10MV医療用直線加速器からの漏洩放射線について : 第2報加速器ヘッド部分からの中性子漏洩と治療室内中性子線量当量およびフルエンス分布

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Neutron measurements for Mitsubishi ML-15M II B Medical linac operated in the 10 MV photon mode were carried out at different locations in a treatment room by an idone activation method with two Bonner spheres (11.5 cmφ, 20 cmφ). The method was established by Yamaguchi et. al. and can determine neutron fluence and flluence to dose equivalent conversion factor. The measurement of ^<128>I activity through ^<127>I (n, γ) ^<128>I reactions in iodoform detectors were taken after exposing each iodoform detector with or without the use of a cadmium filter (1.00 mm thick) in bare or in each of the Bonner spheres, and the results were used for determing the neutron fluence and the fluence to dose equivalent conversion factor. It also contains a method for estimating average energy of neutrons. 1. Major neutron sources considered within a treatment head are : Pt-target ; main collimator & the parts around it ; flattening filter and movable jaws in the case of 0×0 cm^2 field. Estimated relative yields for each of the above sources were 55,26,5 and 14% to total yield respectively. 2. Total leakage neutron source strength was found to be 6.4×10^<11> and 2.9×10^<11> neutrons/Gy of X-ray in the case of using Pt-target and Cu-target respectively. 3. Estimated average neutron energy was 0.43 MeV at a lacation near the front surface of the treatment head, and 0.36 MeV at the isocenter for 0×0 cm^2 field. The average energies at other locations in the room were also estimated. 4. The distribution of neutron dose equivalent in the room was approximately inversely proportional to the square of the distance from the target. At the isocenter, percent neutron dose equivalent per unit X-ray output was 0.2 and 0.06 %Sv/Gy of X-ray for 30×30 cm^2 (fully opened) and 0×0 cm^2 field respectively.
公益社団法人日本放射線技術学会の論文
1983-01-01

10MV医療用直線加速器からの漏洩放射線について : 第2報加速器ヘッド部分からの中性子漏洩と治療室内中性子線量当量およびフルエンス分布

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10MV医療用直線加速器からの漏洩放射線について : 第2報 加速器ヘッド部分からの中性子漏洩と治療室内中性子線量当量およびフルエンス分布

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10MV医療用直線加速器からの漏洩放射線について : 第2報加速器ヘッド部分からの中性子漏洩と治療室内中性子線量当量およびフルエンス分布