DEVELOPMENT OF EXTREMELY LOW-LEVEL NEUTRON BY ACTIVATION METHOD AND ITS APPLICATION TO VARIOUS ENVIRONMENTS.

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(1)Anti-coincidence method by using Plastic Scintillation counter was applied to reduce background counts of the Ge detectors in Ogoya underground laboratory(OUL). Results obtained by fundamental research were presented at the International Conference of Low-Level Radioactivity Measurements Techniques(LLRMT) held 6n Oct.13-17, 2003 at Vienna, Austria.(2)Fundamental parameters for the measurement of low-level neutrons by activation technique were determined under the operation of small reactor of UTR, Kinki(1W).(3)Environmental neutron has been monitored at Rokkasho-mura, Aomori Pref. Results were reported at the International Conf.jel ; d at Maidstone, England Sep.19-26,2002 and published in "Environmental Radiochemical Analysis II".(4)Level of environmental neutron in sea water of the range of 0 to 4m was measured three times at Ogi marine Research Laboratory. Small maximum of thermal neutron flux was observed at 5-10cm depth, which agrees well with theoretical calculation.(5)Neutron flux has been monitored regularly at Tatsunokuchi(35m above sea level) and Shishiku Highland(640m).(6)Separation method of Eu and Ac was developed to detect extremely low-level Eu-152 produced by Atomic Bomb in 1945.(7)Eu-152 measurements of Hiroshima granite samples were reported for the publication of DS02 (Dosimetry System 2002 for the evaluation of radiation dose of Hiroshima and Nagasaki Atomic Bomb in 1945).(8)Results of Co-60 measurement in the spoons exposed to the JCO criticality accident were published in J.E.R.(9)Got prize from Radiation Effect Research Association for the contribution to extremely low-level neutron measurement by activation method.(Mar.2003).