77 research outputs found
Study of nuclear correlation effects via 12C(p,n)12N(g.s.,1+) at 296 MeV
We report measurements of the cross section and a complete set of
polarization observables for the Gamow--Teller reaction at a bombarding
energy of 296 MeV.
The data are compared with distorted wave impulse approximation calculations
employing transition form factors normalized to reproduce the observed
beta-decay value.
The cross section is significantly under-predicted by the calculations at
momentum transfers 0.5 .
The discrepancy is partly resolved by considering the non-locality of the
nuclear mean field. However, the calculations still under-predict the cross
section at large momentum transfers of 1.6 .
We also performed calculations employing random phase approximation response
functions and found that the observed enhancement can be attributed in part to
pionic correlations in nuclei.Comment: 5 figures, submitted to Phys. Lett.
Complete set of polarization transfer coefficients for the reaction at 346 MeV and 0 degrees
We report measurements of the cross-section and a complete set of
polarization transfer coefficients for the reaction at a
bombarding energy = 346 MeV and a reaction angle =
.
The data are compared with the corresponding free nucleon-nucleon values on
the basis of the predominance of quasi-elastic scattering processes.
Significant discrepancies have been observed in the polarization transfer
, which are presumably the result of the three-proton =
3/2 resonance.
The spin--parity of the resonance is estimated to be , and the
distribution is consistent with previous results obtained for the same reaction
at = 48.8 MeV.Comment: 4 figures, Accepted for publication in Physical Review
Spectroscopy of 24Al and extraction of Gamow-Teller strengths with the 24Mg(3He,t) reaction at 420 MeV
The 24Mg(3He,t)24Al reaction has been studied at E(3He)=420 MeV. An energy
resolution of 35 keV was achieved. Gamow-Teller strengths to discrete levels in
24Al are extracted by using a recently developed empirical relationship for the
proportionality between Gamow-Teller strengths and differential cross sections
at zero momentum transfer. Except for small discrepancies for a few weak
excitations, good agreement with previous 24Mg(p,n) data and nuclear-structure
calculations using the USDA/B interactions in the sd shell-model space is
found. The excitation energy of several levels in 24Al of significance for
determination of the 23Mg(p,gamma)24Al thermonuclear reaction rate were
measured. Results are consistent with two of the three previous (3He,t)
measurements, performed at much lower beam energies. However, a new state at
Ex(24Al)=2.605(10) MeV was found and is the third state above the proton
separation energy.Comment: 6 pages, 4 figure
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.
Isovector effective NN interaction in 28Si(p,n)28P(6-) at 198 MeV
We report measurements of the cross section and a complete set of polarization observables for the View the MathML source reaction at a bombarding energy of 198 MeV. The data are compared with distorted wave impulse approximation calculations employing response functions normalized to inelastic electron scattering. The spin-longitudinal polarized cross section IDq is slightly over-predicted by the calculations, while the normal spin-transverse polarized cross section IDn is significantly under-predicted. The calculated in-plane spin-transverse IDp and spin-scalar ID0 polarized cross sections agree well with the experimental data. These results are consistent with those for View the MathML source scattering at the same energy, and thus it is concluded that isospin-mixing effects are not responsible for the discrepancy between theory and experiment in the View the MathML source case. Energy half-off-shell effects as medium effects on the effective nucleon?nucleon interaction are also investigated and found to be too small to be responsible for the discrepancy
Pygmy dipole resonance in 208Pb
Scattering of protons of several hundred MeV is a promising new spectroscopic
tool for the study of electric dipole strength in nuclei. A case study of 208Pb
shows that at very forward angles J^pi = 1- states are strongly populated via
Coulomb excitation. A separation from nuclear excitation of other modes is
achieved by a multipole decomposition analysis of the experimental cross
sections based on theoretical angular distributions calculated within the
quasiparticle-phonon model. The B(E1) transition strength distribution is
extracted for excitation energies up to 9 MeV, i.e., in the region of the
so-called pygmy dipole resonance (PDR). The Coulomb-nuclear interference shows
sensitivity to the underlying structure of the E1 transitions, which allows for
the first time an experimental extraction of the electromagnetic transition
strength and the energy centroid of the PDR.Comment: submitted to Phys. Rev.
