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Abstract

A gridded ion chamber is used to determine both the energy (E) of particles emitted from a source positioned coplanar with the cathode, and the cosine of the emission angle (theta') with respect to the normal to the cathode. In the plane defined by the variables cos theta' and E, it is possible to identify an area which is unaffected by particle backscattering and self-absorption. Events belonging to this area show an isotropic angular distribution, which, extrapolated to theta' + z < 90 degrees, yields the true source strength. The above method was investigated using four evaporated 235-UF-4 samples with nominal thicknesses of 15, 75, 300 and 500 mug/cm**2. The obtained source strengths agreed within 0.3 % with the values independently measured by convention allow geometry alpha counting. Good agreement was also observed for measurements on a weak 232-Th source which had a complex energy spectrum. For all the above samples, the source strengths could be determined from alpha particles emitted in solid angles larger than 0.7 x 2pi sterad, which meant a considerably lower counting time than needed for the conventional low geometry counting technique. It is also emphasized that the present method, within reasonable limits, is insensitive to source shape and thickness homogeneity. An intrinsic detector energy resolution of 13 keV was observed for alpha energies of 4.77 MeV, implying a Fano factor smaller than 0.24 for the counter gas CH-4.

Additional information

Authors: BUDTZ JOERGENSEN C, JRC GEEL ESTAB. (BELGIUM);KNITTER H H JRC GEEL ESTAB. (BELGIUM), JRC GEEL ESTAB. (BELGIUM)
Bibliographic Reference: NUCLEAR INSTRUMENTS AND METHODS IN PHYSICS RESEARCH, VOL. 223 (1984), PP. 295-302
Record Number: 1989123032500 / Last updated on: 1987-01-01
Category: PUBLICATION
Available languages: en
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