Derek Storm

Energy dependence of quasifree scattering in the 2H(p, pn)p reaction

Abstract We have measured the cross section for the reaction 2 H(p, pn) 1 H at 14, 17, 20 and 23 MeV incident energies. The proton and neutron counter angles were chosen to emphasize the quasifree p-n scattering process. The neutron counter efficiency was measured in order to obtain the absolute differential cross sections. The experimental results agree well with a modified simple impulse approximation, which is discussed.

Weak interaction studies with 6He

The 6He nucleus is an ideal candidate to study the weak interaction. To this end we have built a high-intensity source of 6He delivering ∼1010 atoms/s to experiments. Taking full advantage of that available intensity we have performed a high-precision measurement of the 6He half-life that directly probes the axial part of the nuclear Hamiltonian. Currently, we are preparing a measurement of the beta-neutrino angular correlation in 6He beta decay that will allow to search for new physics beyond the Standard Model in the form of tensor currents.

Absolute determination of the Na22(p,γ)Mg23 reaction rate in novae

Gamma-ray telescopes in orbit around the earth are searching for evidence of the elusive radionuclide 22Na produced in novae. Previously published uncertainties in the dominant destructive reaction, 22Na(p,γ)23Mg, indicated new measurements in the proton energy range of 150 to 300 keV were needed to constrain predictions. We have measured the resonance strengths, energies, and branches directly and absolutely by using protons from the University of Washington accelerator with a specially designed beam line, which included beam rastering and cold vacuum protection of the 22Na implanted targets. The targets, fabricated at TRIUMF-ISAC, displayed minimal degradation over a ∼20 C bombardment as a result of protective layers. We avoided the nneed to know the absolute stopping power, and hence the target composition, by extracting resonance strengths from excitation functions integrated over proton energy. Our measurements revealed that resonance strengths for Ep = 213, 288, 454, and 610 keV are stronger by factors of 2.4–3.2 than previously reported. Upper limits have been placed on proposed resonances at 198, 209, and 232 keV. These substantially reduce the uncertainty nin the reaction rate. We have re-evaluated the 22Na(p,γ) reaction rate, and our measurements indicate the resonance at 213 keV makes the most significant contribution to 22Na destruction in novae. Hydrodynamic nsimulations including our rate indicate that the expected abundance of 22Na ejecta from a classical nova is reduced by factors between 1.5 and 2, depending on the mass of the white-dwarf star hosting the nova explosion.

Charge-state distribution of Li ions from the β decay of laser-trapped He6 atoms

The accurate determination of atomic final states following nuclear β decay plays an important role in several experiments. In particular, the charge state distributions of ions following nuclear β decay are important for determinations of the β-ν angular correlation with improved precision. Beyond the hydrogenic cases, the decay of neutral He6 presents the simplest case. Our measurement aims at providing benchmarks to test theoretical calculations. The kinematics of Lin+ ions produced following the β decay of He6 within an electric field were measured using He6 atoms in the metastable (1s2s,S13) and (1s2p,P23) states confined by a magneto-optical trap. The electron shakeoff probabilities were deduced, including their dependence on ion energy. We find significant discrepancies on the fractions of Li ions in the different charge states with respect to a recent calculation.

Laser trapped 6He as a probe of the weak interaction and a test of the sudden approximation

Synopsis Correlations between β decay products are sensitive observables to look for exotic contributions to the weak interaction excluded by the Standard Model of particle physics. To precisely measure the β − ν angular correlation parameter, a βν , in 6 He β decay, the radioactive atoms are trapped in a magneto-optical trap and the momentum of β particles and 6 Li recoil ions are measured in coincidence. The shake-off process, leading to higher charge states of the Li, plays an important role in this observation and must be studied carefully. Its study provides stringent tests of the sudden approximation for atomic calculations in this few electron system.

Comparison of inclusive inelastic scattering of. pi. sup + and. pi. sup minus from nuclei at 100 MeV

Inclusive inelastic scattering spectra from C, Ca, Sn, and Pb were measured for 100-MeV pions at a number of angles. The observed ratios of the {pi}{sup {minus}} and {pi}{sup +} total inelastic cross sections for the different targets are explained in terms of a simple model which is based on the assumption that the scattered pion has interacted with only one nucleon. This model also accounts for the ratio between normal and charge-exchange scattering cross sections at 100 MeV.

Interplay Between Pion Absorption and Inclusive-Inelastic Scattering on Hydrogen and Helium Isotopes for 96.5-MeV Kinetic Energy Pions

Measurements of double-differential cross sections for inclusive-inelastic scattering of 96.5-MeV pions from hydrogen and helium isotopes are presented. Differential and angle-integrated cross sections are obtained. Distorted wave impulse approximation calculations are reported. The interplay between inclusive-inelastic scattering and pion absorption is discussed.