1 - IAEA Nuclear Data Services
1 - IAEA Nuclear Data Services
1 - IAEA Nuclear Data Services
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homogeneity of the layers. Satisfactory results<br />
(probably accurate within 0.3%) are found for the<br />
comparison of direct weighing in vacuum and relative<br />
neutron measurements for layer thicknesses between<br />
2<br />
about 20 and 80 v-g/cm . These layers will be used<br />
as standards for fission cross-section measurements.<br />
Intercomparison of Fissile Layers<br />
The same equipment as used for the boron comparisons<br />
is used for the intercomparison of fissile layers.<br />
In this case the fission- and a-particle pulse-height<br />
spectra are recorded with beam-on and beam-off. The<br />
fission- and a-counting rates are deduced respectively<br />
per monitor count and per unit-time. The ratios of aand<br />
fission counting-rates can be compared. With nonhomogeneous<br />
sources they may differ.<br />
Measurements were performed on electro-sprayed uranylacetate<br />
sources and evaporated UF¿,-layers made from<br />
NBS-930 ^U-material and agreement was found within<br />
statistical errors proving their good homogeneity.<br />
Another method to compare the quality of the foils<br />
from different preparation methods is to compare the<br />
fission spectrum characteristics of foils with the<br />
same thickness in the same geometry. A particularly<br />
sensitive parameter, e.g., is the ratio Nj- / N-y of<br />
the light fragment peak counting-rate to the valley<br />
counting-rate. From these spectra also the low energy<br />
tailing can be evaluated and possible multiplication<br />
effects (at the high energy-side of the spectrum) of<br />
the surface-barrier detector used can be detected.<br />
They also enabled us to determine the limit thickness<br />
of applicability of the preparation methods to be more<br />
2<br />
than 500 ug/cm for electrosprayed and probably more<br />
than 1 mg/cm<br />
2<br />
for evaporated sources.<br />
2200 m/s Fission Cross-Sections<br />
The boron standard foils and the evaporated ^UF.-