C. H. Johnson

Nuclear structure of 49Ca above 5 MeV excitation from n + 48Ca and astrophysics for 30keV neutrons

Abstract The level structure of 49 Ca has been investigated above the neutron separation energy by measurements of the total and capture cross sections for neutron energies up to 2 MeV. Transmission data were obtained for two 48 CaCO 3 samples enriched to 96% in 48 Ca and were analyzed in the R -matrix formalism for neutron energies up to 2 MeV. An upper limit of 0.07 × 10 −4 was placed upon the s-wave strength function (〈 Γ n o 〉/ D ) and an optical model real potential was deduced from the low energy total cross section. Approximately 45% of the 2 d 5 2 single particle strength is observed in the region below 2 MeV neutron energy. Model configurations based on continuum shell model calculations which describe this strength and its distribution are presented. Combined low energy results are used to obtain the maxwellian averaged capture cross section and the result is discussed in relation to the nucleosynthesis of 49 Ca and the anomalous abundances observed in an inclusion of the Allende meteorite.

Optical model scattering functions for low energy neutrons on 86Kr

Optical scattering functions are deduced from an R‐matrix analysis and subsequent averaging of high resolution 86Kr+n transmission data. These functions have been fitted by adjusting the well depths in an optical model with r0=rD=1.21 fm, a0=0.66 fm and aD=0.48 fm. The well depths are V0=51.5 MeV and Vso=5.5 MeV for l=1 and V0=48.5 for l=0. WD is about 3.5 MeV for s1/2, p1/2 and p3/2. Each well depth has an uncertainty of about ±1 MeV.

d5/2‐single particle strength in 48Ca+n

The neutron total cross section of /sup 48/Ca was measured up to 4 MeV and the data analyzed using an R-matrix code to obtain resonance parameters and potential scattering phase shifts. No s-wave resonances were observed and the small cross section (approx.0.5 b) at low energy requires a real well depth of 48 MeV. Three strong d-wave resonances (amounting to 45% of the single particle limit) were found in the 0.8 to 2.0 MeV energy region. Shell-model-in-the-continuum calculations agree with these observations.

s- and p-wave neutrons on /sup 30/Si and /sup 34/S: Spherical optical model analysis

The s- and p-wave neutron scattering functions obtained previously by R-matrix analyses of high resolution transmission data for 0--1.4 MeV neutrons on /sup 30/Si and /sup 34/S have been averaged by means of a simple analytic approximation to obtain experimental optical model scattering functions. To describe these with a spherical optical model potential requires the real well depth to be about 20% deeper for p waves than for s waves. This result agrees with an earlier analysis for /sup 32/S and suggests that deformation effects must be included for all three nuclei.