47 research outputs found
Montecarlo Calculations for the Moderator of the Pulsed Neutron Target of the Geel Linac. EUR 5157.
Measurement of direct neutron capture by neutron-rich sulfur isotopes
Thermal neutron capture cross sections for S(n,)S and
S(n,)S have been measured and spectroscopic factors of
the final states have been extracted. The calculated direct-capture cross
sections reproduce the experimental data.Comment: 4 pages (uses espcrc1.sty), 1 postscript figure (uses psfig),
accepted for publication in Nucl. Phys. A (Suppl.), uuencoded tex-files and
postscript-files available at ftp://is1.kph.tuwien.ac.at/pub/ohu/Stherm.u
Parity Violation in Neutron Capture Reactions
In the last decade, the scattering of polarized neutrons on compound nucleus
resonances proved to be a powerful experimental technique for probing nuclear
parity violation. Longitudinal analyzing powers in neutron transmission
measurements on p-wave resonances in nuclei such as La and Th
were found to be as large as 10%. Here we examine the possibilities of carrying
out a parallel program to measure asymmetries in the ) reaction on
these same compound nuclear resonances. Symmetry-violating ) studies
can also show asymmetries as large as 10%, and have the advantage over
transmission experiments of allowing parity-odd asymmetries in several
different gamma-decay branches from the same resonance. Thus, studies of parity
violation in the reaction using high efficiency germanium
detectors at the Los Alamos Lujan facility, for example, could determine the
parity-odd nucleon-nucleon matrix elements in complex nuclei with high
accuracy. Additionally, simultaneous studies of the E1 and matrix
elements invol ved in these decays could be used to help constrain the
statistical theory of parity non-conservation in compound nuclei.Comment: 10 pages, 1 figur
Measurement of neutron capture on Ca at thermal and thermonuclear energies
At the Karlsruhe pulsed 3.75\,MV Van de Graaff accelerator the thermonuclear
Ca(n,)Ca(8.72\,min) cross section was measured by the
fast cyclic activation technique via the 3084.5\,keV -ray line of the
Ca-decay. Samples of CaCO enriched in Ca by 77.87\,\% were
irradiated between two gold foils which served as capture standards. The
capture cross-section was measured at the neutron energies 25, 151, 176, and
218\,keV, respectively. Additionally, the thermal capture cross-section was
measured at the reactor BR1 in Mol, Belgium, via the prompt and decay
-ray lines using the same target material. The
Ca(n,)Ca cross-section in the thermonuclear and thermal
energy range has been calculated using the direct-capture model combined with
folding potentials. The potential strengths are adjusted to the scattering
length and the binding energies of the final states in Ca. The small
coherent elastic cross section of Ca+n is explained through the nuclear
Ramsauer effect. Spectroscopic factors of Ca have been extracted from
the thermal capture cross-section with better accuracy than from a recent (d,p)
experiment. Within the uncertainties both results are in agreement. The
non-resonant thermal and thermonuclear experimental data for this reaction can
be reproduced using the direct-capture model. A possible interference with a
resonant contribution is discussed. The neutron spectroscopic factors of
Ca determined from shell-model calculations are compared with the values
extracted from the experimental cross sections for Ca(d,p)Ca and
Ca(n,)Ca.Comment: 15 pages (uses Revtex), 7 postscript figures (uses psfig), accepted
for publication in PRC, uuencoded tex-files and postscript-files also
available at ftp://is1.kph.tuwien.ac.at/pub/ohu/Ca.u
Neutron-induced nucleosynthesis
Neutron--induced nucleosynthesis plays an important role in astrophysical
scenarios like in primordial nucleosynthesis in the early universe, in the
s--process occurring in Red Giants, and in the --rich freeze--out and
r--process taking place in supernovae of type II. A review of the three
important aspects of neutron--induced nucleosynthesis is given: astrophysical
background, experimental methods and theoretical models for determining
reaction cross sections and reaction rates at thermonuclear energies. Three
specific examples of neutron capture at thermal and thermonuclear energies are
discussed in some detail.Comment: 40 pages (uses kluwer.sty), 2 postscript figures (uses psfig),
accepted for publication in Surveys in Geophysics, uuencoded tex-files and
postscript-files available at ftp://is1.kph.tuwien.ac.at/pub/ohu/Geo.u
On the figure of merit in neutron time-of-flight measurements
We address the task of evaluating the basic performances of neutron time-of-flight spectrometers, by means of an appropriate figure of merit. Calculations of neutron flux, energy resolution, and figure of merit are presented with a critical discussion on their definitions. The results of Monte Carlo simulations for two presently operating facilities, CERN n_TOF and GELINA, are commented and compared
Nebrasca a Monte Carlo: code for simulation of neutron sources from deuteron photodisintegration
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