41 research outputs found
MCNP6 Study of Fragmentation Products from 112Sn + 112Sn and 124Sn + 124Sn at 1 GeV/nucleon
Isotope production cross sections from 112Sn + 112Sn and 124Sn + 124Sn
reactions at 1 GeV/nucleon, which were measured recently at GSI using the
heavy-ion accelerator SIS18 and the Fragment Separator (FRS), have been
analyzed with the latest Los Alamos Monte-Carlo transport code MCNP6 using the
LAQGSM03.03 event generator. MCNP6 reproduces reasonably well all the measured
cross sections. Comparison of the MCNP6 results with the measured data and with
calculations by a modification of the Los Alamos version of the Quark-Gluon
String Model allowing for multifragmentation processes in the framework of the
Statistical Multifragmentation Model (SMM) by Botvina and coauthors, as
realized in the code LAQGSM03.S1, does not suggest unambiguous evidence of a
multifragmentation signature.Comment: 3 pages, 2 figures, Proc. 2013 International Conference on Nuclear
Data for Science & Technology (ND2013), March 4-8, 2013, New York, USA, to be
published in Nuclear Data Sheet
CEM2k - Recent Developments in CEM
Recent developments of the Cascade-Exciton Model (CEM) of nuclear reactions
are briefly described. These changes are motivated by new data on isotope
production measured recently in "reverse kinematics" at GSI for interactions of
208-Pb and 238-U at 1 GeV/nucleon and 197-Au at 800 MeV/nucleon with liquid
1-H. This study leads us to CEM2k, which is a new version of the CEM code that
is still under development. The increased accuracy and predictive power of the
code CEM2k are shown by several examples. Further necessary work is outlined.Comment: 14 pages, 8 figures, 1 table, LaTeX, submitted to Proc. 2000 ANS/ENS
International Meeting, Nuclear Applications of Accelerator Technology
(AccApp00), November 12-16, Washington, DC, US
Modeling Fission in the Cascade-Exciton Model
Recent developments of the Cascade-Exciton Model (CEM) of nuclear reactions
to describe high energy particle induced fission are briefly described. The
increased accuracy and predictive power of the CEM are shown by several
examples. Further necessary work is outlined.Comment: 15 pages, 5 figures, LaTeX, Talk given at the Fourth Workshop on
Simulating Accelerator Radiation Environments (SARE4), Knoxville, Tennessee,
September 14-16, 199
Improved Cascade-Exciton Model of Nuclear Reactions
Recent improvements to the Cascade-Exciton Model (CEM) of nuclear reactions
are briefly described. They concern mainly the cascade stage of reactions and a
better description of nuclei during the preequilibrium and evaporation stages
of reactions. The development of the CEM concerning fission is given in a
separate talk at this conference. The increased accuracy and predictive power
of the CEM are shown by several examples. Possible further improvements to the
CEM and other models are discussed.Comment: 23 pages, 12 figures, LaTeX, Talk given at the Fourth Workshop on
Simulating Accelerator Radiation Environments (SARE4), Knoxville, Tennessee,
September 14-16, 199
The character and prevalence of third minima in actinide fission barriers
The double-humped structure of many actinide fission barriers is well
established both experimentally and theoretically. There is also evidence, both
experimental and theoretical, that some actinide nuclei have barriers with a
third minimum, outside the second, fission-isomeric minimum. We perform a
large-scale, systematic calculation of actinide fission barriers to identify
which actinide nuclei exhibit third minima. We find that only a relatively few
nuclei accessible to experiment exhibit third minima in their barriers,
approximately nuclei with proton number in the range
and nucleon number in the range . We find that the
third minimum is less than 1 MeV deep for light Th and U isotopes. This is
consistent with some previous experimental and theoretical results, but differs
from some others. We discuss possible origins of these incompatible results and
what are the most realistic predictions of where third minima are observable
Merging the CEM2K and LAQGSM Codes with GEM2 to Describe Fission and Light-fragment Production
We present the current status of the improved Cascade-Exciton Model (CEM)
code CEM2k and of the Los Alamos version of the Quark-Gluon String Model code
LAQGSM. To describe fission and light-fragment (heavier than He4) production,
both CEM2k and LAQGSM have been merged with the GEM2 code of Furihata. We
present some results on proton- and deuteron-induced spallation, fission, and
fragmentation reactions predicted by these extended versions of CEM2k and
LAQGSM. We show that merging CEM2k and LAQGSM with GEM2 allows us to describe
many fission and fragmentation reactions in addition to the spallation
reactions which are already relatively well described. Nevertheless, the
standard version of GEM2 does not provide a completely satisfactory description
of complex particle spectra, heavy-fragment emission, and spallation yields,
and is not yet a reliable tool for applications. We conclude that we may choose
to use a model similar to the GEM2 approach in our codes, but it must be
significantly extended and further improved. We observe that it is not
sufficient to analyze only A and Z distributions of the product yields when
evaluating this type of model, as is often done in the literature; instead it
is important to study all the separate isotopic yields as well as the spectra
of light particles and fragments.Comment: 33 pages, LaTeX, 16 figures, talk given at the SATIF-6 Meeting, SLAC,
