Uncertainties which limit the use of the Re-Os isobaric pair as a cosmochronometer for the age of the galaxy and the universe include those of the partial half-lives of the continuum and boundstate decays of Re. While the total half-life of the decay is well established, the partial half-life for the continuum decay is uncertain, and several previous measurements are not compatible with each other. A high-temperature quartz proportional counter has been used in this work to remeasure the continuum decay of Re by introducing a metallo-organic rhenium compound into the counting gas. The measured beta end-point energy for the continuum decay of neutral Re to singly ionized Os of 2.70 + 0.09 keV agrees with earlier results. However, the present half-life measurement of (45 + 3) Gyr agrees within the quoted uncertainties only with an earlier measurement. The new half-life for the continuum decay and the recently reported total half-life of (43.5 6 1. 3) Gyr yield a branching ratio for the bound-state decay into discrete atomic states of (3 + 6) %%uo. This is in agreement with the most recent calculated theoretical branching ratio of approximately 1%.
Very energetic light ions (primarily protons and alphas) with energies often approaching the full beam energy have been observed at or near 0=0' in heavy-ion collisions, Z = 8 to 28, F/A =9 to 40MeV/nucleon from Ta and, in selected cases, Cu targets. Analysis of spectral shapes and angular distributions using a standard moving source model requires that the source velocity approaches the beam velocity as L9~0' and that the spectral slope parameters and apparent source temperatures be increased. Large values for the latter ( T&~16 MeV), which are typically twice as large as those deduced from complex fragment emission, are often required to fit the alpha particle spectra 0=0'.Massive cluster transfer and other quasitransfer mechanisms may provide an alternative model for the generation of the E~Eh", ", alpha particles and other light fragments.
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