Determination of Certain Spectral Distributions of Soft X Rays by Theoretical Analysis of Absorption Experiments

Abstract

The temperature of a blackbody source which emits continuous radiation with a spectral peak in the range 0.6 to 8 kev in photon energy (soft x rays) may be determined by analyzing an absorption experiment. The technique employed here may be useful for the analysis of other continuous radiation distributions of soft x rays (e.g., free-free continuum radiation from plasma discharges and deceleration radiation from thick targets). Use is made of the approximation that over a limited energy region the absorption coefficient varies inversely with the cube of the spectral energy. The following equation, I(x)=I0(1+C1x logex+C2x+C3x43),neglecting terms of magnitude C4x5/3 or less for thin absorbers, describes the relative dependence of the transmitted x-ray intensity I(x) on the absorber thickness x for a blackbody spectrum of incident intensity I0. The constants C1 through C3 are related in a known manner to the temperature of the blackbody source for a given absorber material. Similarly, the equation, I(x)=I0D1x7/8(1+D2x−1/4) exp(−D3x1/4),neglecting terms of magnitude D4x−1/2 or less for thick absorbers, describes the transmission of a blackbody spectrum characterized by a source temperature which may be determined from the constants D1 through D3.