Excerpt from A Basis for the Comparison of X-Rays Generated by Voltages of Different Wave Form This conductivity 1s, for any given wave length or any given spectral distribution, very closely proportional to the intensity.1 Since, how ever, the factor of proportionality varies With the wave length, the ionization chamber indications do not serve to, give the relative i1iten sities of different spectral distributions. The conductivity imparted to air by radiations having different spectral distribution 1s, probably, a better measure than intensity of their relative therapeutic value; hence, the conductivity of air, expressed ln roentgens per unit time, has been internationally adopted as the physical unit of measure of an X-ray dose. But, even ln dosage, it is important to realize that the same number of roentgens represents the same dose only when the spectral distribution of the radiations is the same.
The spectral distribution of intensity is represented by a curve, throughout the spectrum, plotted as a function of the wave length or the frequency. Its direct determination 1s cumbersome and subject to considerable error. In practice, it is inferred as quality (or hard ness) from the thickness of an absorber, say copper, required to reduce the number of roentgens in the radiation to One half. This thickness is called the half value layer. 2 More complete information of the 3spectral distribution 1s inferred from the complete absorption curve, 3obtained with a series of thicknesses of the absorbing mate rial. 4 5 6 In fact Silberstein,7 has shown that the complete spectral distribution curve neglecting characteristic lines IS obtainable from an exact absorption curve.
About the Publisher
Forgotten Books publishes hundreds of thousands of rare and classic books.
This book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully; any imperfections that remain are intentionally left to preserve the state of such historical works.
