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Exponential Attenuation


Materials used:


Setup:
The radium watch-hand was mounted on a small piece of wood, using glue. It was set up facing the window of the GM-45, with a spacing of about half an inch.

Experiment:
The CPM were measured with nothing in the gap between the source and detector, as well as with varying numbers of sheets of paper. Each reading was averaged for approximately 10 minutes, to help reduce statistical variations.

Results:
Here is a table of the measured CPM vs the number of sheets of paper:

Sheets     CPM
0          30335
1          26878
2          23868
3          21680
4          19814
5          18004
6          16344
7          15093
8          13908
9          12920
10         11835
11         10934
12         10220
13          9551
14          8839
15          8299
16          7733
17          7318

And here is a graph of the resulting data. The dark blue line is the data, the purple line is an attempt at an exponential fit. The fit isn't perfect for several reasons, namely that radium and daughter products emit several types of radiation, including several peak beta energies, and the attenuation of beta sources is not purely exponential, due to energy softening effects.



Thinking of buying a surplus CDV-700 or 715 detector? Be sure to read our report first.