Program - Brookhaven National Laboratory

evaluate radionuclide product yields, impurities, irradiation parameters and wet chemical Re recovery for
a bulk production. We demonstrated that 186 Re can be isolated in 97% yield from irradiated nat WO3
targets within 12 h of end of bombardment (EOB) via an alkaline dissolution followed by anion exchange.
Tungsten (VI) oxide can be easily recycled for recurrent irradiations. A 186 Re batch yield of 42.7 ± 2.2
µCi/µAh (439 ± 23 MBq/C) (with respect to 186 W content) was obtained after 24 h in an 18.5 µA proton
beam. The target entrance energy was determined to be 15.6 MeV, and the specific activity of 186 Re
at EOB was measured to be 1.9 kCi (70.3 TBq)/mmol. Based upon our studies of nat WO3, a target of
enriched 186 WO3 is used in a second experiment; a proton beam of 250 µA for 24h provides a batch volume
of roughly 250 mCi (9.25 GBq) of 186 Re at EOB with a specific activity approaching the theoretical value
of 35kCi/mmol (1295 TBq/mmol) and a superior radionuclidic purity.
Session OA Fission
Thursday March 7, 2013
Room: Met East at 1:30 PM
OA 1 1:30 PM
Monte Carlo Hauser-Feshbach Calculations of Prompt Fission Neutrons and Gamma Rays
P. Talou, T. Kawano, I. Stetcu
Nuclear Physics Group, Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM 87545,
USA
B. Becker
EC-JRC-IRMM, B-2440, Geel, Belgium
Y. Danon
Gaerttner LINAC Laboratory, Rensselaer Polytechnic Institute, NY 12180, USA
Primary fission fragments are perhaps the best example of the formation of compound nuclei, and the
statistical description of their decay within the Hauser-Feshbach (HF) formalism is expected to work quite
well. In the energy regime typical of low-energy fission reactions, the fragments are formed with 15-20 MeV
excitation energy on average, and mostly neutron and gamma-ray evaporations will be contributing to their
de-excitation. The study of these prompt neutrons and gamma rays is very useful from a fundamental point
of view to better understand the mechanisms at play near the point of scission, as well as for practical
applications and signatures of the fission process. We have developed a Monte Carlo Hauser-Feshbach
(MCHF) code, named CGMF, to study the de-excitation of the fission fragments. The Monte Carlo
method provides information on distributions and correlations of the emitted particles, which would be
very cumbersome to extract from standard deterministic approaches. While average quantities such as
the average prompt fission neutron multiplicity and spectrum can be calculated with simpler models, it’s
only by studying distributions and correlations that one can achieve a better physical understanding and
provide new tools for nuclear technologies. We have performed MCHF calculations of the neutron-induced
reactions on 235 U, 239 Pu and spontaneous fission of 252 Cf. We present numerical results for those three
cases and discuss the choice of model input parameters. In particular, the initial excitation energy and
spin distributions of the initial fission fragments are discussed in view of results on the mass-dependent
average neutron multiplicity and gamma-ray emission. The role of collective vs. intrinsic excitation energies
and their distribution between the two fragments is discussed at length. Our conclusion emphasizes the
important role that accurate experimental data could play in differentiating among several theoretical
models of fission.
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