The fallout caused by the accident of Chernobyl' nuclear reactor has been monitored in Niigata City (April 30-June 3, 1986) . Twelve nuclides (131I, 132I, 129Te, 129mTe, 132Te, 134Cs, 136Cs, 137Cs, 103Ru, 99mTc, 140La, 140Ba) were identified in aerosol samples. The same nuclides plus7Be were identified in rain-water. Gaseous and particle-bound131I were separately trapped on a glass filter and a charcoal filter, respectively. Results indicate 50-60% of atmospheric131I is gaseous and the rest is particlebound. Chloroform extraction of rain-water revealed that 40-60% of131I in the rain-water sample exists in the form of IO3-and131IO3- (131IO4-) /131I-seemed to increase with the lapse of time after the accident.
The environmental radioactivity caused by the reactor accident at Chernobyl'was investigated from May 7 to May 31 of 1986 in Toyama. Measurement of radioactivities in airborne particles, rain water, drinking water, milk, and mugwort are carried out by gamma-ray spectrometry (pure Ge detector; ORTEC GMX-23195) . Ten different nuclides (103Ru, 106R, 131I, 132Te-I, 134Cs, 136Cs, 137Cs, 140Ba-La) are identified from samples of airborne particles. In the air samples, a maximum radioactivity concentration of each nuclide is observed on 13th May 1986. The time of the reactor shut-down and the flux of thermal neutron at the reactor were calculated from131I/132I and137Cs/134Cs ratio. The exposure dose in Toyama by this accident is given as follows: internal exposure; [thyroid] adult-59 μSv, child-140 μSv, baby-130 μSv, [total body] adult-0.2 μSv, child, baby-0.4μSv, external exposure; 7 μSv, effective dose equivalent; adult-9μSv, child-12 μSv, baby-11 μSv.
A simplified monitoring method of125I in liquid waste was devised. The waste water of 200 cm3was taken on a Saran (polyvinylidene chloride) film covering a stainless steel vat.A stable iodine (20 mg) and sodium hydroxide (1 mmol) was added. The water was evaporated using an infra-red lamp. After heating to dryness, the Saran film was folded and transferred into a polyethylene tube. The radioactivity of125I was counted with a well type NaI (Tl) scintillation counter. When a multi-channel analyzer was available for counting, an absolute decay rate of125I was calculated with single and sum photo-peak counts. The radioactivity of125I counted by a single-channel counter must be corrected with the counting efficiency of about 55 %, with a special emphasis of a self absorption of photons. The recovery of125I for concentrations below the permissible level was more than 98%.