A theoretical study of radiation outputs and qualities from a beryllium window tube operated at low kilovoltages (10-50 kVp).

Abstract

An attempt is made to apply some theoretical data regarding continuous X-ray spectra, due to H. A. Kramer, to the conditions obtaining in the use of low kilovoltage beryllium window tubes. Thus, after introducing the appropriate absorption coefficients, transmitted spectral dose rate distributions are computed for selected absorbers (beryllium, aluminium and air thicknesses). Thence, relative outputs and qualities relating to constant potential generation are derived by graphical integration. These results are then extended to pulsating tension units by applying the data to the actual kV and tube current waveforms to which the experimental equipment used by the writer is subject. By this means dose rate waveforms are obtained and their relative areas provide the relative outputs under pulsating tension which can be compared with the corresponding experimental data previously published. From a consideration of relative quality data, a correction for the self-hardening effect of the cathode beam target-penetration is made in terms of an equivalent filtration. The dependence of output on tube current, and air absorption losses are also analysed. The ranges considered are (1) 10 to 50 kVp; (2) 0 to 2 mm Al external filtration (1 mm Be. inherent filtration); (3) 2·5 to 50 mA tube current; (4) 10 to 50 cm F.S.D.