Table II.
Fission Yield of Mo ?? from y235 as a Function of
Bombarding Neutron Energy
Energy (Mev)
0
Percent fission yield 6.142)
-
0.95
6.1018)
4.85
5.45(4)
14.2
5,1 7{®)
(a) 5 Terrell, W. E. Scott, J. S. Gilmore, and C. O. Minkkinen, Phys.
Rev. 92, 1091A (1953).
(b) 5 Terrell, W. E. Scott, J. S. Gilmore, and C.O. Minkkinen, Item 55-
136 (Presented at the American Physical Society Meeting, Sept. 3, 1953,
Albuquerque, New Mexico).
The beta proportional counters (Figure 15) used to determine Mo
99
disintegration rates are calibrated using Pb 210 _ pi?! - Po*!° samples of
known disintegration rates obtained from the National Bureau of Standards.
Pertinent data for each standard are provided by the National Bureau of
Standards.
These Ra D+E samples are counted in the same position relative
to the counter as the Mo’’ 99 is to be counted. A thin (7mg /em*) aluminum
210
4s
from Po }
absorber is placed close to the counter to absorb any a radiations
and B radiations from Pb 210.
The observed counting rate is corrected for
absorption by air gap, absorber, and 3.4 mg /em® aluminum counter window,
back-scattering from the Pd-Ag mount, and self-absorption of the PbO,
electro deposit (see Appendix III for sample calculation).
The corrected
_
counting rate is divided by the known absolute disintegration rate of the standard sample to give the efficiency, i.e., the solid angle of the counter for a
weightless sample mounted on a weightless mounting.
Previously, a carrier-free sample of Mo’ 99 was prepared and a meas- |
ured portion evaporated carefully on a thin Mylar (organic polymer) film
supported on a frame.
Another measured portion of the active solution was
added to a known amountof inactive molybdenum in solution as Mo(VI).
solution was well mixed and heated to 90°C for 15 minutes.
The
Then PbMoO,
was precipitated, washed twice with water, once with acetone, and dried
for one hour at 130°C.
After cooling to room temperature, samples-of vary-
ing weight were prepared on thin aluminum dishes.
All samples were mounted
on thick aluminumholders and counted in the proper geometry.
Figure 16
shows the results of these measurements.
Range
Plii Sg
v
oe
51
A;
}
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