Nuclear Geiger Counter Experiment #1
Energy Spectrum of Strontium 90 Beta Radiation Source
We classify the beta energy spectrum as the intensity of a beta beam at different particle energies. Strontium 90 emits two beta energeies, one at 0.546 MeV and the other at 2.28 MeV, see chart below.
Using a .001 brass shield one can separate the 0.56 MeV from the 2.28 MeV beta particles from an SR-90 source. The 0.56 MeV can be blocked using a simple sheild. We can meausre the difference using an accurate CPM count from a geiger counter.
See chart below.
Open Shield | with 1 Mil (.001) Brass Shield | ||||
Sample | Distance | Count CPM | Sample | Distance | Count CPM |
Sample 1 | 2" | 370 | Sample 1 | 2" | 244 |
Sample 2 | " | 400 | Sample 2 | " | 251 |
Sample 3 | " | 403 | Sample 3 | " | 247 |
Sample 4 | " | 382 | Sample 4 | " | 246 |
Sample 1 | 3" | 219 | Sample 1 | 3" | 135 |
Sample 2 | " | 206 | Sample 2 | " | 149 |
Sample 3 | " | 194 | Sample 3 | " | 121 |
Sample 4 | " | 195 | Sample 4 | " | 120 |
Sample 1 | 4" | 127 | Sample 1 | 4" | 77 |
Sample 2 | " | 119 | Sample 2 | " | 98 |
Sample 3 | " | 124 | Sample 3 | " | 87 |
Sample 4 | " | 134 | Sample 4 | " | 82 |
Results
Average CPM with no shield | Average CPM with 1 Mil (.001) Brass Shield | % reduction in measured radiation | |
2" | 404 | 176 | 44% |
3" | 164 | 84 | 51% |
4" | 100 | 55 | 55% |
Copyright 2012
Images SI Inc.
Staten Island NY 10312
Phone: (718) 966-3694
Fax: (718) 966-3695
Strontium 90 Source
Description | Activity | Half-Life | Item# | Price |
---|---|---|---|---|
Strontium-90 |
0.1uCi |
28.5 years |
SR-90-S |
$79.95 |
Primary Radiation Type |
Energies KeV |
Secondary Radiation Type(s) |
||
Beta (β) |
546 |
N/A |
Radioactive isotopes are drop-shipped from a different location & can not be returned or refunded.
SR-90 - $79.95
Strontium 90 Radioactive Source
SH-06 - $9.95
1 Mil Brass Shield for Geiger Counter Wand
.001-Brass - $2.95
1 mill brass sheet 1.5 inches square
Posted Comments
Received Sunday March 31st, 2013
Dear Images,
Nuclear Experiment 1 shows Strontium 90 emitting two beta energies at 0.546 Mev and 2.28 Mev. As shown, placing a 1 mil brass sheet entirely eliminates the 0.546 Mev beta particles from being counted. According to my calculation, the brass sheet would need to be about 7 mils to stop all beta particle at 0.546 Mev.
I dusted off my trusted source Nuclear Reactor Engineering by Samuel Glasstone (1967), pp. 46-47 and used the absorption thickness density formula:
R x rho = 0.54E - 0.15.
R is maximum range of beta particles, rho is the density of absorber (8.5 grams/cm^3 for brass), and E is the maximum energy of the beta particles from the source.
Using this relationship, the brass sheet thickness would need to be 6.7 mils to completely stop the 0.546 Mev beta particles:
R x rho = (0.54)*(0.546) - 0.15 = 0.145
R= 0.145/rho = 0.145/8.5 = 0.017 cm = 0.0067 inches = 6.7 mils.
For 2.28 Mev beta particles, R = ((0.54)*(2.28) - 0.15)/8.5 = 0.1272 cm = 50 mils.
In sum, a 1 mil brass sheet would reduce, but not stop all 0.546 beta particles.
I appreciate your efforts in doing these informative nuclear experiments.
Best,
James Gekas
University Park, MD
Excerpt from Nuclear Reactor Engineering by Samuel Glasstone (PDF 404KB)