Low temperature relaxations associated to quantum tunnelling of H in Sc and Y

Acoustic spectroscopy and electrical resistivity measurements have been employed to investigate the two relaxation processes occurring at liquid He temperature in very dilute Y-H and Sc-H alloys, and ascribed to H tunnelling systems near single or paired O traps. At very low H concentration, the peak due to the O-H tunnelling system becomes extremely narrow and is describable in terms of incoherent tunnelling with phonon assisted transitions.