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UCRL- 6252
The R values given include corrections for the fact that the nye Fu
target contained a small percentage of uy and the ny? 38 i target (normal
uranium) contained a small percentage of ue?
isotopes were negligible.)
(Contributions from other
In order to make this correction it was assumed
that both targets in a given run were exposed to identical neutron fluxes.
This probably was not strictly true, but the corrections in all cases ‘except
orie were less than 3% and the possible contribution to the overall error was
negligible.
Cs
136
The exceptional case was the measurementof the R values of
oe
7238
formed by fission of U~
,
.
,
which were an order of magnitude lower
than those arising from the fission of ue? with the same neutron spectra.
Therefore the contribution of cs7® from the fission of the y*?° present in
natural uranium was a significant portion of the total csi36 formed in the
bombardment.
Because of the size of these corrections, we have assigned
somewhat larger standard deviations to the final R values of cst 3© from y238
fission.
In those cases where more than one bombardment was made using the
same neutron source, certain activity ratios gave evidence that the flux
profile was not always identical in all bombardments with the same neutron
source.
This being so, it is possible that there may have been some variation
in the energy spectra between different runs with the same neutron source.
Because of this we have treated the results of each bombardmentas individual pieces of data rather than averaging the results from repeated runs.
Experience with many similar radiochemical determinatidns led us to
expect an overall reliability of 5% for the R values in Tables Iand Il.
was borne out on comparison of the results of ''repeated'"' runs.
This
As we have
pointed out, there was evidence to indicate that "repeat'' runs were not strictly
identical with regard to flux profile and possibly energy spectrum.
9001906
However,