Complete electric dipole response and the neutron skin in 208Pb
A benchmark experiment on 208Pb shows that polarized proton inelastic
scattering at very forward angles including 0{\deg} is a powerful tool for
high-resolution studies of electric dipole (E1) and spin magnetic dipole (M1)
modes in nuclei over a broad excitation energy range to test up-to-date nuclear
models. The extracted E1 polarizability leads to a neutron skin thickness
r_skin = 0.156+0.025-0.021 fm in 208Pb derived within a mean-field model [Phys.
Rev. C 81, 051303 (2010)], thereby constraining the symmetry energy and its
density dependence, relevant to the description of neutron stars.Comment: 5 pages, 5 figures, revised mansucrip
Isospin symmetry of T_z =±3/2 →±1/2 Gamow-Teller transitions in A=41 nucllei
Under the assumption that isospin I is a good quantum number, isobaric analog states and various analogous transitions are expected in isobars with mass number A. The strengths of T_z=+3/2→+1/2 analogous Gamow-Teller (GT) transitions and analogous M1 transitions within the A=41 isobar quartet are compared in detail. The T_z= +3/2+1/2 GT transitions from the J^π=3/2+ ground state of ^K leading to excited J^π = 1/2^+, 3/2^+, and 5/2^+ states in ^Ca were measured using the (^3He,t) charge-exchange reaction. With a high energy resolution of 35 keV, many fragmented states were observed, and the GT strength distribution was determined up to 10 MeV excitation energy (E_x). The main part of the strength was concentrated in the E_x =4-6 MeV region. A shell-model calculation could reproduce the concentration, but not so well details of the strength distribution. The obtained distribution was further compared with two results of ^Ti βdecay studying the analogous T^z=-3/2→-1/2 GT strengths. They reported contradicting distributions. One-to-one correspondences of analogous transitions and analog states were assigned up to E_x=6 MeV in the comparison with one of these ^Ti β-decay results. Combining the spectroscopic information of the analog states in ^Ca and ^ Sc, the most probable J^π values were deduced for each pair of analog states. It was found that 5/2^+ states carry the main part of the observed GT strength, while much less GT strength was carried by 1/2^+ and 3/2^+ states. The gross features of the GT strength distributions for each J were similar for the isospin analogous T_z=±3/ 2→±1/2 transitions, but the details were somewhat different. From the difference of the distributions, isospin-asymmetry matrix elements of ≈8 keV were deduced. The Coulomb displacement energy, which is sensitive to the configuration of states, showed a sudden increase of about 50 keV at the excitation energy of 3.8 MeV. The strengths of several Ml transitions to the IAS in ^Ca were compared with the strengths of analogous GT transitions. It was found that ratios of the M1 and GT transition strengths were similar, suggesting that the contributions of the lτ term in M1 transitions are small
On the extraction of weak transition strengths via the (3He,t) reaction at 420 MeV
Differential cross sections for transitions of known weak strength were
measured with the (3He,t) reaction at 420 MeV on targets of 12C, 13C, 18O,
26Mg, 58Ni, 60Ni, 90Zr, 118Sn, 120Sn and 208Pb. Using this data, it is shown
the proportionalities between strengths and cross sections for this probe
follow simple trends as a function of mass number. These trends can be used to
confidently determine Gamow-Teller strength distributions in nuclei for which
the proportionality cannot be calibrated via beta-decay strengths. Although
theoretical calculations in distorted-wave Born approximation overestimate the
data, they allow one to understand the main experimental features and to
predict deviations from the simple trends observed in some of the transitions.Comment: 4 pages, 2 figure
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