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 Aug 29th 2008, 08:05 PM #1 Senior Member   Join Date: Apr 2008 Location: HK Posts: 886 Count rate Cound anyone help me with the problem as I am a bit confused about that. Attached Thumbnails
Aug 29th 2008, 08:16 PM   #2
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 Originally Posted by werehk Cound anyone help me with the problem as I am a bit confused about that.
This is essentially a logic problem, not a Physics problem.

The lead will block the most counts, the aluminum will block less, and the cardboard will block the least. So none of the count rates will be the same for any two materials (though see the comment at the end of this post.) So A, D, and E are out.

Also the background count is 50, which no material is going to block, so the smallest count rate is 50. Thus C is out.

This leaves B as the only possibility.

*Note: If the aluminum is sufficient to shield all of the radiation from the source (not likely, but possible) then the count rate for both aluminum and lead will be 50. So option E is possible. So I suppose the most correct answer is B and E. Talk this one over with your instructor.

-Dan
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 Aug 30th 2008, 08:20 PM #3 Senior Member   Join Date: Apr 2008 Location: HK Posts: 886 As the radioactive source only emits alpha and gamma radiation, does it mean that when aluminium sheet is added, there should be no change in count rate so that count rate x and y would be the same?
Aug 31st 2008, 10:35 AM   #4
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 Originally Posted by werehk As the radioactive source only emits alpha and gamma radiation, does it mean that when aluminium sheet is added, there should be no change in count rate so that count rate x and y would be the same?
Gamma radiation will mostly pass through Aluminum, it is true, but any mass placed in front of a source will reduce the rate. So I can't see how x and y would be the same.

-Dan
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