1982 Volume 17 Issue 2 Pages 143-150
The collection efficiency, f-value, of a parallel-plate ionization chamber exposed to diagnostic X-rays has been numerically obtained. The results of calculations show that the f-value deviates from the well-known Boag's formula when the pulse duration becomes of the same order of the ion transit time between the electrodes. Furthermore, the effects of the pulse shape on the f-value and the output currents have been clarified.
The output currents and the saturation curves have been measured in fields generated by an X-ray tube for medical diagnosis. There found a good agreement between experimental and calculated results. The true f-value has been determined by the saturation curve method previously reported. It was concluded from the experimental confirmation of the inverse square law of the exposure that the method was useful for diagnostic X-rays.
