A. L. Cole

Measurement of the Gamow-Teller strength distribution in Co-58 via the Ni-58(t,He-3) reaction at 115 MeV/nucleon

Electron capture and beta decay play important roles in the evolution of presupernovae stars and their eventual core collapse. These rates are normally predicted through shell-model calculations. Experimentally determined strength distributions from charge-exchange reactions are needed to test modern shell-model calculations. We report on the measurement of the Gamow-Teller strength distribution in Co-58 from the Ni-58(t,He-3) reaction with a secondary triton beam of an intensity of similar to 10(6) pps at 115 MeV/nucleon and a resolution of similar to 250 keV. Previous measurements with the Ni-58(n,p) and the Ni-58(d,He-2) reactions were inconsistent with each other. Our results support the latter. We also compare the results to predictions of large-scale shell-model calculations using the KB3G and GXPF1 interactions and investigate the impact of differences between the various experiments and theories in terms of the weak rates in the stellar environment. Finally, the systematic uncertainties in the normalization of the strength distribution extracted from Ni-58(He-3, t) are described and turn out to be nonnegligible due to large interferences between the Delta L=0,Delta S=1 Gamow-Teller amplitude and the Delta L=2,Delta S=1 amplitude.

New experimental efforts along the rp-process path

The level structure just above the proton threshold of the nucleus 30S has been studied using the neutron removal process on fast radioactive beams at the National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University. In this work we provide a description of the experimental setup. The present status of the analysis is also discussed.

Nucleosynthesis of proton-rich nuclei. Experimental results on the rp-process

We report in this study the nuclear properties of proton-rich isotopes located along the rp-process path. The experiments have recently been performed at the National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University. The level properties above the proton separation energy of the nuclei 30S, 36K and 37Ca were measured with precision of < 10 keV. This will allow a reduction in the determination of the astrophysical (p,γ) reaction rate under rp-process conditions.

Gamow-Teller strengths in 24 Na using the 24 Mg( t , 3 He) reaction at 115 A MeV

Gamow-Teller transitions from 24 Mg to 24 Na were studied via the (t, 3 He) reaction at 115A MeV using a secondary triton beam produced via fast fragmentation of 150A MeV 16 O ions. Compared to previous (t, 3 He) experiments at this energy that employed a primary a beam, the secondary beam intensity is improved by about a factor of five. Despite the large emittance of the secondary beam, an excitation-energy resolution of ∼200 keV is achieved. A good correspondence is found between the extracted Gamow-Teller strength distribution and those available from other charge-exchange probes. Theoretical calculations using the newly developed USDA and USDB sd-shell model interactions reproduce the data well.

Gamow-Teller strengths inNa24using the24Mg(t,3He)reaction at115AMeV

Gamow-Teller transitions from 24 Mg to 24 Na were studied via the (t, 3 He) reaction at 115A MeV using a secondary triton beam produced via fast fragmentation of 150A MeV 16 O ions. Compared to previous (t, 3 He) experiments at this energy that employed a primary a beam, the secondary beam intensity is improved by about a factor of five. Despite the large emittance of the secondary beam, an excitation-energy resolution of ∼200 keV is achieved. A good correspondence is found between the extracted Gamow-Teller strength distribution and those available from other charge-exchange probes. Theoretical calculations using the newly developed USDA and USDB sd-shell model interactions reproduce the data well.