ANALIZA KRIVE ISIJANJA TLD - NOVE MOGUĆNOSTI U LIČNOJ DOZIMETRIJI
Marinković Olivera
Institut za medicinu rada i radiološku zaštitu "Dr Dragomir Karajović", Beograd, Srbija i Crna Gora

U ličnoj dozimetriji koriste se razne vrste termoluminiscentnih materijala. Posebnost kristala LiF ogleda se u tome da se kriva isijanja može razložiti na karakteristične pikove, čijom analizom je moguće doći do niza zanačajnih podataka.

CILJ: Cilj nam je prezentirati analizu krive isijanja TLD kao novu mogućnost u kontroli lične dozimetrije.

MATERIJAL I METODE: Laboratorija za ličnu dozimetriju u Institutu za medicinu rada i radiološku zaštitu "Dr Dragomir Karajović" raspolaže sa uređajem za obradu TL dozimetara Harshaw Model 6600. Lični dozimetri imaju dva kristala LiF Tip-100; nose se u kasetama sa filtrima koji omogućavaju određivanje ekvivalentnih doza Hp(0.07) i Hp(10). Za procenu efektivne doze ova laboratorija primenjuje model koji sigurno precenjuje vrednost efektivne doze u rutinskoj obradi dozimetara. Efektivna doze se izjednačava sa ekvivalentnom dozom Hp(10). U slučajevima prekoračenja gornje granice efektivne doze, za procenu se uzima u obzir niz značajnih parametara: korišćenje zaštitne opreme, pozicija dozimetra u odnosu na telo i u odnosu na zaštitnu opremu (iznad/ispod kecelje).

PRIKAZ: Obradom ličnog dozimetra određuju se ekvivalentne doze Hp(0.07) i Hp(10). Količnik ove dve veličine zavisi od energije kojom je dozimetar ozračen. Tako je moguće korišćenjem postojeće kalibracije ustanoviti vrstu izvora zračenja. Analizom (tzv. dekonvolucija) krive isijanja izračunavaju se vrednosti karakterističnih pikova koji omogućavaju procenu trenutka ozračivanja dozimetra. Ovaj deo izračunavanja obavlja se prema postojećoj kalibraciji za grupu ispitivanih dozimetara istog proizvođača i iste šarže dozimetara.

ZAKLJUČAK: Procena trenutka ozračivanja nije moguća ako između ozračivanja i obrade dozimetra protekne više od dva meseca. Zato je stav ove laboratorije da se ukine mogućnost obrade ličnih dozimetara na tri meseca. Za ona radna mesta gde je verovatnoća ozračivanja radnika dozama značajno većim od doza koje potiču od prirodnih izvora zračenja zanemarljivo mala, potrebno je ukinuti zakonsku obavezu redovne obrade ličnih dozimetara.

THE ANALYSIS OF TLD GLOW CURVE - NEW POSSIBILITIES OF PERSONAL DOSIMETER
Marinković Olivera.
Institute of Occupational Medicine and Radiological Protection "Dr. Dragomir Karajović", Belgrade, Serbia and Montenegro

Various types of thermoluminescent substances are used in personal dosimeter. Specificity of LiF crystal reflects in the fact that the glow curve may be deconvoluted to characteristic peaks, whose analysis will yield a series of significant data.

AIM: The aim is to present analyses of TLD glow curve as new possibilities of person dosimeter.

MATERIAL AND METHODS: Laboratory for personal dosimeter at the Institute of Occupational and Radiological Protection possesses a device for analysis of TL dosimeters - Harshaw Model 6600. Personal dosimeter has two type-100 LiF crystals; it is placed in cassettes with filters enabling the measurement of equivalent doses Hp (0.07) and Hp (10). For the assessment of the effective dose, this laboratory uses the model that certainly overestimates the value of effective dose in the routine analysis of dosimetry. Effective dose is equalized with equivalent dose Hp(10). In cases of exceeding the upper limit of the effective dose for category B (6 mSv/a), a series of significant parameters are considered for evaluation: usage of protective equipment, dosimeter position in relation to body and in relation to protective equipment (above/under the apron).

REPORT: The equivalent doses Hp (0.07) and Hp (10) are determined by analysis of personal dosimeter. Quotient of these two values depends on the energy by which dosimeter was irradiated. In that way, it is possible to identify the type of radiation source by using the present calibration. The values of characteristic peaks providing the assessment of timing of dosimeter irradiation are calculated by the glow curve deconvolution. This part of calculation is carried out according to present calibration for the group of analysed dosimeters of the same manufacturer and the same charge of dosimeter. The evaluation of timing of irradiation is not possible if the time between irradiation and read-out moment is over two months. Therefore, the policy of this laboratory is to stop the analysis of personal dosimeters in every three months.

CONCLUSION: It is necessary to cancel legal obligation for regular analysis of personal dosimeters for those working places where the possibility of irradiation of workers by doses significantly higher than doses generated by natural sources is negligibly low.