Kimura K, Ishikawa T, Kinno M, Yamadera A, Nakamura T
Technical Research Institute, Fujita Corporation, Yokohama, Japan.
Health Phys. 1994 Dec;67(6):621-31. doi: 10.1097/00004032-199412000-00005.
We measured the depth distribution of residual long-lived radioactivity in the inner concrete wall of a cyclotron vault by assaying concrete cores and we estimated the neutron flux distribution in the inner concrete wall by means of activation detectors. Nine long-lived radioactive nuclides (46Sc, 59Fe, 60Co, 65Zn, 134Cs, 152Eu, 154Eu, 22Na, and 54Mn) were identified from the gamma-ray spectra measured in the concrete samples. It was confirmed that the radionuclides induced by thermal neutrons through the (n, gamma) reaction are dominant, and that the induced activity by thermal neutrons is greatest at a depth of 5 to 10 cm rather than at the surface of the concrete and decreases exponentially beyond a depth of about 20 cm. By comparing the radioactivity and neutron flux distributions, we can estimate the induced long-lived radioactivity in concrete after a long period of operation from the short-term activation measurement.
我们通过分析混凝土芯样来测量回旋加速器地下室内部混凝土壁中残余长寿命放射性的深度分布，并借助活化探测器估计内部混凝土壁中的中子通量分布。从混凝土样品中测得的伽马射线能谱中识别出了9种长寿命放射性核素（46Sc、59Fe、60Co、65Zn、134Cs、152Eu、154Eu、22Na和54Mn）。已证实，通过（n，γ）反应由热中子诱发的放射性核素占主导，热中子诱发的活度在混凝土深度5至10厘米处最大，而非在混凝土表面，并且在超过约20厘米的深度后呈指数下降。通过比较放射性和中子通量分布，我们可以从短期活化测量中估算出长期运行后混凝土中诱发的长寿命放射性。
