第4章患者救済に奔走した活動記録〈論文・研究発表〉FUKUSHIMA いのちの最前線501 For the Fukushima Daiichi Nuclear Power plant, we have to wait until inspections reveal details of radioactive nuclides emitted in the accident. In Chernobyl, one of the dominantly emitted radioactive nuclides was assumed to be harmless xenon 131. Some of the other nuclides have short half-life such as that of iodine-131 of which is eight days and tellurium-132, which turns into iodine-132 within a very short period of time. Radioactive cesium which has a relatively long half-life was also thought to be included1) (Table 1). Since iodine 131 and radioactive cesium were the dominantly emitted substances in Chernobyl, it is thought that this is the similar case in Fukushima. However, whereas only trace quantities of radioactive strontium and plutonium, which led to safety concerns regarding MOX fuel, were found outside the Fukushima nuclear plants, a significant amount of those radioactive materials was released in Chernobyl. The emitted amount (approx. 520 TBq) in Chernobyl was approximately seven times more than that in Fukushima as of today even though these two accidents are in the level 7 of INES. Among the substances mentioned, radioiodine, especially iodine-131 is thought to be the one which most affected people's health around Chernobyl. Iodine 131 accumulated in thyroid glands particularly through food intake and resulted in internal exposure. Infants in Chernobyl also suffered internal exposure due to the intake of milk containing high density of iodine-131. Because the Soviet Union then did not control either food distribution or intake, people were unaware of ingesting contaminated milk, vegetables, water, etc. This was considered to be the main reason of internal exposure2). The most dominant nuclide emitted during the accident at the Fukushima Nuclear Power Plant was iodine-131. Another major component of the emissions was radioactive EMITTED RADIOACTIVE NUCLIDES AND COUNTERMEASURES FOR INTERNAL EXPOSURETable 1. Radionuclide emitted in the accident at the Chernobyl Nuclear Power Plant (Modified the data in Reference 1)RadionuclideHalf-lifeRadiationEmission amount (PBq)*Neptunium 23958 hrsβ-rays, γ-rays95molybdenum 9967 hrsβ-rays, γ-rays>168tellurium 13278 hrsβ-rays, y-nys1,150xenon 1335 daysβ-rays, γ-rays6,500iodine 1318 daysβ-rays, γ-rays1,760barium 14013 daysβ-nys, γ-rays240cerium 14133 daysβ-ays, γ-rays196ruthenium 10340 daysβ-rays, γ-rays>168strontium 8952 daysβ-rayszirconium 9565 daysβ-nys, γ-rays196curium242163 daysα-rayscerium 144285 daysβ-rays, γ-rays116ruthenium 1061 yearβ-rays, γ-rays>73cesium 1342 yearsβ-raysplutonium 24113 yearsβ-raysstrontium 9028 yearsβ-rayscesium 13730 yearsβ-rays, γ-rays85plutonium 23886 yearsα-raysplutonium 2406, 850 yearsα-rays, γ-rays0.042plutonium 23924,400 yearsα-rays, γ-rays0.030 *PBq is equivalent to 1015 becquerel.