60Co γ-ray attenuation coefficient of barite concrete

ABSTRACT  Introduction: Recently uses of medium and high energy x-rays has been increased in Iran and radiotherapy centers along with a variety of accelerators have been installed in some provinces. In the other hand there is no sufficient skill in designing and making radiotherapy treatment rooms. This study was conducted to evaluate the efficacy of different mixtures of barite concrete for shielding the radiotherapy rooms. In this way we emphasized on determining the size and amount of barite aggregations to achieve the maximum radiation attenuation which leads to minimizing wall thickness in treatment room. Materials and Methods: To increase concrete density, the barite aggregation was added to concrete. Different size variations of barite aggregates mixed with different water/cement ratio were examined. The dimension of cubic concrete specimens for compression strength test was 15×15×15 cm. The rectangular barite concrete blocks with different compressions as used for strength test with cross section of 10×10 cm and thicknesses from 5 to 40 cm were used for radiation attenuation test. For this test concrete specimens were irradiated by gamma beam of 60Co (Phoenix Theratron). The transmission radiation through the blocks was measured by a Farmer ionization chamber (FC65P) in Yazd radiotherapy center. Results: Our findings showed that in all specimens the highest mean compression strength was related to the specimens with equal ratio of fine to coarse barite aggregates but the lowest HVL was obtained from mixtures with fine to coarse ratio of 35/65. The concrete sample with a 0.45 water/cement ratio, 350 kg/m3 cement and equal amounts of fine and coarse barite sands had nearly minimum half value layer(HVL) and maximum compression strength, so this sample was considered as the best barite concrete sample. Conclusion: Since HVL of the barite concrete specimens with the same compression strength is markedly lower than the conventional concrete and we have a plenty barite mines in our country it is recommended to use barite concrete with the best mixture condition based on our findings for shielding the radiotherapy rooms.