Endohedral incorporation of argon atoms into C60 by neutron irradiation

It is demonstrated that by neutron irradiation of polycrystalline C60 in an argon atmosphere or of C60 crystals containing absorbed or adsorbed argon, a stable endohedral argon compound is formed. The concentration of argon has been determined by instrumental neutron activation analysis via the short-lived 41Ar isotope. It is supposed that the endohedral compound is formed by penetration of the argon atom into the C60 cages; a mechanism due to the high kinetic energy recoiling 41Ar atoms according to the 40Ar(n, γ)41Ar nuclear reaction seems the most plausible.