The effect of low-temperature electron irradiation on lutetium and its hydrogen solid solutions

Lutetium metal and several Lu(H) solid solutions are irradiated with electrons in the energy range 0·4 to 1·7 MeV at liquid-helium temperatures. The threshold energy for the displacement of a Lu atom is determined to Td = (17 ± 1) eV, corresponding to an incident electron energy of Ed = (780 ± 30) keV. Displacement cross sections are fitted to the experimental data, with ϱ ≈︁ (60 to 90) μΩ cm/at% F.P. as Frenkel-pair resistivity. The defect production rates at 0·4 MeV of Lu(H) depend on the H-concentration in the α-phase. From their fluence dependence, the concentration dependent defect formation cross sections, σH = (2.35 to 4.18) × 106 barns, are deduced and the defect resistivities, ΔϱH = (36 to 41) μΩ cm/atom H. A comparison with calculated electron-hydrogen scattering cross sections permits to determine a threshold energy for the H-defect formation, TH = (0.06 to 0·09) eV, which, consequently, also varies with the H-concentration. A possible model assuming a paired hydrogen configuration as the stable low-resistivity form at low temperatures is suggested.