Calculation of Calibration Coefficients of Ionization Chambers

Abstract

Radiation dosimetry measurement is very important issue in radiation protection to determine the harmful level of radiation. To measure radiation we need specific devices with special properties i.e. Dosimeters. To ensure the accuracy and precision of these dosimeters a calibration must be performed to dosimeters and beams. In this study calibration coefficients were provided to three ionization chambers two of them spherical type and the other one farmer type, by using the spherical ionization chamber as a reference dosimeter. All measurements were done at secondary standard dosimetery lab in Sudan , the gamma irradiator OB-85 was used to exposed the all chambers reference and under calibration, the reference ion chamber was exposed at five meters distance and ten readings were taken with calculation average in every meter, the readings were obtained in charge mode because the experiments were don in protection level and convert the readings to air kerma, the other three chambers were exposed as the reference chamber with similar calculation. The results showed that , row readings {(5.28 ± 7.30)nc/m , (2.71 ± 3.79)nc/m , (5.28 ± 7.32)nc/m , (0.06 ± 0.04)nc/m},air kerma {(143.82 ± 198.71)µGy , (73.30 ± 102.30)µGy , (143.81 ± 199.28)µGy , (1.66 ± 1.05)µGy}, calibration coefficient {(25±0.00)µGy/nc , (49.96 ± 0.94)µGy/nc , (25.05 ± 0.12)µGy/nc , (4.25 ± 1.23)µGy/nc} as average with stander deviation for reference chamber, farmer, spherical and spherical 30 〖cm〗^3chamber respectively. The variation in result refer to chamber properties, from this study after providing the calibration coefficient we found that each chamber has identify calibration coefficient and the reading of chamber depend on chamber shape and sensitive volume and the chambers can have more than one calibration coefficient . The study was done in limited range of energy Cs-137, recommend to do more studs at wide range of energy to see what the variation.