-13-
UCRL- 6252
was placed between the sample and crystal to remove beta particles and to
reduce effects of bremsstrahlung.
Radiations from all nuclides were counted
in this way except those from sro? pq lO? pall, and agi] t,
In the last
four cases beta particles were counted using a methane proportional counter,
and self- scattering and self-absorption corrections were made.
Brems strahl-
ung from y?! was counted on the gross gamma counter described above,
since
the amounts of y’) were large enough to produce satisfactory counting rates.
The outputs of all scalers were attached to an IBM card-punching ma-_
chine,
and data were automatically punched out as the individual count was
completed.
Data were taken over a period of three half-lives, with at least
four counts taken in any given half-life.
This procedure was not practical,
however, with Cs 136,137,
}
here, at least 20 counts were taken over a period
of 4 weeks, the csi activity allowed to decay to less than 1% of the Cs
activity, and 5 more counts taken.
137
When the data were complete the decay
curves of the individual samples were analyzed by a least- squares method
using the IBM 650 computer.
The answers from the computer gave counting
rates of each isotope corrected for decay (both during and after bombardment),
chemical yield,
aliquot,
and seli- scattering and self-absorption.
The R values of Sec. II can be rewritten as follows:*
R,
,
=
(C./C,99) for any type of fission
(C,/C,,,99) for U435 thermal neutron fission
;
where Cc. is the corrected counting rate of nuclide i in its standard geometry
and CM ?? is the corresponding value for Mo?’?,
The value of the denominator
was measured for each nuclide in a series of calibration bombardments of
U
235.
with thermal neutrons.
,
.
In sucha ratio, the proportionality constant be-
tween counting rate (corrected for decay during bombardment) ina standard
geometry
"f
ig
s4
SCOTaty
ield appears both in the numerator and the denominator.
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