3P-33（3B-O2-1620） PDF
236U AMSの開発及び福島周辺土壌中の236U濃度測定
Natural 236U (T1/2=2.342×107y) is produced by capturing of thermal neutron, whereas anthropogenic 236U is generated by artificial nuclear reaction and released into the environment by global fallout, spent fuel reprocessing, and nuclear power plant decommissioning. Isotopic ratio of contaminated soil and sea water, for instance, are estimated to be 236U/238U~10-9 while it is ~10-12 in natural, therefore the anthropogenic 236U is potential tracer in the environment.
There are mainly two targets for development of AMS in MALT (Micro Analysis Laboratory, Tandem accelerator). The first is natural samples: sea water, coral core, and soil. Isotopic ratio 236U/238U in these samples might be ~10-12. The second is the 236U assumed to have leaked from Fukushima nuclear power plant. The target isotopic ratio should be much higher than natural samples (236U/238U~10-9).
Aiming at the background level of less than 10-12, development of 236U AMS system had started at MALT. The background of 10-10 level being achieved, current target is soil samples around Fukushima. The chemical treatment for the soil sample is now examined. For the further improvement of the background, the beam orbit of main interference, 235U5+, is also analyzed.