Electron capture decay of ⁷Be encapsulated in C₆₀: Origin of increased electron density at the ⁷Be nucleus

We offer a new theoretical interpretation for the effect of enhanced electron density at the ⁷Be nucleus encapsulated in fullerene C₆₀. Our ab initio Hartree-Fock calculations show that the electron density at the ⁷Be nucleus in ⁷Be@C₆₀ increases due to the attractive effective potential well generated by the fullerene. The 2s state in the isolated Be atom turns into a 3s state in the joint potential. This new state has higher energy and slightly larger amplitude at the Be nucleus than the previous 2s state. Moreover the 3s wave function has an additional node that appeared at a distance r5a_B from the center. The node imitates repulsion between the Be electron and the fullerene wall because the electron has zero probability to occupy this region. Such an imitation of the repulsion by means of the node in an attractive potential has a direct physical analogy in the theory of - and N-N nuclear interactions. ©2010 The American Physical Society