Effect of Hydrostatic Pressure on the Recovery of Electrical Properties of Neutron-Irradiated Molybdenum

High-purity molybdenum has been irradiated at 40\ifmmode^\circ\else\textdegree\fi{}C to a fluence of 6.2\ifmmode\times\else\texttimes\fi{}${10}^{18}$ n/${\mathrm{cm}}^{2}$ ($E>1$ MeV) and subsequently isochronally annealed at two pressures, \ensuremath{\le}1 and 20 000 bar. At low pressure, the electrical resistance increase recovers in three stages, at 150, 425, and 575\ifmmode^\circ\else\textdegree\fi{}C. The effect of pressure is to lower the 150\ifmmode^\circ\else\textdegree\fi{}C recovery peak to 90\ifmmode^\circ\else\textdegree\fi{}C; this shift implies a negative activation volume of migration of -0.9 molar volumes for the migrating defect. The 425\ifmmode^\circ\else\textdegree\fi{}C peak is apparently also lowered by pressure, but because of its small magnitude and uncertainty in its position, more detailed data are required before any pressure coefficient can be determined. The final 575\ifmmode^\circ\else\textdegree\fi{}C recovery peak is lowered to 375\ifmmode^\circ\else\textdegree\fi{}C under pressure and displays a pressure coefficient of -10\ifmmode^\circ\else\textdegree\fi{}C/kbar.