FT VALUE OF SUPERALLOWED FERMI BETA DECAY 26MAL(BETA+)26MG

The threshold for the reaction 26Mg(p, n)26mAl has been measured in terms of the accurately known energies of the α-particle groups from a ThC source. The result Eth = 5208.5 ± 1.7 keV corresponds to a Q-value of -5013.5 ± 1.6 keV. The weighted mean of this and an earlier independent Q-value measurement gives for the end-point in the beta decay 26mAl(β+)26Mg the result 3208.6±1.3 keV. The half-life for the beta decay has been measured as 6.346±0.005 sec. The ft value for the transition is thus found to be 3081±7 sec, including radiative corrections. This result is lower than those for other superallowed Fermi decays. It corresponds to a value for the vector coupling constant Gβv = (1.4129±0.0016) x 10-49 erg · cm3. The value inferred for the Cabibbo angle is cosθβv = 0.985±0.001, excluding uncertainties in the radiative corrections. This result appears to differ appreciably from the value inferred from the rate of K+ → π0e+ v decay. © 1969.