W. E. Ormand

Neutrino capture cross sections for 40Ar and β-decay of 40Ti

Abstract Shell-model calculations of solar neutrino absorption cross sections for 40Ar, the proposed component of the ICARUS detector, are presented. It is found that low-lying Gamow-Teller transitions lead to a significant enhancement of the absorption rate over that expected from the Fermi transition between the isobaric analog states, leading to an overall absorption cross section for 8B neutrinos of (11.5 ± 0.7) × 10−43 cm2 or a total expected rate of 6.7 ± 2.5 SNU. We also note that the pertinent Gamow-Teller transitions in 40Ar are experimentally accessible from the β-decay of the mirror nucleus 40Ti. Predictions for the branching ratios to states in 40Sc are presented, and the theoretical halflife of 55 ± 5 ms is found to be in good agreement with the experimental value of 56−12+18 ms.

Demonstration of the auxiliary-field Monte Carlo approach for sd-shell nuclei

We apply the auxiliary-field Monte Carlo approach to the nuclear shell model in the 1s-0d configuration space. The Hamiltonian was chosen to have isovector pairing and isoscalar multipole-multipole interactions, and the calculations were performed within the fixed-particle, canonical ensemble. The results demonstrate the feasibility of the method for N≠Z even-even and odd-odd N=Z nuclei. In particular, static observables for even-even Ne isotopes and 22Na compare well with results obtained from exact diagonalization of the Hamiltonian. Response functions are presented for 22Ne and compared with exact results, and the viability of cranked calculations for N≠Z even-even nuclei is addressed. We present methods for computing observables in the canonical ensemble using Fourier extraction, and for determining the nucelar shape.

Shell model Monte Carlo calculations for 170Dy

Abstract We present the first auxiliary field Monte Carlo calculations for a rare earth nucleus, 170 Dy. We calculate various static Hamiltonian is used to demonstrate the physical properties that can be studied in this region. We calculate various static observables for both uncranked and crancked systems and show how the shape distribution evolves with temperature. We also introduce a discretization of the path integral that allows a more efficient Monte Carlo sampling.

The solar neutrino capture cross section for 23Na

Abstract A coincidence (electron, γ-ray) experiment designed to identify one or more components of the solar neutrino spectrum has been proposed based on a large array of NaBr detectors. In support of the design of this detector, we calculate the solar neutrino absorption rate for v + 23 Na → 23 Mg + e − within the Standard Solar Model making use of both experimental and theoretical data for the structure of the two nuclei involved. It is found that the inclusion of excited states in 23Mg enhances the absorption cross section by ≈30%, with approximately one third of this enhancement coming from excited states for which experimental data does not exist. The solar neutrino absorption rate is calculated to be 3.5 ± 1.3 SNU, which amounts to about one count every six days for the proposed detector.