Effects of gamma rays on normal-high-density concrete

Abstract

Concrete is one structural and shielding material used against ionising radiation. It is used in radioactive environment such as radiotherapy rooms and radioactive safe keeping. Optimise concrete is evaluated by its thickness and also course and fine aggregate. Mixture of course and fine aggregate in concrete and its grade play an important role as good radiation absorber. However, concrete with unsuitable mixture will display cracks and will cause radiation leakage which could harm the public’s health. Therefore, this research is carried out using normal concrete with high density to determine the optimal grade. Four grades of concrete were produced, with mixture of cement, water and course-fine aggregate i.e. limestone and silica sand. Attenuation coefficient is measured using gamma spectrometer NaI (Tl) and single channel analyser (SCA). Radiation source used are Cs-137 and Co-60with photon energies of 0.662 MeV, 1.173 MeV and 1.332 MeV. Calculation of attenuation coefficient for concrete with thickness of 2.6 cm, 5.2 cm, 7.8 cm, 10.4 cm dan 13 cm shows increase in attenuation coefficient (<1.0 cm-1) for each grade, namely M15, M25, M35 dan M45. The result shows optimum concrete grade is M35 as the attenuation coefficient, which is between 0.04 - 0.18 cm-1, is the lowest in comparison with the other grades. Thus normal high density concrete could be used as effective shielding material and viable.