J.R. Shepard

The effect of pickup-stripping contributions on the selection of a unique 3He optical potential☆

Abstract The coupling of pickup-stripping channels in 3 He elastic scattering has been shown to have a large effect on the elastic cross section at back angles for higher projectile energies. Quantitative treatment of these effects leads to the conclusion that the “deep” family of mass-3 optical potentials is selected by fitting to high energy, back angle elastic scattering data. This is in contrast to recent optical model studies which have concluded that such data can be fit only by using a “shallow” potential. Consistency is now found between those mass-3 potential families required in certain reaction studies and those indicated for elastic scattering.

Exact finite range DWBA results for the 12C(p, d)11C reaction at 700 MeV

The differential cross-sections for the 12C(p, d)11C (g.s.) reaction at 700 MeV have been calculated in a full finite range DWBA approach. The absolute cross sections agree with the data and are dominated by contributions arising from the deuteron D-state.

Observation of Fermi and Gamow-Teller strength in the 800 MeV(p, n) reaction

Abstract Angular distributions have been measured for the (p, n) reaction on targets of Li, C, C, and N at 800 MeV with an energy resolution of 2.7 MeV allowing observation of discrete nuclear levels. As is the case at lower energies, this reaction is very selective, emphasizing Gamow-Teller (GT) and Fermi transitions. Absolute cross sections of pure GT transitions are reproduced by impulse approximation calculations. The ratio |Jστ|2/|Jτ|2 was extracted from C and N measurements at 800 MeV and from a C measurement at 31

New 0+ states in 50Cr observed via the (p, t) reaction

Abstract Measurements of differential cross sections in the 52Cr(p, t) reaction at 27 MeV provide identification of four previously unreported 0+ states in the 3.8–4.8 MeV excitation region of the stable nucleus 50Cr. Additional spin-parity information is provided through observation of L = 2, 3 and 4 transitions.

Analyzing power measurements for the 13C(p,d)12C reaction at 200 and 400 MeV

Abstract Cross sections and analyzing powers for the 13C( p ,d) reaction have been measured at 200 and 400 MeV to the 0+, ground state and 2+, 4.44 MeV state of 12C. While the cross sections are rather structureless, DWBA calculations in exact finite range account well for both the magnitude and shape of the angular distributions. On the other hand, the measured analyzing powers are in serious disagreement with the DWBA calculations.

Meson exchange current corrections to magnetic moments in quantum hadro-dynamics

Abstract We have calculated pion exchange current corrections to the magnetic moments of closed shell ±1 particle nuclei near A=16 and 40 within the framework of quantum hadro-dynamics (QHD). We find that the correction is significant and that, in general, the agreement of the QHD isovector moments with experiment is worsened. Comparisons to previous non-relativistic calculations are also made.

Complex form factors in nucleon transfer reactions

Abstract The effect of an imaginary component in the form factor for (p, d) and (p, t) reactions has been examined. Following a recently developed procedure, several inadequacies of the DWBA description of these reactions, particularly those involving L = 0 transfers, are largely overcome.

P-Ay for excitation of natural and unnatural-parity states of 12C by 400 MeV protons

Abstract Differences of the polarization ( P ) and analyzing power ( A y ) have been measured between 5° and 14° for the lowest isoscalar 1 + and isovector 1 + and 2 + states in 12 C excited by 400 MeV protons. This is the first measurement of P - A y in an energy regime where the impulse approximation is most valid. Values of P - A y for all states are compared to both nonrelativistic and relativistic model calculations, which only qualitatively describe the data.

A study of the reaction 16O(p, p')16O exciting the 6.05 MeV O+ level

Abstract The cross section for excitation of the 6.05 MeV state in 16 O is measured. A parameter-free microscopic calculation gives good agreement with the data.

A study of the 12N 2.43 MeV level

Abstract We have measured the differential cross sections for the reactions 12 C( τ , τ ′) 12 C(17.77 MeV 0 + T =1) and 12 C( τ , t) 12 N(2.43 MeV) at E τ =44 MeV. The similar shapes of the angular distributions and the relative magnitudes of the cross sections suggest that the 12 N 2.43 MeV level is the 0 + T =1 analog to the q12 C 17.77 MeV level. We have also studied the reaction 14 N(p,t) 12 N(2.43 MeV) at E p =52 MeV. The strength with which this level is excited in this reaction is consistent with reasonable two-step calculations assuming the 2.43 MeV level to have J π =0 + .