Evaluation of gamma radiation cumulative exposure monitoring system in the Nuclear Technology Development Center (CDTN) with thermoluminescent dosimeters

Cumulative exposure to gamma radiation is monitored at the Nuclear Technology Development Center - CDTN, located on the campus of the Federal University of Minas Gerais in Belo Horizonte - MG, since 1986. This monitoring is part of the Institution's Environmental Monitoring Program. The measurement is carried out through the use of thermoluminescent dosimeters (TLD's), which are placed in the perimeter of the CDTN property, distanced approximately 50 m each other, and at the air sampling stations, totaling 36 sampling points. The TLDs are positioned one meter from the ground, inside a PVC pipe where they remain exposed for a period of approximately three months. The objective of this work is to present and evaluate the results of this monitoring by investigating the dose values of gamma radiation (Dose Equivalent to Photons) obtained. Another important issue presented is about some failures identified in certain periods. There were problems with the sampling methodology and changes were proposed in the shelters to avoid contact of TLDs with excess moisture, which can compromise the results and the equipment of measurement of the thermoluminescence of crystals. The change was made at a sampling point and the results were compared with the historical data in the last 30 years. (author)