i State two sources of the background radiation 2 marks ii Why the two readings

I state two sources of the background radiation 2

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(i) State two sources of the background radiation. (2 marks) (ii) Why the two readings for each absorber are not identical? (1 mark) (iii) Explain why the results show that the source emits radiation only. (4 marks) (iv) After removing the absorbers and placing an ordinary magnet in front of the source, the count rate decreases to the background count rate. Explain how this result further confirms that the source emits radiation only. (3 marks) (b) The following figure shows a type of badge used by radiation workers. The photographic film is enclosed in a thin light-proof packet. If the badge exposes to excessive radiation, the film would become dark after being developed. (i) Describe the appearance of the developed film if a radiation worker has received an excessive amount of (1) radiation, (1 mark) (2) radiation. (1 mark) (ii) Explain why the film is enclosed in a thin light-proof packet. (1 mark) -- ans --
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2013bb55b04d646e983cd79e8dc8c4edd08a1b7a.doc Solutions Marks (a) (i) Any two of the following: Cosmic rays from outer space Natural radioactive substances in living bodies, and food and drinks Radioactive gases given off from rocks, soil and building materials (Or other reasonable answers) 2 1A (ii) This is because radiation from a radioactive source is emitted at random. 1A (iii) radiation can be stopped by a piece of paper, radiation can be stopped by 5 mm of aluminium, and radiation can be partially absorbed by 10 mm of lead. 1A Compared with the count rate without using absorbers, the count rates do not change a lot when a sheet of paper is inserted. Therefore, the source does not emit radiation. 1A The count rates drop significantly to the background count rate when 5 mm of aluminium is inserted. Therefore, the source emits radiation. 1A If the source also emits radiation, the count rate should be greater than the background count rate when 5 mm of aluminium is inserted. 1A Therefore, the source emits only radiation. (iv) Since radiation is neutral, it would not be deflected in a magnetic field. 1A Moreover, particles would not be deflected much by an ordinary magnet because they have large mass. 1A Only radiation can be deflected by an ordinary magnet and hence the count rate drops. 1A The observation fits the analysis above and confirms that the source emits radiation. (b) (i) (1) Only region P would be dark. 1A (2) The whole film would be dark. 1A (ii) The film is enclosed in a thin light-proof packet to ensure that the darkening of the film is due to radiation but not light. 1A
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2013bb55b04d646e983cd79e8dc8c4edd08a1b7a.doc -- ans end -- {{<P=51><C=01><S=core><T=LQ><M=10><L=3><X=F><id=005>}} 5113005  F (a) The following figure shows the tracks produced by a radioactive source in a cloud chamber. (i) Describe briefly the appearance of the tracks. (2 marks) (ii) What type(s) of radiation does the source emit? (1 mark) (iii) The tracks have about the same length. What characteristics of the radiation does it show? (1 mark) (iv) Sketch the tracks if a very strong magnetic field pointing into the paper is applied to the chamber. (2 marks) (b) Another radioactive source is placed in front of a G-M counter. The count
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  • Summer '14
  • Radioactive Decay, Radioactive contamination, 10 mm, 20 cm, 25 mm, Background radiation

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