Authors:H. Oda, T. Masuda, E. Niu, and T. Nakamura
Radiocarbon ages of 17 ancient Japanese documents of known age and 3 unknown samples were measured by AMS. Radiocarbon dating on the known documents concluded that the Japanese paper is a suitable sample for radiocarbon dating because of small discrepancy between the calibrated radiocarbon age and the historical age due to the characteristics of Japanese paper. From the dating of the paper samples of unknown age, the wood-block prints, it was clarified that they had been produced between the 11th century and the first half of the 12th century as the historical information suggested.
Authors:Y. Ishikawa, N. Sato, E. Nakamura, T. Sekine, and K. Yoshihara
Accumulation of radiosilver108mAg and110mAg in oysters (Crassostrea gigas) and their behavior in marine environments has been studied in the northeast Pacific coast in Japan. Enrichment of radiosilver in oysters depends on topographical conditions; significant bioaccumulation occurred in open bays, while it was hardly observed in bays with narrow shaped entrances. From these observations difference of the behavior of radiosilver between open and nearly closed bays is suggested.110mAg in oysters decayed with an effective halflife of about 150 days for both the Chinese nuclear weapon test and the Chernobyl accident. In contrast to radiosilver, the fission product nuclide137Cs was almost independent of topographical conditions, and its concentration was constant.110mAg bioaccumulation in oysters after the Chernobyl accident in 1986 was found in both open and nearly closed bays, the latter showing much lower concentration of radiosilver than the former. Specific activity of108mAg in oysters was determined in bays open to the Pacific Oceans.
Authors:T. Nakamura, S. Kojima, T. Ohta, M. Nishida, A. Rakowski, A. Ikeda, H. Oda, and E. Niu
14C variations of atmospheric CO2 as well as carbonaceous fraction of living materials, such as collagen from tooth and bone, tissue, skin, hair, nail, etc.,
of modern humans are influenced by 14C produced artificially by nuclear bomb tests in the atmosphere from late 1950s to early 1960s. By careful investigation of
14C concentration of tree rings and human body samples formed in this time intervals, we can establish a relationship of their
14C concentrations with calendar year. By applying this relation to a sample whose 14C concentration can be measured, we can estimate the formation age of the sample. In addition, sources of the chemicals that
were used in some criminal cases can be possibly identified, by their carbon isotope ratios (13C/12C and 14C/12C). This method of age determination has been applied to a forensic study, i.e., two criminal cases of murder. For each case,
by comparing the measured 14C abundances of several pieces of hair and one tooth (the third molar) from the body with the annual change on concentrations
of bomb-produced 14C, the time of death of the body and the age of the victim were estimated. The estimated values were consistent with the real
ones that were revealed by the confession of the real murderers.