E.G. Adelberger

Study of the β decays of 37Ca and 36Ca

Abstract The β-delayed proton and γ-ray emission of 37Ca and 36Ca was studied at the projectile fragment separator at GSI Darmstadt. In the 37Ca study, the β-delayed γ decay was observed for the first time, and the half-life was redetermined, under essentially background-free conditions, as 181.1 ± 1.0 ms. The surprisingly high Γ γ Γ p values found for proton-unbound states in 37K drastically reduce former discrepancies between the Gamow-Teller strength values B(GT) measured in the 37Ca β decay and those deduced from the 37Cl(p,n)37Ar mirror reaction. Our data provide evidence, on a level of 1.6 standard deviations, for isospin-mixing of the lowest T = 3 2 level in 37K. In the 36Ca study, a complete β decay scheme, including the β-delayed proton emission into the ground and first excited states of 35Ar as well as the β-delayed γ decay, was measured for the first time. The 36Ca half-life was remeasured with improved accuracy to be 102 ± 2 ms. Our data exclude a 1+ assignment for two near-thrd states in 36K that could be important resonances in 35Ar(p,γ) reactions of astrophysical interest. The B(GT) distributions in 37,36Ca decays are compared to results obtained from large-scale sd shell-model calculations.

40Ti β decay and the neutrino capture cross section of 40Ar

Abstract 40 Ti β decay was studied at GANIL using the LISE3 spectrometer. A decay scheme was deduced from twenty-one observed β-delayed proton transitions feeding the ground and first excited states of 39 Ca. The 40 Ti half-life was found to be 51.7(6) ms. These results imply that the ICARUS 40 Ar detector has an effective absorption cross section for 8 B solar neutrinos of 14.5(4) × 10 −43 cm 2 ; 73% of the total cross section arises from Gamow-Teller transitions that were neglected in early estimates of the ICARUS efficiency.

β-decay of37Ca

Abstract The β-decay of 37Ca has been studied. The half-life was remeasured with improved precision to be 181.1 ± 1.0 ms, and β-delayed γ-rays were observed for the first time. The surprisingly high Γ γ Γ p values for proton-unbound states in 37K drastically reduce former discrepancies between the Gamow-Teller strength values B(GT) measured in the 37Ca β-decay and those deduced from the 37Cl(p,n)37Ar mirror reaction.

Gamow-Teller strength in the β-decay of 36Ca

Abstract The β-decay of 36 Ca has been studied at the projectile fragment separator at GSI Darmstadt. The measured Gamow-Teller strength function B (GT), deduced from the observed β-delayed proton- and γ-emission and from the measured half-life of 102(2) ms, is compared to results obtained from large-scale sd -shell model calculations. A systematic underestimation of the measured strength by the theory is found.

A new measurement of 7Be(p,γ)8B cross section and its astrophysical meaning

Abstract We measured the 7Be(p,γ)8B cross section from Ep = 221 keV to 1376 keV. A uniformly distributed beam that illuminated the whole area of a small diameter target was used to eliminate systematic error from 7Be target non-uniformity. The energy loss profile of the target to the incident beam was measured using the 7Be(α,γ)11C resonance at Eα = 1376 keV. The (α,γ) measurement also demonstrated that the target had a high 7Be atomic purity. The measured yield of the detected 8B was normalized to the activity of the target and the solid angle of the counting detector. Corrections for 8B decay during bombardment and arm rotation were applied. For the first time, the correction due to lost 8B from backscattering was determined experimentally. A new experiment is presently underway, extending to lower proton energy. Due to a problem in the determination of the α-detector solid angle in the first measurement, the solid angle in the new measurement will be determined by a different technique using a 148Gd α source and a silicon detector whose distance to the source can be precisely adjusted.

A new determination of the astrophysical S-factor for the 7Be(p,γ)8B reaction from direct cross section measurements

We measured the 7Be(p,γ)8B cross section from Ēcm=186 to 1200 keV, with a statistical-plus-systematic precision per point of better than ±5%. All important systematic errors were measured including 8B backscattering losses. We obtain S17(0)=22.3±0.7(expt)±0.5(theor) eV-b from our data at Ēcm⩽300 keV and the theory of Descouvemont and Baye.

37Ca β+-Decay: Is the GT Strength Really ‘Quenched’?

The efficiency of the Homestake Mine 37Cl solar v-detector is calibrated[1] using transition rates measured in the β+ decay of 37Ca.