Isotopic effect in the binding of helium in graphite
Khudyakov A. V. , Gabuda S. P. , Savel'ev A. A. , Khudyakov V. A., Semyannikov P. P. , Baskin E. M.
The binding of helium isotopes by graphite has been studied. The thermal desorption of helium after it is introduced into the graphite obeys an Arrhenius law. The desorption activation energies are 8.1 + 1.0 kcal/mole for 3He and 21.0 + 1.3 kcal/mole for 4He. The isotopic effect observed here is explained on the basis of a model of an encapsulation of helium atoms in the volume between graphite layers. The characteristic amplitudes and frequencies of the vibrations of the encapsulated atoms are found.