Menlo Park, CA, USA, April 10 - 12, 200
MCNP6 Fission Cross Section Calculations at Intermediate and High Energies
MCNP6 has been Validated and Verified (V&V) against intermediate- and
high-energy fission cross-section experimental data. An error in the
calculation of fission cross sections of 181Ta and a few nearby target nuclei
by the CEM03.03 event generator in MCNP6 and a "bug: in the calculation of
fission cross sections with the GENXS option of MCNP6 while using the
LAQGSM03.03 event generator were detected during our V&V work. After fixing
both problems, we find that MCNP6 using CEM03.03 and LAQGSM03.03 calculates
fission cross sections in good agreement with available experimental data for
reactions induced by nucleons, pions, and photons on both subactinide and
actinide nuclei at incident energies from several tens of MeV to about 1 TeV.Comment: 3 pages, 3 figures, Proc. 2013 International Conference on Nuclear
Data for Science & Technology (ND2013), March 4-8, 2013, New York, USA, to be
published in Nuclear Data Sheet
Hauser-Feshbach fission fragment de-excitation with calculated macroscopic-microscopic mass yields
The Hauser-Feshbach statistical model is applied to the de-excitation of
primary fission fragments using input mass yields calculated with
macroscopic-microscopic models of the potential energy surface. We test the
sensitivity of the prompt fission observables to the input mass yields for two
important reactions, U and
Pu, for which good experimental data exist. General
traits of the mass yields, such as the location of the peaks and their widths,
can impact both the prompt neutron and -ray multiplicities, as well as
their spectra. Specifically, we use several mass yields to determine a linear
correlation between the calculated prompt neutron multiplicity and
the average heavy-fragment mass of the input mass yields
. The
mass peak width influences the correlation between the total kinetic energy of
the fission fragments and the total number of prompt neutrons emitted
. Typical biases on prompt particle observables from
using calculated mass yields instead of experimental ones are: for the average prompt neutron multiplicity, for the average prompt -ray multiplicity, for the average outgoing neutron energy,
for the average -ray energy, and
for the average total kinetic
energy of the fission fragments.Comment: 12 pages, 8 figures, 2 table
Comparison of Expanded Preequilibrium CEM Model with CEM03.03 and Experimental Data, FY2013
Emission of light fragments (LF) from nuclear reactions is an open question.
Different reaction mechanisms contribute to their production; the relative
roles of each, and how they change with incident energy, mass number of the
target, and the type and emission energy of the fragments is not completely
understood.
None of the available models are able to accurately predict emission of LF
from arbitrary reactions. However, the ability to describe production of LF
(especially at energies MeV) from many reactions is important for
different applications, such as cosmic-ray-induced Single Event Upsets (SEUs),
radiation protection, and cancer therapy with proton and heavy-ion beams, to
name just a few. The Cascade-Exciton Model (CEM) version 03.03 and the Los
Alamos version of the Quark-Gluon String Model (LAQGSM) version 03.03 event
generators in Monte Carlo N-Particle Transport Code version 6 (MCNP6) describe
quite well the spectra of fragments with sizes up to He across a broad
range of target masses and incident energies (up to GeV for CEM and up
to TeV/A for LAQGSM). However, they do not predict the high-energy
tails of LF spectra heavier than He well. Most LF with energies above
several tens of MeV are emitted during the precompound stage of a reaction. The
current versions of the CEM and LAQGSM event generators do not account for
precompound emission of LF larger than He.
The aim of our work is to extend the precompound model in them to include
such processes, leading to an increase of predictive power of LF-production in
MCNP6. Extending our models to include emission of fragments heavier than
He at the precompound stage has already provided preliminary results that
have much better agreement with experimental data
Preequilibrium Emission of Light Fragments in Spallation Reactions
The ability to describe production of light fragments (LF) is important for
many applications, such as cosmic-ray-induced single event upsets (SEUs),
radiation protection, and cancer therapy with proton and heavy-ion beams. The
Cascade-Exciton Model (CEM) and the Los Alamos version of the Quark-Gluon
String Model (LAQGSM) event generators in the LANL transport code MCNP6,
describe quite well the spectra of fragments with sizes up to 4He across a
broad range of target masses and incident energies (up to ~ 5 GeV for CEM and
up to ~ 1 TeV/A for LAQGSM). However, they do not predict the high-energy tails
of LF spectra heavier than 4He well. Most LF with energies above several tens
of MeV are emitted during the precompound stage of a reaction. The current
versions of our event generators do not account for precompound emission of LF
larger than 4He. The aim of our work is to generalize the precompound model to
include such processes, leading to increased predictive power of LF production.
Extending the model in this way provides preliminary results that have much
better agreement with experimental data.Comment: 3 pages, 4 figures, Proc. 2013 International Conference on Nuclear
Data for Science & Technology (ND2013), March 4-8, 2013, New York, USA, to be
published in Nuclear Data Shee