Cyclotrons used in nuclear medicine imaging accelerate protons, deuterons, and helium ions to bombard a target, which produces nuclear reactions that generate positron-emitting radionuclides. Secondary neutrons are nonuniformly emitted in these reactions and induce heterogeneous activation of the cyclotron components and concrete vault enclosure. This poses radioactive waste management complications when decommissioning a cyclotron facility, since the objective is to ensure that exposures are within regulatory limits and as low as reasonably achievable (ALARA). The McGovern Medical School in The University of Texas Health Science Center in Houston housed a Scanditronix MC40 cyclotron that produced short-lived radioisotopes for Positron Emission Tomography (PET) imaging from 1984 to 2001 until Tropical Storm Allison rendered it inoperable. The purpose of this study was to provide underrepresented Science, Technology, Engineering and Mathematics (STEM) students an ALARA experience with a practical problem encountered in the radiation safety profession. Gamma dose rate measurements were performed with both a Mirion InSpector 1000 spectrometer and Fluke 451P survey meter in the vault at locations identified as hotspots based on preliminary scoping surveys with the Ludlum model 44-9 detector. However, gamma spectra were measured with the spectrometer exclusively at hotspots along the west wall. Results indicated the maximum gamma dose rate of 129 ± 31 nSv h was about 2 times background near the central beam transport line of the now inoperable cyclotron. Furthermore, gamma emission peaks were identified in the spectra from trace amounts of Co and Eu in the vault's concrete walls.

中文翻译：

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由辐射安全专业中代表性不足的学生学员进行的回旋加速器退役放射评估练习。

核医学成像中使用的回旋加速器加速质子、氘核和氦离子轰击目标，产生核反应，产生正电子发射放射性核素。二次中子在这些反应中不均匀地发射，并引起回旋加速器部件和混凝土拱顶外壳的异质激活。这会在回旋加速器设施退役时造成放射性废物管理的复杂化，因为目标是确保暴露在监管限制内并尽可能低地合理实现（ALARA）。休斯顿德克萨斯大学健康科学中心的麦戈文医学院拥有一台 Scanditronix MC40 回旋加速器，该回旋加速器从 1984 年到 2001 年生产用于正电子发射断层扫描 (PET) 成像的短寿命放射性同位素，直到热带风暴艾里森使其无法运行。本研究的目的是为代表性不足的科学、技术、工程和数学 (STEM) 学生提供 ALARA 体验，以解决辐射安全专业中遇到的实际问题。使用 Mirion InSpector 1000 光谱仪和 Fluke 451P 测量仪在金库中对根据 Ludlum 44-9 型探测器进行的初步范围调查确定为热点的位置进行伽马剂量率测量。然而，伽玛光谱仅在西墙的热点处用光谱仪测量。结果表明，129 ± 31 nSv h 的最大伽马剂量率约为现已无法运行的回旋加速器中心光束传输线附近背景的 2 倍。此外，在金库混凝土墙中痕量的 Co 和 Eu 的光谱中发现了伽马发射峰。