Experimental validation of the largest calculated isospin-symmetry-breaking effect in a superallowed Fermi decay.

A precision measurement of the γ yields following the ß decay of (32)Cl has determined its isobaric-analogue branch to be (22.47(-0.18)(+0.21))%. Since it is an almost pure-Fermi decay, we can also determine the amount of isospin-symmetry breaking in this superallowed transition. We find a very large value, δ(C) = 5.3(9)%, in agreement with a shell-model calculation. This result sets a benchmark for isospin-symmetry-breaking calculations and lends support for similarly calculated, yet smaller, corrections that are currently applied to 0+ → 0 + transitions for tests of the standard model.

12C+12C fusion reactions near the Gamow energy.

The fusion reactions 12C(12C,alpha)20Ne and 12C(12C,p)23Na have been studied from E=2.10 to 4.75 MeV by gamma-ray spectroscopy using a C target with ultralow hydrogen contamination. The deduced astrophysical S(E)* factor exhibits new resonances at E< or =3.0 MeV, in particular, a strong resonance at E=2.14 MeV, which lies at the high-energy tail of the Gamow peak. The resonance increases the present nonresonant reaction rate of the alpha channel by a factor of 5 near T=8x10(8) K. Because of the resonance structure, extrapolation to the Gamow energy EG=1.5 MeV is quite uncertain. An experimental approach based on an underground accelerator placed in a salt mine in combination with a high efficiency detection setup could provide data over the full EG energy range.

Flint mining in prehistory recorded by in situ-produced cosmogenic 10Be.

The development of mining to acquire the best raw materials for producing stone tools represents a breakthrough in human technological and intellectual development. We present a new approach to studying the history of flint mining, using in situ-produced cosmogenic 10Be concentrations. We show that the raw material used to manufacture flint artifacts approximately 300,000 years old from Qesem Cave (Israel) was most likely surface-collected or obtained from shallow quarries, whereas artifacts of the same period from Tabun Cave (Israel) were made of flint originating from layers 2 or more meters deep, possibly mined or quarried by humans.

Precision measurement of the 7Be(p,gamma)8B cross section with an implanted 7Be target.

The 7Be(p,gamma)8B reaction plays a central role in the evaluation of solar neutrino fluxes. We report on a new precision measurement of the cross section of this reaction, following our previous experiment with an implanted 7Be target, a raster-scanned beam, and the elimination of the backscattering loss. The new measurement incorporates a more abundant 7Be target and a number of improvements in design and procedure. The point at E(lab)=991 keV was measured several times under varying experimental conditions, yielding a value of S17(E(c.m.)=850 keV)=24.0+/-0.5 eV b. Measurements were carried out at lower energies as well. Because of the precise knowledge of the implanted 7Be density profile, it was possible to reconstitute both the off- and on-resonance parts of the cross section and to obtain from the entire set of measurements an extrapolated value of S17(0)=21.2+/-0.7 eV b.