Verlag des Forschungszentrums Jülich
JUEL-3980
Reimer, Peter
Fast neutron induced reactions leading to activation products
IX, 103 S., 2002
Neutron induced cross sections are of interest for practical applications and for testing
nuclear models. In this work (n,p), (n,np), (n,α;), (n,nα;), (n,n'γ), (n,2n) and (n,3n)
reactions on vanadium, molybdenum, technetium and lead have been measured in the
energy range of 0.5 to 20.6 MeV using the activation technique. The radioactive reaction
products with half-lives between 58 seconds and 20300 years have been measured offline
via high-resolution γ-ray-spectrometry and Liquid Scintillation Counting, the latter in
combination with radiochemical separation.
Irradiations with neutron energies in the range of 0.5 to 6 Me V were done using
the 3H(p,n)3He reaction with a solid-state Ti/T target while energies between 7.4 and
12.5 MeV were covered with the 2H(d,n)3He reaction utilizing a D2 gas target. Irradiations
in the energy range from 13.4 to 20.6 MeV were performed using the 3H(d,n)4He reaction,
again with a solid Ti/T target. Most of the reactions were investigated using a light mass
setup to minimise scattering effects, but for short half-lives a pneumatic sample transport
system was used as well. A special sample holder was developed for the measurement of
the natMo(n,x)94Nb reaction.
All cross sections were measured relative to the 27 Al(n,α)24Na standard cross section
and all necesarry corrections due to the irradiation process and the measurement of the
induced activity have been applied.
Nuclear model calculations were performed for all investigated reactions. For reactions
on 99Tc and Pb the original STAPRE code was used, while for reactions on V and Mo a
modified version STAPRE-H was employed.
As a result of this thesis work an extended database for neutron induced cross sections
on four elements was obtained. It was possible to establish first excitation functions for
reactions on a radioactive target nucleus, one very long-lived product and one purely β-
emitting product. It was found that existing evaluations are not always reliable in the
prediction of unknown cross sections. Although the experimental results of this work
helped to considerably improve the calculations, some deficiencies still exist in case of
complex particle emission (like d,t,α) and second chance emission (n,np) or (n,pn) etc.
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