Development of an irradiation system of low-energy protons - To study the mechanism of the effects of neutrons for biological system-

中子的相对生物学效力比伽马射线和伽马射线高得多。作为中子暴露的案例，我们有广岛和长崎原子弹爆炸幸存者的经历，以及东海村事故。中子进入人体后会反冲氢原子中的质子，氢原子是主要成分。这种反冲质子带电荷。因此，它们产生自由基，诱导DNA双链断裂。这类质子反冲在中子剂量中的比例为70-80%，这取决于中子的能量。几乎所有这些损害都会得到修复；然而，其中一些是无法修复的，由此产生的损害被认为会导致癌症。最近，一些科学家提出，许多这样的损伤是在附近产生的，在这种情况下，DNA的损伤变得非常大，很有可能无法修复。这被称为“集群模型”。在另一种情况下，中子发生核反应并产生更多的放射性。它们发射粒子、伽马射线和中子。本研究的目的是利用洋葱根尖细胞辐照质子来发现中子的这部分辐射效应。质子是由广岛大学辐射生物学和医学研究所的申克尔型静电加速器产生的。辐照系统已完成，但辐照强度和辐照均匀性的调整尚未完成。因此，我们不仅用洋葱根尖细胞，而且用洋葱种子本身进行了中子辐照实验。辐照后的种子孵育，观察根尖细胞微核。利用中子发生器中0.2MeV、0.5MeV、0.8MeV和1.0MeV的单能中子和Cf-252中2.1MeV的平均能量，观察了根顶细胞的微核。干种子辐照的中子RBE值分别为216、186、180、174和150，萌发细胞辐照的中子RBE值分别为45.3、39.1、36.0、31.4和18。少

Relative biological effectiveness of neutrons is much higher than gamma- and beta-rays. As such cases of neutron exposure, we have experiences of atomic bomb survivors in Hiroshima and Nagasaki, and Tokai-mura accident. Neutrons when coming into human body recoil protons in hydrogen atoms which are included as a main component. Such recoil protons have charges. Therefore, as a consequence, they produce radicals, which induce DNA double strand breaks. The percentage of such proton recoils in neutron dose is 70-80% which depends on neutron energies. Almost all of such damages will be repaired; however, some of them will not be fixed, by which damages it is thought to induce cancers consequently. Recently some of the scientists proposed mat many of such damages are produced near by and that in such cases damages of DNA are become very large, which have large possibility not to be repaired. This is called as "cluster model". As the other case, neutrons have nuclear reaction and produces ra … More dioactivity. They emit particles, gamma rays and neutrons. The purpose of this study is to irradiate protons to find this part of radiation effects of neutrons using onion root top cells. Protons were produced by the Shenkel type electrostatic accelerator at Research Institute for Radiation Biology and Medicine, Hiroshima University. The irradiation system have been finished however adjustment for intensity and uniformity have not been done. Therefore we performed neutron irradiation experiment using not only onion root top cells but seeds themselves. After the irradiation seeds, they are incubated and micronucleus of the root tip cells are observed. We observed micronucleus of the root top cells by using monoenergetic neutrons of 0.2MeV, 0.5MeV, 0.8MeV and 1.0MeV from the neutron generator and average energy of 2.1MeV neutrons in Cf-252. The results of neutron RBE values are 216, 186, 180, 174 and 150 for dry seed irradiation, and 45.3, 39.1, 36.0, 31.4 and 18 for germination cells, respectively. Less