Effect of pressure on the decay rate of 7Be

Beryllium-7 in Be(OH)2 gel was compressed in diamond-anvil pressure cells up to 442 kbar at room temperature. By counting the activity of 7Be, the decay rate for the conversion of 7Be to 7Li via electron capture was measured. The decay constant of 7Be, λ, was found to increase, but the rate of increase decreased with increasing pressure. A quadratic regression of the data yields (λ−λ0)/λ0=(4.87×10−5)P−(5.9×10−8)P2, where the subscript zero denotes zero pressure and P stands for pressure in kilobar. Thus, λ of 7Be increases by about 1% at 400 kbar. The observed data set can be rationalized by an increase in electron density near the nucleus of 7Be at high pressures. This result may bear some implications for the conversion of 40K to 40Ar, which has been widely adopted to date geological events.