Reciprocity Law for X-Rays* Part I: Validity for High-Intensity Exposures in the Negative Region

A 50-kv beryllium window x-ray tube was used to confirm the validity of the reciprocity law for x-radiation over an exposure rate range from approximately 0.033 r/sec to approximately 1100 r/sec for the ascending branches of the characteristic curves of two widely used radiation monitoring films. A fast rotary shutter producing pulses of ten microseconds in duration facilitated the coverage of this 1:30 000 range. Conventional x-ray development as well as surface and internal development were employed. From the absence of reciprocity-law failure in the ascending branches of the characteristic curves the conclusion is drawn that, under the present experimental conditions, luminescence does not compete with the photographic effect.