Nelson Jarmie

Nuclear glory scattering

Abstract A simple model in terms of surface waves for nuclear back-scattering analogous to the optical explanation of the meteorological glory is derived for spin-0 and spin - 1 2 particles from spin-0 targets. Numerous examples of α scattering from spinless nuclei in the energy range from 18 to 50 MeV and π+ scattering from protons in the range 2 to 8 GeV are fit successfully with the model. The model yields estimates of the radius of interaction whose values are in agreement with radii determined by other means. Other theories and models relating to backscattering are discussed and attention is called to the similarity between our model and the Regge-pole treatment of this problem by Ceuleneer, Demeur, and Reignier.

Low-Energy nuclear reactions with hydrogen isotopes

Abstract Using the Los Alamos Low-Energy Fusion Cross-Section Facility (LEFCS), we have completed the study of the D(t, α)n reaction from Et = 12.5–117 keV, and now have measured angular distributions of the reactions D(d, p)T and D(d, 3He)n from Ed= 20–117 keV. The experimental equipment features a windowless cryogenic target, a precision beam-intensity calorimeter, a 10 to 120 keV accelerator producing negative tritium ions, an accurate target gas-flow and temperature system, and a tritium gas-handling system. Most of the quite anisotropic angular distributions of the D+D reactions have relative errors of about 1% and the integrated cross-sections have absolute errors of about 1.5%. Astrophysical S functions extracted from the data and also from a least-squares fit of a+b cos2θ to the data show a curious behavior with energy. The cross-sections, which agree with previous but less accurate data, are compared with R-matrix calculations. We also show preliminary results for alpha-particle spectra of the T(t, α)nn reaction. A feature of this experiment is the flow through our windowless target of 1.5 standard liters of tritium gas per day.

Cross section of the capture reaction He3(α,γ)Be7

The cross sections for the astrophysically significant reactions /sup 3/He(..cap alpha..,..gamma..) /sup 7/Be and /sup 4/He(/sup 3/He, ..gamma..) /sup 7/Be have been measured near 900 keV in the center of mass by measuring the activity of /sup 7/Be produced in a gas cell. The results imply a zero-energy cross-section factor S(0) of 0.63(4) keV b, consistent with the larger of previous measurements. Extant values of S(0) are reviewed and a recommended value for use in stellar evolution calculations is presented.

Cross section of the capture reaction /sup 3/He(. cap alpha. ,. gamma. ) /sup 7/Be

The cross sections for the astrophysically significant reactions /sup 3/He(..cap alpha..,..gamma..) /sup 7/Be and /sup 4/He(/sup 3/He, ..gamma..) /sup 7/Be have been measured near 900 keV in the center of mass by measuring the activity of /sup 7/Be produced in a gas cell. The results imply a zero-energy cross-section factor S(0) of 0.63(4) keV b, consistent with the larger of previous measurements. Extant values of S(0) are reviewed and a recommended value for use in stellar evolution calculations is presented.

Thin metal windows for gas targets

Abstract Experience with thin metal foils as windows for hydrogen gas targets that are irradiated by particle beams, indicated that molybdenum is often the metal of choice. Where a high-Z material is needed for low-background neutron production, a new alloy of 75% Pt-25% Ir appears to be useful. Experience with Havar and tantalum foils is also reported.

The interactions of polarised tritons with 32S

Abstract Cross sections and analysing powers have been measured for the elastic and inelastic scattering of tritons from 32 S, along with the 32 S ( t , α) 31 P reaction data, using the 17 MeV polarised triton beam available at the Los Alamos National Laboratory. An optical model analysis of the elastic scattering data has yielded a triton spin-orbit potential with an unconventional geometry. The inelastic analysing powers have shown a requirement for including the deformation of the spin-orbit potential in the coupling potential form factor. The ( t , α ) reaction data have been analysed using the zero-range DWBA. Certain features of this reaction data which could not be described by the DWBA are well predicted when the analysis is extended to include explicitly the inelastic couplings and two-step processes through a CCBA calculation.

A surface-delta description of analyzing power measurements for collective states of Ni and Zn isotopes☆

Abstract Analyzing powers and differential cross sections for the inelastic scattering of 15 MeV polarized protons to the stronger collective states of 58, 60 Ni and 64 Zn have been measured. The data were compared to detailed microscopic reaction calculations using a central plus spin-dependent effective interaction. The nuclear structure wave functions used were obtained from a quasiparticle random-phase appoximation calculation using a spin-dependent surface delta interaction and a basis set containing both neutron and proton configurations. The overall quality of the fits strongly suggests that the surface-delta wave functions provide a good representation for spherical nuclei in this intermediate mass range. The effects of exchange and further modifications to the microscopic effective interaction are discussed.

Study of the reaction H(d, 2p)n at 16 MeV around collinear configurations

Abstract The cross section and the analyzing powers Ay, Axx, Axz and Ayy for the reaction H ( d , 2 p ) n are studied by kinematically overdetermined measurements at an incident energy of 16 MeV at collinear and somewhat off-collinear kinematic conditions. A three-body Faddeev model using two realistic separable potentials that have different short-range parts gives a good fit to the data. Uncertainties in Coulomb corrections make it difficult to draw definitive conclusions about possible three-nucleon force effects at collinearity conditions.

Hydrogen fusion-energy reactions

Abstract At the Los Alamos Ion Beam Facility we have installed a low-energy fusion cross section (LEFCS) apparatus specifically designed to measure cross sections to high accuracy for the various fusion-energy reactions among the hydrogen isotopes in the bombarding-energy range 10 to 120 keV. To date, we have completed and published our study of the D(t,α)n reaction, have finished data-taking for the D(d,p)T and D(d, 3He)n reactions, and have nearly finished data-taking for the T(t,α)nn reaction. Here we describe the LEFCS facility, present final and preliminary results for these reactions, and compare them with R-matrix calculations.

Thin Epitaxial Silicon for De/Dx Detectors

The techniques for fabricating thin self-supporting epitaxial films for dE/dx detectors have been studied. Detectors having thicknesses between 1 and 4 ¿m with areas of 12.5 mm2 have been fabricated and tested. The response of the detectors has been studied with alpha particles, oxygen ions, and fission fragments.