Application of the half-filter method to the flash radiography using a neutral filter in the range of x-rays

Abstract

Application of the half-filter method to the flash radiography using a neutral filter in the range of X-rays J-L. GERSTENMAYER P. VIBERT Centre d'Etudes de Vaujours, CEA AB STRACTThe purpose of this paper is a new application of the already known in optics half-filter bootstrap method in the frame of radiography in order to calibrate X film pack detectors. The key to this method is the practical calculation of a "grey filter" in the range of hard X rays (1MeV maxi.). INTRODUCTIONUsing X rays to make a quantitative analysis of the areal masses of irradiated objects requires a previous calibration of the screen film receptor. Currently used methods [1] need a reproductible, isotropic, monoenergetic radiation source. Such conditions are rarely met in flash radiography, and it may be uneasy for the radiologist to calibrate film-packs receptors. Thus we have tried to adapt the already known in optics half filter method: one can expose differently two receptors, looking at the same object and thus containing the same information. Between this two receptors is insert a grey filter (spectraly neutral) with a well known k transmission coefficient. Each point of the second film receives a flux equal to k times the one of the first film (k < 1).The characteristic Optical Density-Log(Erei) relative calibration curve is then determined by a bootstrap niethod (recurrence).This method requires only an accurate knowledge of the /c coefficient and allows to obtain the receptor film response from a single flash, neither calibrated nor isotropic in flux, in the hard X rays range (about 1 MeV). The object which is analysed by radiography provides a sufficient modulation of the radiation field to encompass the usefull density range of X rays film-pack.This method of calibration is only relative or implies as known the relationship between the received X ray intensity and the illumination secondly produced by the intensifying screen. 286 / SPIE Vol. 1346 Ultrahigh-and High-Speed Photography, Videography, Photonics, and Velocimetry '90 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/21/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx

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“…In a previous paper we have suggested an original calibration set up called "half filter method" , which use a grey (spectrally neutral) X-rays filter, to convert optical density to relative deposited X-fiuence [3]. The key of this method is the computation of the filter attenuation coefficient.…”