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ETUDE D'UN DOSIMETRE DE TRANSFERT ADAPTE A LA DETERMINATION DES DOSES ABSORBEES DANS LES TISSUS A PROXIMITE DES SOURCES DE RAYONNEMENT BETA

Objective

STAFF WORKING IN CLOSE PROXIMITY TO OR IN CONTACT WITH MATERIALS EMITTING BETA RADIATION ARE EXPOSED TO CONSIDERABLE RADIATION RISKS.
FROM THE POINT OF VIEW OF RADIATION PROTECTION IT IS NECESSARY TO KNOW TO WHAT EXTENT THE GEOMETRICAL CONFIGURATION OF IRRADIATION AND THE SPECTRAL DISTRIBUTION OF THE BETA RADIATION EMITTED INFLUENCE THE MEASUREMENTS CARRIED OUT BY DOSIMETERS USED FOR RADIATION PROTECTION. THE RADIATION PROTECTION SERVICE HAS FOR SEVERAL YEARS BEEN ENGAGED IN RESEARCH INTO THE PROBLEMS POSED BY BETA RADIATION DOSIMETRY.
IN THE FRAMEWORK OF A PREVIOUS CONTRACT (B10-A-523-F), THE LABORATORY HAS STUDIED THE RESPONSE OF SEVERAL CURRENTLY-USED RADIOPROTECTION INSTRUMENTS IN BETA RADIATION BEAMS EMITTED BY DIFFERENT RADIOACTIVE ELEMENTS (147 PM, 204 TL AND 90 SR + 90 Y) FOR VARIOUS GEOMETRICAL CONFIGURATIONS: POINT SOURCE, EXTENDED PLANE SOURCE OF 60 CM MAXIMUM DIAMETER, DIFFUSE BEAMS PROVIDING UNIFORM IRRADIATION.
STUDY OF THE PERFORMANCE OF AN EIC-TYPE VARIABLE-CAVITY FWT CHAMBER USED AS A REFERENCE DETECTOR FOR CHARACTERIZING THESE BEAMS HAS REVEALED THE LIMITS TO USING THIS DETECTOR IN THE CASE OF NON-HOMOGENEOUS IRRADIATION (DISTANCE FROM SOURCE LESS THAN THREE CENTIMETERS).
THE LABORATORY INTENDS TO STUDY A TRANSFER DOSIMETER WHICH, CALIBRATED WITH RESPECT TO THE VARIABLE-CAVITY CHAMBER IN HOMOGENEOUS IRRADIATION, WOULD ALLOW BETA RADIATION BEAMS BY SOURCES TO BE CHARACTERIZED UP TO THE TIME OF CONTACT.
THIS CONTRACT WILL PROVIDE MORE INFORMATION ON DOSIMETRY FOR THE PROTECTION OF WORKERS AND THE POPULATION.DEVELOPMENT OF DOSIMETRIC METHODOLOGY FOR A BETTER EVALUATION OF ORGAN DOSES.
THIS PROPOSAL WILL PROVIDE MORE INFORMATIONS ON DOSIMETRY FOR THE PROTECTION OF WORKERS AND THE POPULATION. DEVELOPMENT OF DOSIMETRIC METHODOLOGY FOR A BETTER EVALUATION OF ORGAN DOSES.
Owing to the impractical nature of extrapolation chambers, experiments have been carried out using lithium fluoride and thermally stimulated exoelectron emission (TSEE) dosimeters. Lithium fluoride disks work well at small distances from the strontium 90 and ytterbium 90 and titanium 204 radioactive sources. However, TSEE beryllium oxide dosimeters seem, at present, unsuitable for radioprotection of low linear energy transfer (LET) particles, because of their dispersion properties. Experiments are still in progress with the Vinten extremity dosimeter and the radionuclide plutonium 147.

Experiments have been directed at the evaluation of the uncertainties in beta absorbed doses measured with currently used extremity dosimeters, and the possibility of using an extrapolation chamber as a reference detector and thermally stimulated exoelectron emission (TSEE) or ultrathin thermoluminescence (TL) dosemeters as transfer instruments.
THE WORK COULD BE DIVIDED UP AS FOLLOWS:
A. PRELIMINARY RESULTS OBTAINED WITH A DOSIMETER BASED ON THE EXOELECTRONIC EMISSION OF LITHIUM FLUORIDE AND DEVELOPED BY THE LABORATORY, PROVING THE VALUE OF SUCH A DETECTOR FOR BETA RADIATION DOSIMETRY.
A MORE DETAILED STUDY OF THE CHARACTERISTICS OF THIS DOSIMETER WOULD BE CARRIED OUT (REPRODUCIBILITY, RESPONSE AS A FUNCTION OF THE ENERGY AND THE ANGLE OF INCIDENCE OF THE BETA RADIATION, ETC.).
B. STUDY OF THE POSSIBILITIES OF USING AS A TRANSFER DOSIMETER VARIOUS DETECTORS DEVELOPED IN OTHER LABORATORIES (EXOELECTRONIC EMISSION DOSIMETER - BEO, ULTRA-THIN THERMOLUMINESCENT DOSIMETER, VINTEN).
C. USING THESE DIFFERENT DOSIMETERS, CHARACTERIZATION OF THE BEAMS DESCRIBED ABOVE BY TISSUE DOSE AND COMPARISON WITH THE THEORETICAL VALUES ESTABLISHED BY CROSS.
D. DETERMINATION OF THE RESPONSE TO BETA RADIATION OF RADIATION PROTECTION INSTRUMENTS AND DOSIMETERS IN CURRENT USE, IN BEAMS THUS CHARATERIZED FOR A GEOMETRY OF SOURCE PROXIMITY.
THIS LAST STAGE WOULD BE ESSENTIAL FOR EVALUATING THE MEASUREMENT ERRORS OF THE DOSIMETERS GENERALLY USED IN EXTREMITY DOSIMETRY.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

Commissariat à l'Energie Atomique (CEA)
Address
Centre D'études De Grenoble Avenue Des Martyrs
38041 Grenoble
France