Program - Brookhaven National Laboratory

DF 2 4:00 PM
Determination of (n,γ) Cross Sections of 241 Am by PGAA
M. Rossbach, C. Genreith
Institute for Energy and Climate Research, IEK-6, Forschungszentrum Jülich GmbH, 52425 Jülich,
Germany
T. Belgya
Nuclear Analysis and Radiography Department, Centre for Energy Research, Hungarian Academy of
Sciences, H-1525 Budapest 114, P.O. Box 49, Hungary
Z. Revay
FRM II, Technische Universität München, Lichtenbergstr. 1, 85747 Garching, Germany
B. W. Sleaford, J.E. Escher
Lawrence Livermore National Laboratory, Livermore, CA 94551
Accurate cross section data of actinides are crucial for criticality calculations of GEN IV reactors and
transmutation but also for analytical purposes such as nuclear waste characterization, decommissioning of
nuclear installations and safeguard applications. Tabulated data are inconsistent and sometimes associated
with large uncertainties. In beam techniques, like prompt gamma activation analysis (PGAA) using
external neutron beams from high flux reactors offer a chance for determination of absolute partial gamma
ray production cross sections with a minimum of uncertainty to around 2 to 3%. Comparative experiments
have been conducted at two independent research reactors to investigate the potential of PGAA for accurate
cross section determination of actinides using well prepared 241 Am sources. Preparation of samples
for irradiation at the Budapest Reactor and FRM II in Garching of the Am sources has been optimized together
with PTB in Braunschweig. Samples were irradiated together and without flux monitors to extract
the relevant nuclear data after appropriate corrections for self-absorption and attenuation of neutrons in
the sample holder. Experimental parameters and results will be presented and discussed. This work was
supported by the Federal Ministry for Education and Research, BMBF, Germany
DF 3 4:20 PM
Impact of Prompt-Neutron Corrections on Final Fission-Fragment Distributions
A. Al-Adili, S. Pomp
Division of Applied Nuclear Physics, Uppsala University, S-751 20 Uppsala, Sweden
F.-J. Hambsch, S. Oberstedt
European Commission, Joint Research Centre IRMM, B-2440 Geel, Belgium
The determination of post-neutron fragment yields has a great impact on the reliable assessment of the
nuclear waste inventory and on the correct prediction of delayed neutron pre-cursor yields. A large number
of fission yields, included in evaluated nuclear data libraries, were measured without the knowledge on the
neutron emission as a function of fragment mass ¯ν(A). Instead, ¯ν(A) had to be parametrized based on a
few known reactions on e. g. 233,235 U and 239 Pu. The prompt neutron multiplicity is a crucial quantity
in nuclear fission and is a function of mass, TKE and incident neutron energy, ν(A, T KE, En). Although
it is well known that the total number of prompt fission neutrons, ¯νtot, increases with incident neutron
energy, the enthralling question has always been, how the additional excitation energy is shared between
the fission fragments. Traditionally, the excess neutrons are assumed to be distributed equally across the
mass distribution. But a few experiments have shown that the extra neutrons are exclusively emitted by
the heavy fragments [1, 2]. Recently, several theoretical works tried to explain these observations [3-5].
For instance, in the ”energy-sorting” process proposed in Ref. [4], the heavy fragment is assumed to have
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