The attenuation of X-radiation generated at constant potentials sufficient to excite K-radiation in a tungsten target

Abstract

Results of a recently described method of calculating the attenuation of the exposure-rate of X-radiation generated a t a constant potential are compared with published experimental data for radiation generated at tungsten targets by potentials above 69.5 kV, the V C ' K-absorption edge. It is shown that the K-radiation does not provide a satisfactory explanation for the slightly but consistently greater penetration observed experimentally, and that there is evidence that this is due to an initial loss of the less energetic bremsstrahlung by absorption within the target.

A determination by an analysis of X-ray attenuation in aluminium of the intensity distribution at its point of origin in a thick tungsten target of bremsstrahlung excited by constant potentials of 60-140 kV

“…These results strongly suggest that a small percentage of K-fluorescence radiation from the target material is present in radiation excited at the higher potentials, in marked contrast to our earlier finding (Soole 1971) that it was necessary to suppose that as much as 90% of the radiation consisted of W K-fluorescence radiation if its observed penetrating power were to be explained.…”

“…However, although agreement with published experimental data was reasonably good (Soole and Jager 1970), it was found subsequently (Soole 1971) that this was somewhat fortuitous, the measurements considered having been normalized to a total filtration of only 2.273 m air + 0.2 mm AI (273.9 mgcm-2 air+ 54 mg cm12 Al) a thickness which allowed the penetration of some softening tungsten L-radiation originating in the target. Removal of this by normalization of the data to the greater thickness of 2.273 m air + 0.5 mm Al (subsequently increased to 2.273 m air + 1.0 mm A1 (Soole 1976)), showed the radiation to be distinctly and consistently more penetrating than the computations predicted.…”

“…Removal of this by normalization of the data to the greater thickness of 2.273 m air + 0.5 mm Al (subsequently increased to 2.273 m air + 1.0 mm A1 (Soole 1976)), showed the radiation to be distinctly and consistently more penetrating than the computations predicted. As it was shown (Soole 1971) that this was true at exciting potentials below 69.5 kV, it could not be due entirely to the presence of tungsten K-radiation from the target, but appeared to result from absorption by the target material, an effect not allowed for in the derivation of Kramers. The same conclusion that target absorption hardened the radiation relative to predictions based upon the Kramers formula had been reached by Jennings (1953).…”

“…This is because, although the characteristic radiation is a very small part of the total, especially when expressed in units of exposure rate close to the target surface, it is very much more penetrating, and especially so at the lightest filtrations, so that when it is removed the effect upon the uncorrected curves is to pull them down at the right-hand, high photon energy, end. It is of interest to note that an earlier attempt (Soole 1971) to show the existence of W K-radiation in the presence of target absorption (for Thoraeus's 100 kV,, results) was unsuccessful, the effect upon the theoretical attenuation characteristics of adding a small amount of W K-radiation to the theoretical bremsstrahlung being to increase slightly rather than to diminish the RMS %A.…”

Deblurring of x‐ray spectra acquired with a Nal‐photomultiplier detector by constrained least‐squares deconvolution

“…Kramers' early theory describing the bremsstrahlung spectrum generated by an x-ray tube neglected target attenuation and assumed a constant value for the differential cross-section coefficient used to calculate the intensity of emitted photons at the point of production. 19 One of the earliest models for spectrum calculation [20][21][22] was based on data from Kramers' theory adjusted for absorption within the target. Calculated data were compared to attenuation measurements to determine the differential energy intensity of bremsstrahlung production.…”