NaCl pellets for improved dosimetry

Sammanfattning: There is always a need to improve and develop new ways of estimating effective doses to people and environments that have been exposed to ionizing radiation. Dose monitoring is also important in hospitals and the nuclear industry. Today there are several commercially available dosimeters, the most common being thermoluminescent dosimeters, TLDs, made from LiF. These are widely used for personal dose assessment in hospitals and in the nuclear industry but the LiF is expensive and the calibration is time consuming. Access to TLD’s is usually limited and it would be desirable to develop a dosimeter that is readily accessible, easy to handle and cost effective on a large scale. Salt has been shown to be sensitive to ionizing radiation and has been used in retrospective dosimetry. Because of the dosimetric properties of salt it has been investigated in this project if commercially available salt could also be used as a passive, prospective dosimeter. If this is possible the applications could include dose optimizations in hospitals, dose assessments after radiological or nuclear, RN, incidents, dose mapping of contaminated areas and dose estimations on an individual scale for people unintentionally exposed to ionizing radiation. The aims of this project have been to find the optimal configuration for salt when pressed to the form of a pellet. Further, the dosimetric properties of the NaCl pellets, produced using six kinds of salt, have been investigated and a prototype dosimeter holder with appropriate energy compensation filters have been suggested. This project has shown that NaCl pellets are best when produced using salt grain sizes between 100-400 μm and a compression force of 3.0±0.5 tons. Further, the readout protocol used to obtain the OSL signal, which has been used for many previous measurements on salt, has been altered in this project because it was found that heating the NaCl pellets changes the sensitivity. In the new readout protocol, there is no heating of the NaCl pellets. The results also show that salt in the form of NaCl pellets have a linear dose response up to at least 6 Gy and that doses can be estimated using only one calibration, of the same size as the unknown dose, up to 100 mGy. For larger doses, >100 mGy, there is a sensitization of the pellets after exposure which complicates the dose estimations. The OLS signal show an inverse fading of about 20% after about 14 days when using the new readout protocol and the signal fading needs to be further investigated to obtain reliable results. Because of the low background signal in the NaCl pellets the MDD is very low, around 4-6 μGy, and it is possible to calculate an absorbed dose from the natural background after only three days. The conclusions of this project are that stable NaCl pellets can easily be produced and they have dosimetric properties which are suitable for dosimetry. With the appropriate energy compensation filters the NaCl pellets could be used as simple and accessible dosimeters in both hospitals, the nuclear industry and for individual dose assessments.