X-ray or gamma ray systems or devices – Specific application – Absorption
Patent
1986-07-07
1988-08-16
Church, Craig E.
X-ray or gamma ray systems or devices
Specific application
Absorption
378156, 378185, 378145, 2504821, 2504831, G01N 2304
Patent
active
047649461
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to a method for influencing the effect of X-ray or gamma radiation on a target sensitive to the radiation, preferably for selective modification of an image of an object formed on a target by X-ray or gamma radiation, as well as to a modifying body for implementing the method according to the invention.
BACKGROUND ART
For producing radiographs, amplifying foils are known which convert the incident X-ray radiation into a radiation falling in the range of visible light. In general, these amplifying foils used to be arranged before and behind the film to be shot. In this case blackening of the film is primarily caused by the radiation falling into the visible range. Application of amplifying foils enables reduction of exposure time, however, it is accompanied by a loss in the sharpness of the image.
From the PCT Application PCT/HU83/00062 published under the number WO 84/02399 a method for producing radiographs is known, in which a modifying body of laminar structure is placed between the object to be examined and the film. The modifying body consists of thin Pb layers arranged on one another, which are applied onto a carrier sheet. If in the object examined material thickness corresponding to different ray paths is changing, e.g. the object is a pipe, the modifying body automatically acts as a compensator. In such a manner, on the image thus obtained far more details of the object can be seen and evaluated, however, the exposure times have to be increased.
In radiologic practice materials of the films used for preparing radiographs respond only to an X-ray or gamma radiation, the energy of which surpasses a given limit of energy level. In general, sensitivity is the highest immediately above said energy level, thereafter with increasing energy it drops considerably. Just in order to eliminate this dependency on energy, sensitivity of usual films used to be modified by means of filters so as to achieve nearly equal sensitivity in a broader range of energy. This, however, involves a poor sensitivity of the film in the whole energy range, requiring an increased radiation intensity or a longer exposure time in preparing radiographs.
DISCLOSURE OF INVENTION
The aim of the invention is to develop a method and means, by the aid of which an image formed by X-ray or gamma radiation can be advantageously influenced so that quality of the image could be improved without prolonging the exposure time, and if possible, even with a shorter exposure period.
Accordingly, the invention relates to a method for influencing the effect of X-ray or gamma radiation on a target sensitive to the radiation, preferably for selective modification of an image of an object formed on a target by X-ray or gamma radiation, in the course of which a modifying body having laminar structure is arranged in front of the target in the path of the radiation beam. The improvement according to the invention is that in front of the target at least two layer groups are disposed, each of said layer groups comprises a plurality of superimposed layers emitting a secondary radiation under the influence of the primary radiation or the secondary radiation of the previous layer group, respectively, the energy of which is lying above the absorption energy level defined by the electron shell K of an element being present in the following layer group or in the target arranged behind the last layer group, respectively.
By proper selection of the material of said layer groups it can be achieved that at least a part of the primary X-ray or gamma radiation is converted gradually within the layer groups into a radiation with an energy range in which the sensitivity of the target is maximal. By the better utilization of the target a reduction of exposure time becomes possible. The target can be a film being sensitive to X-ray or gamma radiation or a screen or any image-sensing means, e.g. a NaI or CsI crystal detector doped by Tl.
It has also been recognized that it can be advantageous, if a layer group is disposed in front
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"Definition and Measurement of Means of Filtered X-Radiation", by Grudskii et al., Pribory i Tekhnika Eksperimenta#4, 7-8, 1974.
"Balanced Filters for Silver K.sub..alpha. X-Rays", by Berman et al, Review of Sci. Instruments, vol. 41, No. 6, Jun. 1970.
Radiation Defectoscopy, 2nd Edition, Roumyantsev, S.V., pp. 158-159 and 195-200, Moscow, Russia, 1974 (English Translation Attached).
Church Craig E.
Freeman John C.
Innofinance Altalanos Innovacios Penzwtezet
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