A Comparison of X-ray Standards

Anniversary Paper: Fifty years of AAPM involvement in radiation dosimetry

“…Good agreement ͑Ϯ1%͒ between the standards chambers of several national laboratories in the energy range of 100-180 kV was reported by Taylor in 1931 but was later shown to be incorrect. Errors in the U.S. and British x-ray standards of the order of 1.5% and 2.5%, respectively, were reported in 1954 by Wyckoff et al 19 American physicists, especially those at the NIST, made major contributions to the standardization of x-ray measurements using free-air chambers as further described in Sec. VI below.…”

Primary and secondary standards of roentgen radiation

“…When calibrating substandard thimble chambers for response to roentgen rays in the range 1 mm A1 to 15 mm Cu, it is necessary to use two primary standard ionization chambers of completely different design. Large jumps have been reported (8) in the values of quality correction factors when proceeding from 1 mm Cu HVL to 10-15 mm Cu, and it is not altogether clear whether such large changes are caused by the nature of the sub-standard thimble chamber or by the discontinuity in standardization procedure.…”

An Intercomparison of the Roentgen Standards of Great Britain and U. S. A.

“…An isometric sketch and some details of the NBS chamber have been published (WYCKOFF, ASTON and SMITH 1954;WYCKOFF and ASTON 1954). The only significant changes which have been made since 1953 are that an additional set of guard-wires have been fitted, the distance from the chamber aperture to the collector electrode has been reduced and the scattering diaphragm has been removed, and there is a new capacity compensator with a vibrating reed electrometer as a null instrument.…”