3D CAD BASED MONTE CARLO SIMULATION TO ESTIMATE SHIELDING EFFECTIVENESS OF AN IRRADIATION UNIT WITH ISO s-137Cs SEALED SOURCES AND INVESTIGATION OF DOSE HOMOGENEITY ON RADIOMETRIC BENCH AND ITS EXPERIMENTAL VALIDATION

---

Tezin Türü: Yüksek Lisans

Tezin Yürütüldüğü Kurum: Ankara Üniversitesi, Nükleer Bilimler Enstitüsü, Medikal Fizik Bölümü, Türkiye

Tezin Onay Tarihi: 2025

Tezin Dili: İngilizce

Öğrenci: AHMAT HARINE ABOUBAKAR

Asıl Danışman (Eş Danışmanlı Tezler İçin): Haluk Yücel

Eş Danışman: Serap Safran

Özet:

Gamma irradiation units are increasingly used in scientific, medical, and industrial fields to deliver effective radiation dose to samples and control of dose homogeneity, as well as carrying out radiological dose calibration of the instruments with desired accuracy and precision. The aim of this thesis is to measure and assess both the radiation shielding effectiveness and dose homogeneity on a radiometric bench when a gamma irradiation unit uses ISO s-¹³⁷Cs sealed sources, which are available at the Institute of Nuclear Sciences at Ankara University. The irradiation unit complying with ISO 4037-1 standard, manufactured by Hopewell Designs Inc., contains two sealed ¹³⁷Cs sources having nominal activities of 8.58 Ci and 50 mCi as of 14.05.2009. The dose measurements were performed on the radiometric bench and in a concrete shielding room. Then, a detailed 3D CAD model of the irradiation unit was developed considering technical diagrams of the unit, the radiometric bench and the shielded room. A licensed RayXpertâ Monte Carlo simulation software was used with this model to estimate dose distributions and shielding performance near the source and within the concrete shielded room. To validate the dosimetric results, dose homogeneity was studied at different distances of 50 cm, 100 cm, 150 cm and 200 cm, respectively, in a 30×30 cm² gamma-ray field area on the radiometric bench by using a PTW 30 cm³ ion chamber. It is found that dose homogeneity is better than 98% on a 30 cm x 30 cm gamma-ray field. In addition, the ambient dose measurements were conducted using both a 450 cm³ ion chamber and a Geiger-Müller detector. For the study of radiation dose homogeneity, the experimental and Monte Carlo simulated results in units of air-kerma values were used to evaluate the dose distribution at several x-y positions. The details of the findings are discussed in the thesis.