Thermoelastic Response of Polycrystalline Metals to Relativistic Electron Beam Absorption

Abstract

A model is presented for the one‐dimensional thermoelastic response of homogeneous isotropic metals to pulsed relativistic electron beam absorption. The effect of the time dependence of the electron power pulse was examined for two cases: a delta function and a rectangular pulse of duration τ₀. Equations were obtained in both cases which explicitly relate properties of the electron beam (energy absorption profile, total energy, and pulse duration) to properties of the material (density, dilatational wave velocity, and Grüneisen parameter). Experiments were performed to test the developed model for polycrystalline aluminum, copper, and tantalum. Electron beam dosimetry was accomplished by means of calorimetry and a passive film technique. Material response data was obtained by measuring the back surface motion by means of a laser interferometer. The experimental results indicated that an assumption of instantaneous energy deposition was incorrect except possibly for the case of the lowest Z metal, i.e., aluminum The assumption of a rectangular power pulse was adequate to correlate the experimental results for all of the metals. The experiments afforded a direct determination of the Grüneisen parameters which agree with the values calculated from thermodynamic data.