Fujibuchi Toshioh, Nohtomi Akihiro, Baba Shingo, Sasaki Masayuki, Komiya Isao, Umedzu Yoshiyuki, Honda Hiroshi
Medical Quantum Science, Department of Health Sciences, Faculty of Medical Sciences, Kyushu University Graduate School of Medical Sciences, 3-1-1 Maidashi, Higashi-ku, Fukuoka, 812-8582, Japan,
Ann Nucl Med. 2015 Jan;29(1):84-90. doi: 10.1007/s12149-014-0918-6. Epub 2014 Oct 14.
Compact medical cyclotrons have been set up to generate the nuclides necessary for positron emission tomography. In accelerator facilities, neutrons activate the concrete used to construct the vault room; this activation increases with the use of an accelerator. The activation causes a substantial radioactive waste management problem when facilities are decommissioned. In the present study, several concrete cores from the walls, ceiling and floor of a compact medical cyclotron vault room were samples 2 years after the termination of operations, and the radioactivity concentrations of radionuclides were estimated.
Cylindrical concrete cores 5 cm in diameter and 10 cm in length were bored from the concrete wall, ceiling and floor. Core boring was performed at 18 points. The gamma-ray spectrum of each sample was measured using a high-purity germanium detector. The degree of activation of the concrete in the cyclotron vault room was analyzed, and the range and tendency toward activation in the vault room were examined.
(60)Co and (152)Eu were identified by gamma-ray spectrometry of the concrete samples. (152)Eu and (60)Co are produced principally from the stable isotopes of europium and cobalt by neutron capture reactions. The radioactivity concentration did not vary much between the surface of the concrete and at a depth of 10 cm. Although the radioactivity concentration near the target was higher than the clearance level for radioactive waste indicated in IAEA RS-G-1.7, the mean radioactivity concentration in the walls and floor was lower than the clearance level.
The radioactivity concentration of the inner concrete wall of the medical cyclotron vault room was not uniform. The areas exceeding the clearance level were in the vicinity of the target, but most of the building did not exceed the clearance levels.
紧凑型医用回旋加速器已被用于产生正电子发射断层扫描所需的核素。在加速器设施中，中子会使用于建造屏蔽室的混凝土活化；随着加速器的使用，这种活化会增加。当设施退役时，这种活化会导致严重的放射性废物管理问题。在本研究中，在紧凑型医用回旋加速器屏蔽室的墙壁、天花板和地板上钻取了几个混凝土芯样，这些芯样是在运行终止2年后采集的，并对放射性核素的放射性浓度进行了估算。
从混凝土墙壁、天花板和地板上钻取直径5厘米、长度10厘米的圆柱形混凝土芯样。在18个点进行取芯。使用高纯锗探测器测量每个样品的γ射线能谱。分析了回旋加速器屏蔽室中混凝土的活化程度，并研究了屏蔽室内活化的范围和趋势。
通过对混凝土样品的γ射线能谱分析鉴定出了（60）Co和（152）Eu。（152）Eu和（60）Co主要是通过中子俘获反应由铕和钴的稳定同位素产生的。混凝土表面和10厘米深处的放射性浓度变化不大。虽然靶附近的放射性浓度高于国际原子能机构RS-G-1.7中规定的放射性废物清除水平，但墙壁和地板中的平均放射性浓度低于清除水平。
医用回旋加速器屏蔽室内壁混凝土的放射性浓度不均匀。超过清除水平的区域在靶附近，但建筑物的大部分区域未超过清除水平。
