Modifying the electron capture decay rate of Be 7 by using small fullerenes

Electron capture (EC) decay of a Be7 atom, the rate of which is affected by the electron density at the Be7 nucleus, forms a Li7 atom and emits a neutrino. Herein, we studied the EC decay rate of Be7@C2n (2n=24, 28, 32, 36, 50), in which those fullerenes have enhanced stability relative to their near neighbors, by using ab initio calculations. The stable and metastable Be7 atom sites and electron density at the Be7 nucleus in Be7@C2n were calculated. Unlike Be7@C60, the Be7 nucleus sites in Be7@C2n (2n=24, 28, 32, 36, 50) are always off center and close to the fullerene cage. Due to the bonding interaction between Be7 and the fullerene cage, the electron density at the Be7 nucleus in Be7@C2n is smaller than those of a single Be7 atom and of Be7 in Be7@C60, leading to the result that the half-life of Be7 in Be7@C2n increases. Based on equilibrium statistical thermodynamic calculations, the temperature effect on the half-life of Be7 has been analyzed. In contrast to Be7@C60, the temperature only slightly influences the half-life of Be7 in Be7@C2n suggesting that the EC decay rate of Be7 could be precisely modified by using small fullerene cages.