GB839136A - "radiation dosimetry" - Google Patents

Abstract

839,136. Radiation dose-meters. GENERAL ANILINE & FILM CORPORATION. Oct. 7, 1957 [Oct. 18, 1956], No. 31313/57. Class 98(1) A dosimeter for high energy ionizing radiation falling within a wavelength band of between 0.01 and 0.1 A comprising a housing which is opaque to light but permeable to the radiation and contains light-sensitive material in which exposure to radiation, particularly in the longer wavelength part of the band, produces a visible change; means associated with the light-sensitive material for converting the radiation, particularly in the shorter wavelength part of the band, into actinic rays; a filter for correcting the combined responses of the light-sensitive material and the associated converting material so that the effective response is substantially uniform over the band; and means for visually comparing said exposed material against a standard to determine the extent of the exposure to said radiation. As shown the housing which may be of plastic material consists of telescoping parts 6, 7 having finger-grip ridged portions at 10, 11 to facilitate opening the light-tight tongue and groove latch 9, 8. A circular lead block 15 in the part 6 has a circular recess 16 receiving a piece 17 of radiationsensitive high speed print-out paper e.g. as in Specification 795,042, which is sensitive also to actinic light from a fluorescent crystal 13 mounted in the part 7 and overlying the paper when the housing is in the normal closed position. The crystal chosen e.g. thallium-activated potassium iodide is more responsive to the shorter wavelength end of the band of radiation so that the response curves of the crystal and the paper, which is more sensitive to the longer wavelength end of the band, tend to be mutually compensating, and the effective response curve is made substantially flat by a shield or filter 14 for soft X-rays, e.g. of lead of thickness 0.09 inch, which together the base of the lead block of similar thickness encloses the crystal 13. The sensitivity may be increased by a coating of a light-diffusing substance, e.g. magnesium carbonate, either on the crystal or on the inner face of the shield 14. To find the exposure received by the dosimeter, the housing is slid open when the paper 17 is brought beneath the central aperture within an annular comparison wedge 24 and a covering orange filter 21 through which evaluation is made, both the wedge and filter 21 being carried by a cut-out 18 in the part 7.