Development of a Dosimeter for High Doses Assessment Based on Alanine/EPR

INTRODUCTION The increasing use of radiation sources of high activity for industrial and medical applications and in the generation of electric energy and the consequent increase in the probability of to occur accidents, becomes important the research and the development of detectors and dosimetry methods for quality control of the applied doses. The radiation dosimetry is important for all radiation processes, it has as objective the determination of the absorbed dose resulting from the interactions of the ionising radiation with the medium, decisive condition to the effectiveness of the dosimeter (1). The electron paramagnetic resonance (EPR), also well-known as electron spin resonance (ESR), is a technique commonly used for high doses dosimetry of the gamma, X, neutron and electron radiations, accident dosimetry, archaeological and geological dating, studies of defects, characterization of materials, analysis of radicals, etc. The EPR technique detects unpaired electrons trapped in the crystalline lattice. The trapped electrons are measured by microwaves absorption spectroscopy, and the intensity of the EPR signal is proportional to the absorbed dose. The non destructive nature of the EPR detection also allows the study of species trapped in biological samples such as bone, quartz, tissues, drug, teeth, hair, fingernails and dry skin. The most used inorganic materials are: MgO:Mn, stalactites, stalagmites, chorales, shells, bones, minerals, Al2O3:Cr(ruby), and the organic ones are the amino acids (alanine) and sugars (2,3,4). Some advantages of EPR are: the information is cumulative with the dose, the reading is not destructive, high sensibility, handle easiness, good reproducibility, small fading of the sign, large linearity interval, doesn't present energy dependence and it allows the use of organic materials, once the measurement is made at room temperature or at the liquid nitrogen temperature. The main disadvantages are the high cost of the EPR equipment and the fact that organic materials could not be reused, once they cannot suffer thermal treatment at high temperatures. The use of the alanine as a dosimeter happened after the discovery of EPR technique. The alanine presents a very resolved spectrum and a great number of free radicals formed by absorbed dose unit, it is an amino acid with effective atomic number very close of the human tissue, it presents a stable and simple signal, with low background, low cost, easy handling and available universally (5,6,7,8). The dosimetric system using alanine as detector element can be considered a reliable system for absorbed dose measurements in processes of industrial irradiation. They are also being studied and applied in medical irradiation processes, where lower doses are used (9,10,11,12,13).