Thermodynamics of refractory nuclear materials studied by mass spectrometry of laser-produced vapors

A new method of high-temperature mass spectrometry (MS) with laser-induced vaporization (LIV) has been developed. The initial problem of LIV MS, consisting of an inadequate correlation between the temperature of the surface and the MS signal, was successfully overcome.The method was developed on graphite, of which fast time-resolved MS measurements (ca. 20 ms) were performed over a large mass interval; the influence of geometrical parameters and of the laser pulse length on MS measurements was studied. Carbon sublimation relative partial pressures of C-1, C-2, C-3, and C-5 were measured up to 3810 K. This corresponds to a total pressure of about 0.8 bar estimated independently by the integral mass flux using the Hertz-Knudsen equation. The vaporization of UO2 was studied at temperatures above approximate to 2500 K, where conventional Knudsen-cell mass spectrometry cannot be applied. The vaporization enthalpy obtained for the main species in UO2 vapor was in good agreement with that of conventional mass spectrometry.