21 research outputs found
Correlations of projectile like fragments in heavy ion reactions at Fermi energy
Correlations between pairs of projectile-like fragments, emitted by the
system at the laboratory bombarding energy of 515 MeV,
have been studied under two stipulated conditions: (1) at least one member of
the pair is emitted at an angle less than the grazing angle for the system, (2)
both the members of the pair are emitted at angles larger than the grazing
angle. A surprisingly large difference, by more than an order of magnitude, is
found between the correlations for the two cases. This observation could be
explained on the basis of a simple semi-classical break up model. Further
analysis of the variation of the charge correlation function with the
difference in the nuclear charges of the correlated pair showed trends which
are consistent with an "inelastic break up process", in which the projectile
breaks up at the radius of contact, in such a way that, one fragment
(preferably the lighter) is emitted to one side within the grazing angle, while
the other orbits around the target nucleus for a while and emerges on the other
side, at a negative scattering angle, much like in a deep inelastic scattering.Comment: 19 pages, 12 figures accepted by Eurp. Physics Journal
Renormalization of the weak hadronic current in the nuclear medium
The renormalization of the weak charge-changing hadronic current as a
function of the reaction energy release is studied at the nucleonic level. We
have calculated the average quenching factors for each type of current (vector,
axial vector and induced pseudoscalar). The obtained quenching in the axial
vector part is, at zero momentum transfer, 19% for the sd shell and 23% in the
fp shell. We have extended the calculations also to heavier systems such as
Ni and Sn, where we obtain stronger quenchings, 44% and 59%,
respectively. Gamow--Teller type transitions are discussed, along with the
higher order matrix elements. The quenching factors are constant up to roughly
60 MeV momentum transfer. Therefore the use of energy-independent quenching
factors in beta decay is justified. We also found that going beyond the zeroth
and first order operators (in inverse nucleon mass) does not give any
substantial contribution. The extracted renormalization to the ratio
at q=100 MeV is -3.5%, -7.1$%, -28.6%, and +8.7% for mass 16, 40, 56, and 100,
respectively.Comment: 28 pages, 6 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.
Gamow-Teller Strengths for Neutrino Detectors
This research was sponsored by the National Science Foundation Grant NSF PHY-931478
The Indiana University Neutron Polarization Facility (INPOL)
This research was sponsored by the National Science Foundation Grant NSF PHY-931478
A Measurement of Gamow-Teller Strength for 176Yb -> 176Lu and the Efficiency of a Solar Neutrino Detector
We report a 0-degree 176Yb(p,n)176Lu measurement at IUCF where we used 120
and 160 MeV protons and the energy dependence method to determine GT matrix
elements relative to the Fermi matrix element which can be calculated model
independently. The data show that there is an isolated concentration of GT
strength in the low lying 1+ states making the proposed Low Energy Neutrino
Spectroscopy (LENS) detector (based on neutrino captures on 176Yb) sensitive to
7Be and pp neutrinos and a promising detector to resolve the solar neutrino
problem.Comment: 11 pages, LATEX, 4 eps figure
LENDA, a Low Energy Neutron Detector Array for experiments with radioactive beams in inverse kinematics
The Low Energy Neutron Detector Array (LENDA) is a neutron time-of-flight
(TOF) spectrometer developed at the National Superconducting Cyclotron Lab-
oratory (NSCL) for use in inverse kinematics experiments with rare isotope
beams. Its design has been motivated by the need to study the spin-isospin
response of unstable nuclei using (p, n) charge-exchange reactions at
intermediate energies (> 100 MeV/u). It can be used, however, for any reaction
study that involves emission of low energy neutrons (150 keV - 10 MeV). The
array consists of 24 plastic scintillator bars and is capable of registering
the recoiling neutron energy and angle with high detection efficiency. The
neutron energy is determined by the time-of-flight technique, while the
position of interaction is deduced using the timing and energy information from
the two photomultipliers of each bar. A simple test setup utilizing radioactive
sources has been used to characterize the array. Results of test measurements
are compared with simulations. A neutron energy threshold of < 150 keV, an
intrinsic time (position) resolution of \sim 400 ps (\sim 6 cm) and an
efficiency > 20 % for neutrons below 4 MeV have been obtained.Comment: Version accepted for publication in Nucl. Instr. Methods A. Revised
text, 2 new figures added (one in section 4 and one in section 7
Few-body resonances in light nuclei
We have localized several few-body resonances in light nuclei, using methods which can properly handle two- or three-body resonant states. Among other results, we predict the existence of a three-neutron resonance, small spin-orbit splittings between the low-lying states in He-5 and Li-5, the nonexistence of the soft dipole resonance in He-6, new 1+ states in Li-8 and B-8, and the presence of a nonlinear amplification phenomenon in the 0+_2 state of C-12
Fragment Emission in S+Au Collisions at Fermi Energy
Intermediate mass fragment emission from the interaction of sulphur with gold 32S+197Au at a beam energy of 1.01 GeV (31.5 MeV A) was measured at various angles with silicon ΔE–E telescopes. At the most forward angle ϑ = 17°, an additional ΔE detector, an ionisation chamber was used. The measurements were successfully compared with other data of similar systems. Angle integration of cross sections was performed within the generalised moving source model. The isotopic cross sections were compared to theoretical calculations within quantum molecular dynamic and statistical multi-fragmentation models
Intermediate mass fragment emission in 32S + 51V, 109Ag, and 238U collisions at E = 31.6 MeV A
Intermediate mass fragment emission for reactions of 32S + 51V, 109Ag, and 238U has been studied. Double differential cross sections were analysed in terms of the generalised moving source model yielding charge distributions. Isotope ratios show strong fragment mass dependencies. The data were successfully reproduced by the coalescence model as well as by statistical multifragmentation model calculations. Quantum molecular dynamics model calculations were not so successful