Direct observation of two protons in the decay of 54Zn.

The two protons emitted in the decay of 54Zn have been individually observed for the first time in a time projection chamber. The total decay energy and the half-life measured in this work agree with the results obtained in a previous experiment. Angular and energy correlations between the two protons are determined and compared to theoretical distributions of a three-body model. Within the shell model framework, the relative decay probabilities show a strong contribution of the p2 configuration for the two-proton emission. After 45Fe, the present result on 54Zn constitutes only the second case of a direct observation of the ground state two-proton decay of a long-lived isotope.

First direct observation of two protons in the decay of 45Fe with a time-projection chamber.

The decay of the ground-state two-proton emitter 45Fe was studied with a time-projection chamber and the emission of two protons was unambiguously identified. The total decay energy and the half-life measured in this work agree with the results from previous experiments. The present result constitutes the first direct observation of the individual protons in the two-proton decay of a long-lived ground-state emitter. In parallel, we identified for the first time directly two-proton emission from 43Cr, a known beta-delayed two-proton emitter. The technique developed in the present work opens the way to a detailed study of the mechanism of ground state as well as beta-delayed two-proton radioactivity.

Personal exposure to elements in Mexico City air.

Personal exposures to various metals in airborne particulates in Mexico City were measured over a seven consecutive-day period. Subjects were divided into two groups, Group A, whose work required them to spend considerable time outdoors and in traffic (messengers, delivery men, taxi drivers, salesmen), and Group B who spent most of their time indoors (university professors, consultants, managers and research workers). Group A spent 32 +/- 8.5% of their time outdoors, while Group B spent 10.7 +/- 6.7% of their time outdoors. Group A had higher exposures to airborne lead, zinc, vanadium, manganese and chromium than did Group B. There was no difference between the groups with respect to airborne copper exposures. Overall exposures to the various airborne metals were: lead, 435 +/- 220 ng m-3; zinc, 361 +/- 253 ng m-3; vanadium, 23 +/- 12 ng m-3; manganese, < or = 30 +/- 25 ng m-3; chromium, < or = 8.5 +/- 5.5 ng m-3; and copper, < or = 45 +/- 32 ng m-3. A significant number of samples were below the analytical limits of detection for manganese and copper.