A. Galonsky

Energy Systematics of the Giant Gamow-Teller Resonance and a Charge-Exchange Dipole Spin-Flip Resonance

Energy systematics of the giant Gamow-Teller resonance and a charge-exchange resonance excited by a L = 1, S = 1 interaction are presented. Plots of the energy separation between each resonance and the IAS versus (N − Z)A can be represented approximately by linear functions.

Coulomb dissociation of 11Li.

Kinematically complete measurements for Coulomb dissociation of [sup 11]Li into [sup 9]Li+2[ital n] were made at 28 MeV/nucleon. The [ital n]-[ital n] correlation function suggests a large source size for the two-neutron emission. The electromagnetic excitation spectrum of [sup 11]Li has a peak, as anticipated in low-energy dipole resonance models, but a large post-breakup Coulomb acceleration of the [sup 9]Li fragment is observed, indicating a very short lifetime of the excited state and favoring direct breakup as the dissociation mechanism.

Systematics of the excitation of M1 resonances in medium heavy nuclei by 200 MeV proton inelastic scattering

Abstract In a series of seventeen nuclei ranging from 51 V to 14 Ce, broad resonance structures are observed at energies between 8 and 10 MeV, nearly mass independent. These resonances have very forward peaked angular distributions which imply that they are populated by an angular momentum transfer of zero. This together with the observed excitation energies suggests an M1 character for these resonances. In 51 V, 58 Ni, 60 Ni, 62 Ni, a sharp peak located at an excitation energy above the threshold for neutron emission is interpreted as a part of the T 0 + 1 component of the M1 resonance. Cross sections are given for all the M1 resonances. For 58 Ni, 90 Zr, 92 Mo, 120 Sn and 140 Ce, an “attenuation” factor for the cross sections is extracted in a DWIA calculation assuming simple shell-model structures for these resonances.

An energy-dependent Lane-model nucleon-nucleus optical potential☆

An energy-dependent Lane-model nucleon-nucleus optical potential is presented. The isovector strength parameters of the potential have been determined by fitting (p, n) IAS angular-distribution data between 25 and 45 MeV for targets from 48Ca to 208Pb. The isoscalar strength parameters have been obtained by requiring that the Lane-model potential reproduce the Becchetti-Greenlees Coulomb-corrected proton potential. The energy associated with the proton in all energy-dependent parts of the potential is reduced by the average Coulomb potential inside the nucleus. The main result of the parameter search, other than determining the strength of the isovector energy dependence, is to redistribute the isovector strength found by Becchetti and Greenlees between the real-volume and imaginary-surface terms. The Lane-model optical potential so obtained is reasonably successful in reproducing (p, p), (p, n) IAS, and (n, n) scattering over a wide mass and energy range.

Particle identification via pulse-shape discrimination with a charge-integrating ADC

Abstract A charge-integrating ADC has been used to sample the intensity in two different time regions of a pulse and thus to sense the shape of the pulse. This idea has been applied to produce neutron/γ-ray discrimination from pulses in a liquid scintillation detector. Optimization of available parameters yields good pulse-shape discrimination for pulses greater than those produced by 100 keV electrons. The method uses only general purpose electronics.

On the nature of low-lying collective 1+ states in the heavy deformed nuclei 154Sm, 156Gd and 164Dy and in the f72 shell nucleus 46Ti

Abstract High resolution inelastic proton scattering at 201 MeV on 154Sm, 156Gd and 164Dy is used to clarify the nature of low-lying magnetic dipole states previously observed in inelastic electron scattering. An upper limit on the spin contribution to these collective magnetic dipole excitations is presented. The roles of spin and convection currents are also studied by inelastic proton and electron scattering to the low-lying 1+ state at 4.319 MeV in the f 7 2 - shell nucleus 46Ti. A substantial orbital contribution is observed in all cases.

Evidence for an l=0 ground state in 9He

Abstract The unbound nuclear systems 10 Li and 9 He were produced in direct reactions of 28 MeV/u 11 Be incident on a 9 Be target. The distributions of the observed velocity differences between the neutron and the charged fragment show a strong influence of final-state interactions. Since the neutron originates in a dominant l =0 initial state, a selection-rule argument allows a firm l =0 assignment for the lowest odd-neutron state in 10 Li. We report the results suggesting a very similar unbound state in 9 He, characterized by an s-wave scattering length more negative than −10 fm corresponding to an energy of the virtual state of less than 0.2 MeV. Shell-model calculations cast light on the reasons for the disappearance of the magic shell gap near the drip line.

The initial organic products of fixation of 13N-labeled nitrogen gas by the blue-green alga Anabaena cylindrica

Methods have been developed for the rapid isolation and characterization of the first organic products of fixation of 13N-labeled N2. In experiments with the blue-green alga, Anabaena cylindrica, glutamine is the first 13N-labeled organic product observed, and glutamate is the second. The results indicate that the glutamine synthetase/glutamate synthase pathway is operative in this blue-green alga.

Response functions of organic scintillators to high energy neutrons

Abstract Two cylindrical liquid scintillators of dimensions 5 cm × 5 cm and 12.5 cm × 12.5 cm, filled with NE213, were calibrated with high energy neutrons from E n = 3 MeV to E n = 75 MeV at the time-of-flight facility associated with the Michigan State University Cyclotron. Pulse shape discrimination was used on each detector to separate the protons and alphas produced by neutron interactions from the electrons produced by gamma rays. Response functions for monoenergetic neutrons from about 2 MeV to 75 MeV have been determined. These response functions are very different from the calculated response using the Monte Carlo method. The implications of these calibrations for measurements on high energy neutrons using liquid scintillators are discussed.

A large-area, position-sensitive neutron detector with neutron/γ-ray discrimination capabilities

Abstract To further study neutron-rich halo nuclei, we have constructed a neutron detector array. The array consists of two separate banks of detectors, each of area 2 × 2m 2 and containing 250l of liquid scintillator. Each bank is position-sensitive to better than 10 cm. For neutron time-of-flight measurements, the time resolution of the detector has been demonstrated to be about 1 ns. By using the scintillator NE-213, we are able to distinguish between neutron and γ-ray signals above 1 MeV electron equivalent energy. Although the detector array was constructed for a particular experiment it has also been used in a number of other experiments.