Study of the utilization of the thermoluminescent dosemeters (T.L.D. 100, T.L.D. 600 and T.L.D. 700) in mixed fields, using a source of Am-Be and Monte Carlo code

The research and application of the phenomenon of the thermoluminescence have made considerable progress during the last two decades. Th e use in a large scale of the thermoluminescent in personal dosimetry, environmental monitoring, diagnostic radiology and radiotherapy, have resulted in the development of a great variety of thermoluminescent readers proper for routine tasks, some of them are commercially available. The most popular materials yield in laboratories are: LiF:Mg, Ti; LiF:Mg,P,Cu; CaF2: Mn; CaF2:Dy; CaSO4:Dy,Mn; Li2B4O7:Mn; Li2B4O7:Cu; MgB4O7:Dy. The T.L.D.-600 is a dosimeter sensible enough to thermal neutrons, as also to gamma radiation, while the T.D.L.-700 just practically shows answer to gamma radiation. So, in mixed field of radiation with thermal neutrons and gamma radiation, it must be used in dosimetry a pair of dosimeters: T.L.D.600 and T.L.D.-700 and both must be properly calibrated, by evaluating the dose of the thermal neutrons from the difference between the answers from the two dosimeters. This work aims to evaluate the behavior of the thermoluminescent detector, T.L.D.100, T.L.D.600 and T.L.D.-700, with neutrons. The study was carried out in two stages: in the first one there were an experimental evaluation using a neutron source of 241 Am-Be with and without moderation, the second stage was to carry out simulations of the experimental arrangements with Monte Carlo code (M.C.N.P.4.b), with the same spectrum of the 241 Am-Be source and the same moderation. Even tough the T.L.D. 600 can detect neutrons in the fast energy range (10 KeV - 10 MeV) its absorbed dose is very low, then it is not so efficient for dosimeter in this energy range. We could observe that the T.L.D.s 100 and 600 are efficient in the detection and in the dosimetry of thermal neutrons; the same thing can not be verified for the T.L.D. 700. The T.L.D. 600 has an answer dozens times larger than the T.L.D. 700 and 1,6 larger than T.L.D. 100 for neutrons in the thermal energy range. It could be observed that the T.L.D. 700 has practically the same answer for the detection of the neutrons of the T.L.D. 100, for neutrons with high energy, where the neutrons energy range was about 4,5 MeV. In the fact of the T.L.D.700 increases its efficiency in the detection of the neutrons, although very low, owing to scattering cross section of the Lithium 7 (T.L.D. 700), which increases together with the energy of the neutrons. With the Natural Lithium (T.L.D. 100) is different because it has its absorption cross section diminished with the increase of the energy of the neutrons. Even tough the T.L.D. 600 can detect neutrons in the fast energy range its absorbed dose is very low, then it is not reliable its efficiency in the dosimetry in neutrons. The same behavior was observed for the T.L.D.s 100 and 700. The experimental results confirm the simulated results; the resonance peaks were expected in the B.N.L. (Brookhaven National Laboratory); the T.L.D.s had efficiency as expected by the maker. (authors)