Effect of pressure on the decay rate of ~7Be

摘要

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-λ_0)/λ_0 = (4.87 * 10~(-5))P-(5.9 * 10~(-8))P~2, 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 ~(40)K to ~(40)Ar, which has been widely adopted to date geological events.