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A radioactive source produces gamma rays - OCR Gateway - GCSE Physics - Question 7 - 2021 - Paper 1
Question 7
A radioactive source produces gamma rays. The diagram shows a detector and a piece of lead placed near the radioactive source. The count rate is 1840 counts per mi... show full transcript
Worked Solution & Example Answer:A radioactive source produces gamma rays - OCR Gateway - GCSE Physics - Question 7 - 2021 - Paper 1
Step 1
What could the count rate be with the lead in place?
Answer
The lead effectively absorbs gamma rays, reducing the count detected by the counter. Given that the original count rate is 1840 cpm without lead, and considering how lead blocks gamma radiation:
- It is possible that some gamma rays will still pass through the lead, allowing for a lower count rate.
- The lead is likely to significantly decrease the count rate, but not eliminate it completely. Hence, 0 cpm is unlikely.
- The remaining options (160 cpm, 1840 cpm, and 2530 cpm) are assessed. Since the count can only decrease with the lead, the most plausible count rate with the lead in place would be 160 cpm.
Thus, the answer is B) 160 cpm.