha particle, (1) α Ignore capital letters (d)(ii) A description including two of the particles with higher energy one increases as other increases travel further (1) rate of increase is in the accept values quoted from graph range from 1.17 to 1.33 not (quite) linear/not (cm/MeV) (1) range gradually proportional /curves upwards increases more with energy (1) accept values quoted from graph (2) (e) reaction needs a neutron idea of continuous nature of from one fission to reach another reaction uranium nucleus/atom (at the the neutrons would be going too right speed) (1) (fission of 238) slowly /do not have enough needs energy / lose energy too fast fast/high(er) energy neutrons (1) (2) Q23. Answer Acceptable answers Mark (a) A (1) axes labelled correctly With (b) (3) activity / Bq / count rate or unit (1) correct shaped ignore radioactivity smooth curve (1) line does not time/ seconds/ any time unit reach zero activity (1) (c)(i) Idea of 2 half-lives (1) 11 400 / 5700 = 2 2.2 (Bq) for (3) 11 400 = 2 × 5700 Idea of marks halving activity twice (1) 0.55 × 2 × 2 Calculation (1) 2.2 (Bq) (c)(ii) Explanation linking two of: (2) accept interfering / t Background radiation affects  including varies with the measurement (1) place/time/random nature Needs to be subtracted from  repeating test improves reliability readings (1) Background radiation is  variable (1) Background radiation needs  to be averaged (1) (c)(iii) One relevant idea: ignore better method/results / (1) (New method) more accurate (1) more reliable difficult to grad Hard to measure a small activity distinguish between the reading (1) Background radiation affects and background readings (1) Need to find difference of two small quantities (1) Can test smaller samples (1) Total for question = 10 marks
(c) same mass/nucleon number but atomic/proton number increases by 1 (1) (negative) beta (1) a neutron changes to a proton ignore GAINS a proton beta particle /electron given off (2) (d)(i) Alpha ray, alpha particle, α Ignore capital letters (1) (d)(ii) A description including two of one increases as other increases (1) rate of increase is in the range from 1.17 to 1.33 (cm/MeV) (1) range gradually increases more with energy (1) the particles with higher energy travel further accept values quoted from graph not (quite) linear/not proportional /curves upwards accept values quoted from graph (2) (e) reaction needs a neutron from one fission to reach another uranium nucleus/atom (at the right speed) (1) (fission of 238) needs fast/high(er) energy neutrons (1) idea of continuous nature of reaction the neutrons would be going too slowly /do not have enough energy / lose energy too fast (2) Q23. Answer Acceptable answers Mark (a) A (1) (b) axes labelled correctly With or unit (1) correct shaped smooth curve (1) line does not reach zero activity (1) activity / Bq / count rate ignore radioactivity time/ seconds/ any time unit (3) (c)(i) Idea of 2 half-lives (1) 11 400 = 2 × 5700 Idea of halving activity twice (1) 0.55 × 2 × 2 Calculation (1) 2.2 (Bq) 11 400 / 5700 = 2 2.2 (Bq) for marks (3) (c)(ii) Explanation linking two of:  Background radiation affects the measurement (1)  Needs to be subtracted from readings (1)  Background radiation is variable (1)  Background radiation needs to be averaged (1) accept interfering / including varies with place/time/random nature repeating test improves reliability (2) t (c)(iii) One relevant idea: (New method) more accurate (1) Hard to measure a small activity (1) Background radiation affects readings (1) Need to find difference of two small quantities (1) Can test smaller samples (1) ignore better method/results / more reliable difficult to distinguish between the reading and background (1) grad Total for question = 10 marks