1 - IAEA Nuclear Data Services

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Neutron Capture Cross Sections
H. Weigmann, J. Winter
Capture Cross Sections
The detector [12] for neutron capture cross section
measurements which was described in the last Annual
Progress Report has been used for measurements on
240
natural Mo, Pu, natural Cu, and natural Nd.
Measurements__on_Natural_Mo
Data for natural Mo have been obtained in the neutron
energy range, from 10 eV to 25 keV [13]. An area analysis
which contains a Monte-Carlo subroutine to calculate
the multiple scattering contribution to the
capture areas, has been applied to resonances with
known isotopic assignment; it yields gr for small
resonances and IV for large ones. Above 1 keV neutron
energy, the observed capture rate has been averaged
to give the mean capture cross section which is in
good agreement with earlier measurements. Por the
final attribution and analysis of some resonances to
specific isotopes of Mo, measurements on separated
isotopes are planned.
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Measurements_on Pu
Neutron radiative capture in
240
Pu has been studied
in the neutron energy range from 38 eV to 820 eV [14].
The resonance area analysis of the capture data has
been combined with the transmission area analysis
(see above) to obtain the resonance parameters.
The radiative widths of 32 resonances have been determined
yielding a mean value of = (23.2 _+ 2.0)
meV. The observation of unusual large radiative widths
for some resonances at the upper limit of the analysed
energy range has been interpreted as being due to the
presence of subthreshold fission in these resonances.
This interpretation has been confirmed in a measure-