# 1a ii radiation cannot penetrate the paper wrapping

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metal sheets will not turn black. 1A (ii) radiation cannot penetrate the paper wrapping the film. 1A Therefore, none of the parts will be blackened. 1A 26 (a) (i) Gamma 1A (ii) Alpha 1A (iii) Gamma 1A (iv) Beta 1A (b) (i) Light could not reach the film. 1A (ii) It passes through (thick) paper and 1A affects photographic plate. 1A (iii) radiation 1A It cannot pass through paper. 1A (iv) To find out about penetrative properties. 1A 27 (HKCEE 2008 Paper 1 Q12) Experiment questions (p.38) 28 (a) The thickness of the lead block is the independent variable. 1A The count rate is the dependent variable. 1A (b) To ensure that the source aligns with the G-M tube. 1A (c) Keep the sources at arm’s length, and point it away from the human body, especially the eyes. 1A (Or other reasonable answers) 29 (a) Firstly, put away the source and measure the background count rate. Secondly, put the source in front of the G-M tube. Change the distance between the source and the G-M tube from 2 cm to 10 cm. 1A There should be no significant change in the count rate, showing that no radiation is emitted. 1A Put the source a few centimetres in front of the G-M tube. At a position between the G-M tube and the source, arrange the
5 Radioactivity and Nuclear Energy Chapter 3 Nuclear Energy New Senior Secondary Physics at Work (Second Edition) 5 Oxford University Press 2016 lead sheets side by side and leave a narrow gap in front of the source. Then, put the magnets between the lead sheets and the G-M tube, producing a magnetic field pointing downwards. 1A Compare with the count rate of background radiation, there should be no increase in count rate, showing that no radiation is emitted. 1A Move the G-M tube sideways. There should be a position where the count rate is higher than the background count rate. This shows that the source emits radiation. 1A (b) To ensure that the radiation entering the magnetic field travels in one direction. 1A Physics in article (p.39) 30 (a) The pigment in part A absorbs most X-rays. 1A (Or it allows the least X-rays to pass through and reach the film) The X-ray film in this part is blackened the least. 1A (b) White 1A Lead is a kind of metal which can block X-rays from penetrating the painting. 1A

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• Fall '19