169 research outputs found
Spin-dependent observables in surrogate reactions
Observables emitted from various spin states in compound U nuclei are
investigated to validate usefulness of the surrogate reaction method. It was
found that energy spectrum of cascading -rays and their multiplicities,
spectrum of evaporated neutrons, and mass-distribution of fission fragments
show clear dependence on the spin of decaying nuclei. The present results
indicate that they can be used to infer populated spin distributions which
significantly affect the decay branching ratio of the compound system produced
by the surrogate reactions
Large enhancement of radiative strength for soft transisitons in the quasicontinuum
Radiative strength functions (RSFs) for the 56,57-Fe nuclei below the
separation energy are obtained from the 57-Fe(3-He,alpha gamma)56-Fe and
57-Fe(3-He,3-He' gamma)57-Fe reactions, respectively. An enhancement of more
than a factor of ten over common theoretical models of the soft (E_gamma ~< 2
MeV) RSF for transitions in the quasicontinuum (several MeV above the yrast
line) is observed. Two-step cascade intensities with soft primary transitions
from the 56-Fe(n,2gamma)57-Fe reaction confirm the enhancement.Comment: 4 pages including 3 figure
Neutrino Nucleus Reactions based on New Shell Model Hamiltonians
A new shell model Hamiltonian for p-shell nuclei which properly takes into
account important roles of spin-isospin interactions is used to obtain cross
sections of neutrino-^12C reactions induced by decay-at-rest (DAR) neutrinos as
well as supernona neutrinos. Branching ratios to various decay channels are
calculated by the Hauser-Feshbach theory. Neutrino-^4He reactions are also
investigated by using recent shell model Hamiltonians. The reaction cross
sections are found to be enhanced for both ^12C and ^4He compared with previous
calculations. As an interesting consequence of this, a possible enhancement of
the production yields of light elements, ^7Li and ^11B, during supernova
explosions is pointed out.Comment: 11 pages, 14 eps-figures, to be published in Physical Review C (in
press
Astrophysical S-factors for fusion reactions involving C, O, Ne and Mg isotopes
Using the Sao Paulo potential and the barrier penetration formalism we have
calculated the astrophysical factor S(E) for 946 fusion reactions involving
stable and neutron-rich isotopes of C, O, Ne, and Mg for center-of-mass
energies E varying from 2 MeV to 18-30 MeV (covering the range below and above
the Coulomb barrier). We have parameterized the energy dependence S(E) by an
accurate universal 9-parameter analytic expression and present tables of fit
parameters for all the reactions. We also discuss the reduced 3-parameter
version of our fit which is highly accurate at energies below the Coulomb
barrier, and outline the procedure for calculating the reaction rates. The
results can be easily converted to thermonuclear or pycnonuclear reaction rates
to simulate various nuclear burning phenomena, in particular, stellar burning
at high temperatures and nucleosynthesis in high density environments.Comment: 30 pages including 11 tables, 4 figures, ADNDT, accepte
High-precision prompt-γ-ray spectral data from the reaction Pu 241 (nth, f)
In this paper we present results from the first high-precision prompt-γ-ray spectral measurements from the reaction Pu241(nth, f). Apart from one recent experiment, no data are reported in the literature for this fissioning system, which motivated a new dedicated experiment. We have measured prompt-fission γ rays with three cerium-doped LaBr3 (two 5.08cm×5.08 cm and one 7.62cm×7.62 cm) and one CeBr3 (5.08cm×5.08 cm) scintillation detectors, which all exhibit excellent timing and good energy resolution. The average γ-ray multiplicity was determined to be ν̄γ=(8.21±0.09) per fission, the average energy to be εγ=(0.78±0.01) MeV, and the total energy to be Eγ,tot=(6.41±0.06) MeV as the weighted average from all detectors. Since the results from all detectors are in excellent agreement, and the total released γ energy is modestly higher than the one in the present evaluated nuclear data files, we suspect that the underestimation of the prompt-γ heating in nuclear reactors is due to fast-neutron-induced fission on U238 or rather from fission induced by γ rays from neutron capture in the construction material.European Commision NeutAndalus FP7-PEOPLE-2012-CIGPrograma ERINDA 26949
Enhanced radiative strength in the quasi-continuum of 117Sn
Radiative strength functions of 117Sn has been measured below the neutron
separation energy using the (3He,3He'gamma) reactions. An increase in the slope
of the strength functions around E_gamma= 4.5 MeV indicates the onset of a
resonance-like structure, giving a significant enhancement of the radiative
strength function compared to standard models in the energy region 4.5 <=
E_gamma <= 8.0 MeV. For the first time, the functional form of this
resonance-like structure has been measured in an odd tin nucleus below neutron
threshold in the quasi-continuum region.Comment: 4 pages, 3 figure
A structural evaluation of the tungsten isotopes via thermal neutron capture
Total radiative thermal neutron-capture -ray cross sections for the
W isotopes were measured using guided neutron beams from
the Budapest Research Reactor to induce prompt and delayed rays from
elemental and isotopically-enriched tungsten targets. These cross sections were
determined from the sum of measured -ray cross sections feeding the
ground state from low-lying levels below a cutoff energy, E, where
the level scheme is completely known, and continuum rays from levels
above E, calculated using the Monte Carlo statistical-decay code
DICEBOX. The new cross sections determined in this work for the tungsten
nuclides are: b and
b;
b and b; b and
b; and,
b and b. These results are consistent with
earlier measurements in the literature. The W cross section was also
independently confirmed from an activation measurement, following the decay of
W, yielding values for that are consistent
with our prompt -ray measurement. The cross-section measurements were
found to be insensitive to choice of level density or photon strength model,
and only weakly dependent on E. Total radiative-capture widths
calculated with DICEBOX showed much greater model dependence, however, the
recommended values could be reproduced with selected model choices. The decay
schemes for all tungsten isotopes were improved in these analyses.Comment: 25 pages, 15 figures, 15 table
Extraction of thermal and electromagnetic properties in 45Ti
The level density and gamma-ray strength function of 45Ti have been
determined by use of the Oslo method. The particle-gamma coincidences from the
46Ti(p,d gamma)45Ti pick-up reaction with 32 MeV protons are utilized to obtain
gamma-ray spectra as function of excitation energy. The extracted level density
and strength function are compared with models, which are found to describe
these quantities satisfactorily. The data do not reveal any single-particle
energy gaps of the underlying doubly magic 40Ca core, probably due to the
strong quadruple deformation
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New neutron cross section and fission yield data for SNManalysis
Neutron cross-section data are fundamental for the design ofnuclear interrogation systems, the maintenance of nuclear materials andwaste, and the understanding the consequences of nuclear catastrophe.Although a large body of nuclear data exists, it is often old,unreliable, or poorly determined. For several years we have collaborated,as part of an IAEA Coordinated Research Project, to precisely measure thepartial thermal neutron gamma ray cross sections for all elements fromhydrogen to uranium at the Budapest Reactor. These data will replace theunreliable tables of Lone et al [1], still widely in use, and will bepublished as an IAEA TECDOC
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