On the Adequacy of Half-value Layer as a Criterion of X-ray Quality in the Calibration of Dosemeters

Five thimble ionization chambers were compared with a free-air chamber using X rays produced at 20 to 55 kV with half-value layers between 0·05 and 0·20 mm Al. One chamber showed a difference of nearly 4 per cent in its correction factor for beams of the same H.V.L. produced at 20 and 55 kV. With this single exception H.V.L. appeared to be an adequate criterion of X-ray quality for the calibration of ionization chambers.