Program - Brookhaven National Laboratory

Shintaro Hashimoto, Osamu Iwamoto, Yosuke Iwamoto, Tatsuhiko Sato
Japan Atomic Energy Agency, Ibaraki-ken, 319-1195, Japan
Koji Niita
Research Organization for Information Science and Technology, Ibaraki-ken, 319-1196, Japan
Monte Carlo simulation codes such as PHITS, MCNP, FLUKA and MARS play an important role in
prediction of radiation damage to materials and human bodies under irradiation. As these codes can
describe the transport of many particles, e.g. photons, electrons, nucleons, and heavy ions, using various
physical processes, we can obtain deposit energies and particle fluxes in materials for many purposes. In
particular, nuclear reaction processes are essential parts for the production of secondary particles in a high
energy region. Recently, there are plans to utilize accelerator-based neutron sources using the reaction
between proton or deuteron beams and Li, Be or C target for Boron Neutron Capture Therapy (BNCT)
or the material test under irradiation at the International Fusion Materials Irradiation Facility (IFMIF)
project. For neutron source design, evaluation of neutron yields created by nuclear reactions at incident
energies from 10 to 100 MeV is indispensable. However, as nuclear reaction models of the Intra-Nuclear
Cascade type used in most of the simulation codes cannot describe quantum mechanical effects, discrete
neutron peaks in the neutron energy spectrum are neglected. Although the use of the evaluated nuclear
data can give detailed and complex spectra, the energy of the incident particle has been generally limited,
e.g. less than 20 MeV. In this study, we obtain cross sections of the discrete states using the Distorted Wave
Born Approximation (DWBA) method, which is a theoretical model based on quantum mechanics, and
combine the cascade type calculation with the event generator using the DWBA results. This combined
model gives not only a broad peak but also discrete peaks of the neutron spectrum for deuteron induced
reactions on Li, Be, and C targets. We will show results for proton induced reactions on the targets, and
discuss effects of neutron spectra by different nuclear reaction models on the dose estimation.
HC 2 4:00 PM
Calculations of Compound Nucleus Spin-Parity Distributions Populated via the (P,T)
Reaction in Support of Surrogate Reaction Measurements
James Benstead
AWE, UK
Prof Jeff Tostevin
University of Surrey, UK
The surrogate reaction method may be used to determine the cross section for neutron induced reactions
not accessible through standard experimental techniques. This is achieved by creating the same compound
nucleus as would be expected in the desired reaction, but through a different incident channel, generally
a direct transfer reaction. So far, the surrogate technique has been applied with reasonable success to
determine the fission cross section for a number of actinides [1], but has been less successful when applied
to other reactions, e.g. (n,γ), due to a ”spin-parity mismatch” [2]. This mismatch, between the distributions
of the excited levels of the compound nucleus populated in the desired and surrogate channels, leads to
differing decay probabilities and hence reduces the validity of using the surrogate method to infer the cross
section in the desired channel. A greater theoretical understanding of the expected distribution of levels
excited in both the desired and surrogate channels is therefore required in order to attempt to address this
mismatch and allow the method to be utilised with greater confidence. Two neutron transfer reactions,
e.g. (p,t), which allow the technique to be utilised for isotopes further removed from the line of stability,
are the subject of this study. Preliminary results will be presented for calculations of the distribution of
compound nucleus states populated, via the (p,t) reaction, at excitation energies consistent with those
115