Exam-style question
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Which experimental observation would indicate that a radioactive source emits alpha particles rather than beta particles?.
- A.The count rate is unchanged when a sheet of paper is inserted.
- B.The count rate drops to zero when a sheet of paper is inserted.
- C.The count rate increases when a sheet of paper is inserted.
- D.The count rate fluctuates randomly with paper thickness.
Model answer
What a good answer should say
- The count rate drops to zero when a sheet of paper is inserted.
Explanation
Why this works
Alpha particles are stopped by very thin materials such as paper. In an absorption experiment, inserting a sheet of paper between the source and detector will completely block alpha particles, causing the count rate to fall to zero.
Beta particles, being lighter, can penetrate paper, so the count rate would not drop to zero.
Common mistake
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