140 keV 감마선 차폐 시 납 차폐체 두께에 따른 깊이별 선량 평가

Abstract

The present study made a phantom for gamma ray of 140 keV radiated from 99mTc, examined shielding effect of lead by thickness of the shielding material, and measured surface dose and depth dose by body depth. The OSL Nano Dot dosimeter was inserted at 0, 3, 15, 40, 90, and 180㎜ depths of the phantom, and when there was no shield, 0.2㎜ lead shield, 0.5㎜ lead shield, The depth dose was measured. Experimental results show that the total cumulative dose of dosimeters with depth is highest at 366.24 uSv without shield and lowest at 94.12 uSv with 0.5㎜ lead shield. The shielding effect of 0.2㎜ lead shielding was about 30.18% and the shielding effect of 0.5㎜ lead shielding was 74.30%, when the total sum of the accumulated doses of radiation dosimeter was 100%. The phantom depth and depth dose measurements showed the highest values at 0㎜ depth for all three experiments and the dose decreases as the depth increases. This study proved that the thicker a shielding material, the highest its shielding effect is against gamma ray of 140 keV. However, it was known that shielding material can't completely shield a body from gamma ray; it reached deep part of a human body. Aside from the International Commission on Radiation Units and Measurements (ICRU) recommending depth dose by 10㎜ in thickness, a plan is necessary for employees working in department of nuclear medicine where they deal with gamma ray, which is highly penetrable, to measure depth dose by body depth, which can help them manage exposed dose properly.