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APPENDIX F:
Gamma and Beta Dose Rate Data
Gamma Dose Rate Data
Beta Dose Rate Data
Gamma Dose Rate Data (top)
All values are given in mrem/hour for the distances specified. Roentgens
have been converted to rads (soft tissues) and then to rems using a
QF of 1.
a. Gamma dose rates per millicurie for
various gamma energies assuming 1 gamma ray per disintegration:
Photon Energy (MeV) |
Dose Rate (mrem/hr @30cm) |
0.02 |
2.1 |
0.03 |
0.92 |
0.05 |
0.42 |
0.10 |
0.49 |
0.20 |
1.1 |
0.30 |
1.8 |
0.50 |
3.1 |
0.60 |
3.7 |
0.80 |
4.8 |
1.0 |
5.8 |
1.5 |
7.9 |
2.0 |
9.7 |
3.0 |
12.8 |
Adapted from Table A-3 in The Physics of Radiology by H. Johns
and J. Cunningham, Charles C. Thomas, Publisher (1974).
b. Gamma dose rates per millicurie for
some commonly used gamma emitters:
| Radioisotope |
Dose Rate (mrem/hr/mCi)
@30 cm................@100cm |
| Be-7 |
~0.32 |
~0.03 |
| Na-24 |
20 |
1.8 |
| Cr-51 |
0.17 |
0.02 |
| Mn-54 |
5.0 |
0.45 |
| Fe-59 |
6.8 |
0.61 |
| Co-60 |
14 |
1.3 |
| I-125 |
~0.75 |
~0.07 |
| I-131 |
2.3 |
0.21 |
| Cs-137 |
3.5 |
0.32 |
| Hg-203 |
1.4 |
0.12 |
| Ra-226 and daughters |
8.8 |
0.79 |
Adapted from Radiological Health Handbook, 1970 edition.
c. A useful rule of thumb for estimating
the dose rate from a point source gamma emitter:
mrem/hr @ 30 cm = 6 (A)(E);
where A = source activity in millicuries and E = total energy per
disintegration in MeV
Over the energy range 0.07 to 4 MeV this yields a value within + 20%
of the true value.
Beta Dose Rate Data (top)
a. Beta dose rates to skin from a 1 millicurie
unshielded point source, neglecting air absorption:
Maximum Beta Energy (MeV) |
Dose Rate @ 10cm (rem/hr/mCi) |
0.25 |
2.2 |
0.30 |
3.4 |
0.40 |
5.0 |
0.50 |
5.2 |
0.60 |
5.1 |
0.80 |
4.9 |
1.0 |
4.6 |
1.5 |
4.0 |
2.0 |
3.6 |
From "Rough Estimates of Beta Doses to the Skin" by
W.G. Cross, Health Physics, 11 (453), 1965.
b. A useful rule of thumb for estimating
the skin dose rate from a beta particle emitter (assuming one beta particle
per disintegration):
The dose rate from an unshielded point source is 5 rem/hour/millicurie
at 10 cm.
This yields values good to within a factor of two, for beta emitters
with a maximum beta energy greater than 300 KeV.
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