K. Amos

Alternative evaluations of halos in nuclei

Data for the scattering of {sup 6}He, {sup 8}He, {sup 9}Li, and {sup 11}Li from hydrogen are analyzed within a fully microscopic folding model of proton-nucleus scattering. Current data suggest that of these only {sup 11}Li has a noticeable halo. For {sup 6}He, we have also analyzed the complementary reaction {sup 6}Li({gamma},{pi}{sup +}){sup 6}He{sub g.s.}. The available data for that reaction support the hypothesis that {sup 6}He may not be a halo nucleus. However, those data are scarce and there is clearly a need for more to elicit the microscopic structure of {sup 6}He. (c) 2000 The American Physical Society.

Analyzing power in elastic scattering of 6He from a polarized proton target at 71 MeV/nucleon

The vector analyzing power has been measured for the elastic scattering of neutron-rich {sup 6}He from polarized protons at 71 MeV/nucleon making use of a newly constructed solid polarized proton target operated in a low magnetic field and at high temperature. Two approaches based on local one-body potentials were applied to investigate the spin-orbit interaction between a proton and a {sup 6}He nucleus. An optical model analysis revealed that the spin-orbit potential for {sup 6}He is characterized by a shallow and long-ranged shape compared with the global systematics of stable nuclei. A semimicroscopic analysis with an {alpha}+n+n cluster folding model suggests that the interaction between a proton and the {alpha} core is essentially important in describing the p+{sup 6}He elastic scattering. The data are also compared with fully microscopic analyses using nonlocal optical potentials based on nucleon-nucleon g matrices.

An algebraic solution of the multichannel problem applied to low energy nucleon-nucleus scattering

This is a pre-print version published in Nuclear Physics A

Analyzing power for proton elastic scattering from the neutron-rich He6 nucleus

Vector analyzing power for the proton-{sup 6}He elastic scattering at 71 MeV/nucleon has been measured for the first time, with a newly developed polarized proton solid target, which works at a low magnetic field of 0.09 T. The results are found to be incompatible with a t-matrix folding model prediction. Comparisons of the data with g-matrix folding analyses clearly show that the vector analyzing power is sensitive to the nuclear structure model used in the reaction analysis. The {alpha}-core distribution in {sup 6}He is suggested to be a possible key for understanding the nuclear structure sensitivity.

Predicting Narrow States in the Spectrum of a Nucleus beyond the Proton Drip Line

Properties of particle-unstable nuclei lying beyond the proton drip line can be ascertained by considering the (usually known) properties of its mirror neutron-rich system. We have used a multichannel algebraic scattering theory to map the known properties of the neutron-14C system to those of the proton-14O one from which we deduce that the particle-unstable 15F will have a spectrum of two low-lying broad resonances of positive parity and, at higher excitation, three narrow negative-parity ones. A key feature is to use coupling to Pauli-hindered states in the target.

Role of the Pauli principle in collective-model coupled-channel calculations.

A multichannel algebraic scattering theory, to find solutions of coupled-channel scattering problems with interactions determined by collective models, has been structured to ensure that the Pauli principle is not violated. By tracking the results in the zero coupling limit, a correct interpretation of the subthreshold and resonant spectra of the compound system can be made. As an example, the neutron-12C system is studied defining properties of 13C to 10 MeV excitation. Accounting for the Pauli principle in collective coupled-channels models is crucial to the outcome.

24.5 A MeV 6He+p elastic and inelastic scattering

The structure of 6 He is explored with proton elastic and inelastic scattering to the first 2 + excited state (Q =− 1. 8M eV) of 6 He in the inverse kinematics using a 24.5 A MeV 6 He beam. The distorted wave approximation (DWA) with an optical potential obtained by folding an effective nucleon–nucleon (NN) g-matrix with the 6 He density matrix elements as given by a large basis shell model is used to analyse the data. The comparison of predictions with the data confirms the view that 6 He has

A method for calculating the Jost function for analytic potentials

SummaryA combination of the variable-constant and complex coordinate rotation methods is used to solve the two-body Schrödinger equation. The latter is replaced by a system of linear first-order differential equations, which enables one to perform direct calculation of the Jost function for all complex momenta of physical interest, including the spectral points corresponding to bound and resonance states. Explicit forms of the equations, appropriate for central short-range and Coulombtailed potentials, are given. Within the proposed method, the scattering, bound, virtual, and resonance state problems can be treated in a unified way. The effectiveness of the method is demonstrated by a numerical example.

Microscopic and macroscopic aspects of 135 MeV proton scattering from 16O

Abstract Differential cross sections have been measured for the scattering of 135 MeV protons from 16 O and data from the transitions to 13 states (up to 19.5 MeV excitation) have been analysed using microscopic and macroscopic nuclear reaction models. Extensive collective model calculations have been made of the transitions to all natural-parity states. The deformation parameters for the 4p4h rotational band are in good agreement with theoretical models. The inelastic scattering data from the excitation of the negative-parity states have also been analysed in the distorted-wave approximation using microscopic (shell and RPA) models of nuclear structure and with density-dependent two-nucleon t -matrices. For positive-parity states, we report the first shell-model calculation using the complete 2ħω basis space and find that the triplet of 2p2h states (4 + , 2 + , 0 + ) around 11 MeV excitation is quite well described by this model, as may be a 1 + state which is observed for the first time by proton scattering from 16 O.

Density-dependent forces and large-basis structure models in the analyses of 12C(p, p') reactions at 135 MeV

Abstract Differential cross sections have been measured for the elastic and inelastic scattering of 135 MeV protons from 12C. The data from the transitions to 9 selected states up to 18.3 MeV in excitation have been analysed using a distorted wave approximation with various microscopic model nuclear structure transition densities and free and density-dependent two-nucleon t-matrices. Clear signatures of the density dependence of the t-matrix are defined and the utility of selected transitions to test different attributes of that t-matrix when good nuclear structure models are used is established.