Absolute Beta Counting Using Thick Sources Page: 22
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22
roughly 20 mg/cm^ to about 2$0 Each foil was In
turn activated in the lucite holder at a distance of ^ em
from the Ra-Be neutron source in water* Activations ware
not carried to saturation* however* Instead, an activation
time of $0 minutes was taken a# standard. This short acti-
vation time was selected'so that all eight foils could be
activated and counted during one period of operation* This
procedure was adopted to avoid the necessity of correcting
for-natural day-to-day drift in the counter sensitivity*
Each active foil wag mounted on the "infinite* backing
and counted for a total of !;0 minutes, 23 minutes with each
aide facing the counter tube*. All measurements were corrected
for decay and those for a given foil averaged* The result#
are shown in Table I under the heading Co Thermal, plug
Resonance*
Since our interest was in the activity produced by
thermal neutrons, it was necessary to correct for the activ-
ity produced by the absorption of indium resonance neutrons
(energy at resonance peak — l*ij4 electron volt*3). This
correction was made by re-activating each foil in the cad-
mium holder. The neutron absorption characteristic of cad-
mium is such that it absorbs all thermal neutrons'but prac-
tically none of the indium resonance neutrons. The counting
I. Hoover, W. H. Jordan, C. D. Moak, L. Pardue,
H. Pomerance, J. D. Strong, and E. 0. Wollan, Phys. Rev.,
864 (19it8). —
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Anderson, Miles E., 1926-. Absolute Beta Counting Using Thick Sources, thesis, 1950; Denton, Texas. (https://digital.library.unt.edu/ark:/67531/metadc96872/m1/27/: accessed May 1, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; .