155 research outputs found
Performance of the neutron polarimeter NPOL3 for high resolution measurements
We describe the neutron polarimeter NPOL3 for the measurement of polarization
transfer observables with a typical high resolution of 300 keV
at 200 MeV.
The NPOL3 system consists of three planes of neutron detectors.
The first two planes for neutron polarization analysis are made of 20 sets of
one-dimensional position-sensitive plastic scintillation counters with a size
of 100 cm 10 cm 5 cm, and they cover the area of 100
100 .
The last plane for detecting doubly scattered neutrons or recoiled protons is
made of the two-dimensional position-sensitive liquid scintillation counter
with a size of 100 cm 100 cm 10 cm.
The effective analyzing powers and double scattering
efficiencies were measured by using the three kinds
of polarized neutrons from the , , and reactions at = 198 MeV.
The performance of NPOL3 defined as
are similar to that of the
Indiana Neutron POLarimeter (INPOL) by taking into account for the counter
configuration difference between these two neutron polarimeters.Comment: 28 pages, 18 figures, submitted to Nucl. Instrum. Methods Phys. Res.
Complete Set of Polarization Transfer Observables for the Reaction at 296 MeV and 0
A complete set of polarization transfer observables has been measured for the
reaction at and . The total spin transfer and the observable
deduced from the measured polarization transfer observables indicate that
the spin--dipole resonance at has greater
strength than strength, which is consistent with recent experimental and
theoretical studies. The results also indicate a predominance of the spin-flip
and unnatural-parity transition strength in the continuum. The exchange tensor
interaction at a large momentum transfer of is
discussed.Comment: 4 pages, 4 figure
Differential cross section for neutron-proton bremsstrahlung
The neutron-proton bremsstrahlung process is known to be
sensitive to meson exchange currents in the nucleon-nucleon interaction. The
triply differential cross section for this reaction has been measured for the
first time at the Los Alamos Neutron Science Center, using an intense, pulsed
beam of up to 700 MeV neutrons to bombard a liquid hydrogen target. Scattered
neutrons were observed at six angles between 12 and 32, and the
recoil protons were observed in coincidence at 12, 20, and
28 on the opposite side of the beam. Measurement of the neutron and
proton energies at known angles allows full kinematic reconstruction of each
event. The data are compared with predictions of two theoretical calculations,
based on relativistic soft-photon and non-relativistic potential models.Comment: 5 pages, 3 figure
Two-step contribution to the spin-longitudinal and spin-transverse cross sections of the quasielastic (p,n) reactions
The two-step contribution to the spin-longitudinal and the spin-transverse
cross sections of ^{12}C,^{40}Ca(p,n) reactions at 494 MeV and 346 MeV is
calculated. We use a plane-wave approximation and evaluate the relative
contributions from the one-step and the two-step processes. We found that the
ratios of the two-step to the one-step processes are larger in the
spin-transverse cross sections than in the spin-longitudinal ones. Combining
these results with the distorted-wave impulse approximation (DWIA) results we
obtained considerable two-step contributions to the spin-longitudinal and the
spin-transverse cross sections. The two-step processes are important in
accounting for the underestimation of the DWIA results for the
spin-longitudinal and the spin-transverse cross sections.Comment: LaTeX 11 pages, 10 figure
Gamow-Teller strength distributions for nuclei in pre-supernova stellar cores
Electron-capture and -decay of nuclei in the core of massive stars
play an important role in the stages leading to a type II supernova explosion.
Nuclei in the f-p shell are particularly important for these reactions in the
post Silicon-burning stage of a presupernova star. In this paper, we
characterise the energy distribution of the Gamow-Teller Giant Resonance (GTGR)
for mid-fp-shell nuclei in terms of a few shape parameters, using data obtained
from high energy, forward scattering (p,n) and (n,p) reactions. The energy of
the GTGR centroid is further generalised as function of nuclear
properties like mass number, isospin and other shell model properties of the
nucleus. Since a large fraction of the GT strength lies in the GTGR region, and
the GTGR is accessible for weak transitions taking place at energies relevant
to the cores of presupernova and collapsing stars, our results are relevant to
the study of important -capture and -decay rates of arbitrary,
neutron-rich, f-p shell nuclei in stellar cores. Using the observed GTGR and
Isobaric Analog States (IAS) energy systematics we compare the coupling
coefficients in the Bohr-Mottelson two particle interaction Hamiltonian for
different regions of the Isotope Table.Comment: Revtex, 28 pages +7 figures (PostScript Figures, uuencoded, filename:
Sutfigs.uu). If you have difficulty printing the figures, please contact
[email protected]. Accepted for publication in Phys. Rev. C, Nov 01,
199
On the Strength of Spin-Isospin Transitions in A=28 Nuclei
The relations between the strengths of spin-isospin transition operators
extracted from direct nuclear reactions, magnetic scattering of electrons and
processes of semi-leptonic weak interactions are discussed.Comment: LaTeX, 8 pages, 1Postscript with figur
Roper excitation in reactions
We calculate differential cross sections and the spin transfer coefficient
in the reaction for proton
bombarding energies from 1 to 10 GeV and invariant masses spanning
the region of the N(1440) Roper resonance. Two processes --
excitation in the -particle and Roper excitation in the proton -- are
included in an effective reaction model which was shown previously to reproduce
existing inclusive spectra. The present calculations demonstrate that these two
contributions can be clearly distinguished via , even under kinematic
conditions where cross sections alone exhibit no clear peak structure due to
the excitation of the Roper.Comment: 12 pages, 11 ps figures, Late
Energy Dependence of the Ratio of Isovector Effective Interaction Strengths |J_στ/J_τ| from 0° (p,n) Cross Sections
This work was supported by the National Science Foundation Grants NSF PHY 78-22774 A03, NSF PHY 81-14339, and by Indiana Universit
Activation Measurements of the 7-Li(p,n)7-Be Reaction from 60-480 MeV
This research was sponsored by the National Science Foundation Grant NSF PHY 87-1440
Solar Neutrino Detector GT Strength Distributions Via (p,n) Reactions
This work was supported by the National Science Foundation Grant NSF PHY 81-14339 and by Indiana Universit
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