X-ray spectra and gamma factors from 70 to 120 kV X-ray tube voltages

Abstract

The energy distribution of photons (spectrum) produced in X-ray generators, or X-ray tubes, depends on current, voltage and the target/filter combination; in turn, the dose depends on the spectrum. During the X-ray tube operation, the dose is due the direct beam or useful beam, the leaking out from the X-ray unit, and those photons scattered by the patient. The dose rate must be reduced to allowable limits using a shielding. In the shielding design an important parameter is the dose normalized to the current and the time, that in this work we named Gamma factor, as the factor used for gamma-ray sources. In this work analog Monte Carlo methods were used to calculate the photon spectra and the Gamma factors for air-Kerma and the Ambient dose equivalent for 70, 80, 90, 100 and 120 kV X-ray tubes having tungsten target and aluminum filter. The mean energies of photon spectra were calculated and the conversion coefficients for H*(10) and Ka per unit fluence were calculated and compared with the coefficients for monoenergetic photons. The glass enclosure and the filter eliminate the low-energy photons; calculated spectra show the continuous X-ray distribution due to Bremsstrahlung and the discrete distribution, due to characteristics X-rays. Photon fluences and doses depend on the X-ray unit voltage. Both gamma factors are similar to values recommended in norms while the fluence-to-dose (Ka and H*(10)) conversion coefficients in function of the mean energy are larger than the fluence-to-dose conversion coefficients for monoenergetic photons.