Abstract
It is usually assumed that for accurate comparisons of x-ray intensities, the voltage applied to the ionization chamber must be sufficient to reduce the loss of ions by recombination to a fraction of the total number produced, less than the permissible error of measurement. Tests show, however, that under proper conditions the fraction lost may be independent of the total number produced, for any loss up to about 10%. With the chamber used here, this permits accurate comparisions of ionization currents with only 45 volts, instead of the 900 required to reduce the loss to 1%, and thereby minimizes errors due to battery changes. This constancy of the fraction lost, with different currents, probably indicates that the recombination is practically all columnar, as reported by other observers with alpha rays. In the case of x-rays, columnar recombination must be recombination between ions produced by the same photoelectron. This condition must be satisfied best with faint rays, such as are used in x-ray spectrometry. With stronger rays it should break down, and therefore these tests do not indicate anything about ordinary x-ray dosage measurement.
© 1928 Optical Society of America
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