A NEW MEASUREMENT OF FT VALUE FOR MIRROR DECAY 35AR(BETA+)35CL AND A CALCULATION OF VECTOR COUPLING CONSTANT

Accurate measurements have been made of the threshold for the reaction 35Cl(p, n)35Ar, and of the branching ratios and half-life in the decay 35Ar(β+)35C1. The threshold, 6941.2 ± 1.7 keV leads to the value 4941.6 ± 1.7 keV for the beta end-point in the ground state decay of 35Ar, and the corresponding f-value is 3112.3 ± 5.0. The result obtained for the branching ratio for the ground state decay was 98.54 ± 0.05 %. The half-life measurements gave the result t 1 2 = 1.770 ± 0.006 sec. After application of a radiative correction of + 1.45 %, the ft value for the mirror transition was thus determined to be 5671 ± 21 sec, excluding uncertainties in the radiative correction. This value is much more accurate and significantly lower than previous measurements. When combined with the result of Calaprice et al. for the spatial asymmetry of positons from the decay of nuclear spin polarized 35Ar, the present ft value leads to a value for the weak interaction vector coupling constant in beta decay of Gβv = (1.460 ± 0.006) × 10-49 erg · cm3. This value is seriously out of line with results obtained from J = 0+, T = 1 decays, and from other mirror decays. Further experimental work, particularly on the branching ratios and the asymmetry measurement are indicated, as well as considerations of possible nuclear structure or other effects. © 1969.