Program - Brookhaven National Laboratory

Nuclear Data Section, International Atomic Energy Agency, Vienna, Austria
M. Herman
National Nuclear Data Center, Brookhaven National Laboratory, Upton NY, USA
M. E. Rego
Instituto de Pesquisas Energéticas/CNEN, São Paulo SP, Brazil
Griffin’s exciton model [1] of pre-equilibrium emission and Blann’s hybrid model [2] have proven extremely
successful in describing the energy dependence and, to a certain extent, the angular dependence of nucleon
and composite particle emission in pre-equilibrium reactions. However, the conceptual basis of these
models was called into question by Bisplinghoff already some time ago [3]. In response to Bisplinghoff,
Blann proposed the hybrid Monte Carlo simulation model (HMS) [4], which uses only the densities of
available states for creation and decay of single particle-hole pairs. An additional advantage of the HMS
model compared to earlier ones is that it easily permits multiple emissions from the precompound nucleus.
The model was later extended, in collaboration with Chadwick, to the double-differential HMS [5]. This
extension is based on the Chadwick-Obloˇzinsk´y prescription for approximating the energy-angular distribution
of available two-particle-one-hole states [6,7]. We have recently developed a Monte Carlo algorithm
to calculate this distribution exactly [8]. The Monte Carlo decay algorithm used by Blann and Chadwick
does not permit the calculation of exclusive cross sections because it does not take into account the relative
rate of decay of the particle-hole pairs produced in the excitation process. We show how the algorithm
can be easily modified to take these into account [9] and develop expressions that permit the calculation
of total (precompound + compound) exclusive cross sections. Calculations within the exclusive double
differential HMS model using either approximate or exact energy-angular distributions can be performed
using the nuclear reaction model code EMPIRE-3.1 (Rivoli) [10].
[1] J. J. Griffin, Phys. Rev. Lett. 17 (1966) 57. [2] M. Blann, Phys. Rev. 21 (1968) 1357. [3] J.
Bisplinghoff, Phys. Rev. C 33 (1986) 1569. [4] M. Blann, Phys. Rev. C 54 (1996) 1341. [5] M. Blann and
M. B. Chadwick, Phys. Rev. C 57 (1998) 233. [6] M. B. Chadwick and P. Obloˇzinsk´y, Phys, Rev. C 46
(1992) 2028. [7] M. B. Chadwick and P. Obloˇzinsk´y, Phys, Rev. C 50 (1994) 2490. [8] B. V. Carlson and
D. F. Mega, EPJ Web of Conferences 21, 09001 (2012). [9] C. A. Soares Pompéia and B. V. Carlson, Phys.
Rev. C 74 (2006) 054609. [10] M. Herman, R. Capote, M. Sin, A. Trkov, B. V. Carlson, P. Obloˇzinsk´y,
C. Matoon, H. Wienke, S. Hoblit, Young-Sik Cho, V. Plujko, V. Zerkin, EMPIRE-3.1, available online at
http://www.nndc.bnl.gov/empire/.
BC 4 11:40 AM
EMPIRE: A Reaction Model Code for Nuclear Astrophysics
A. Palumbo, M. Herman
National Nuclear Data Center, BNL, Bldg. 197D, Upton, NY 11973-5000, USA
R. Capote
Nuclear Data Section IAEA, PO Box 100, Wagramer Strasse 5, A-1400 Vienna, Austria
The nuclei heavier than Fe/Ni are mainly synthesized via neutron capture reactions. For the s-process,
cross sections are normally measured via the activation and TOF technique. There have been experimental
deterrents in precisely determining the peak (and/or measurements are over a restricted range) and data
has been normalized using cross sections from evaluated libraries. Unlike the s-process, the r-process path
lies far from stability and is a complex reaction path described by a huge network involving several thousand
reactions (of importance in determining the upper end of the nucleosynthesis flow, the superheavy elements
(SHE) require an accurate fission topology (i.e. fission barriers) [1]). The cross sections of 186,187,188 Os(n,γ),
64,68,70 Zn(n,γ), 197 Au(n,γ), 244 Cm(n,f), 232 Th(n,γ),(n,f) and 233 U(n,f) are calculated using EMPIRE [2] to
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