Some Japanese old porcelain samples, manufactured after middle of Edo-era (approximately 1600 AD), were initially investigated using thermoluminescence phenomena. Disc samples 9.4 mm in diameter and 1 mm thickness), prepared from the porcelain samples, were subjected to the thermoluminescence colour imaging (TLCIs) after artificial radiationexposure. Almost all porcelains showed red-TLCIs, giving homogeneous distribution except a few granular red patterns in the oldest porcelains, while the all earthenwares resulted in the granular patterns due to both blue and red grains as remaining minerals after burning On the basis of TLCIs results, the RTL-chronological method was applied using the porcelain discs and a highly sensitive RTL-measuring apparatus, which was installed with a light pipe (10 mm core-rod type glass) and a biotite light shielding plate to eliminate the black radiation. Naturally accumulated RTL, rendering extremely faint intensity, has been quantitatively determined and both regeneration and additive dose techniques were applied. As a result, some RTL-ages, concordant with the estimated ones, were obtained, resulting in possibility enable to estimate very young ages up to 30 years for porcelain samples and dose-evaluation of nuclear-energy related accident using ceramics materials.
The trapping energy level (E) from conduction band is well known to be intimately correlated with the mean lives (τ) of captured electrons and holes in quartz grains, resulting in the applicable criterion of thermoluminescence (TL) dating using a coarse grain method. The experimental evaluation of accurate E-values has been carried out using an initial rise method combined with radioluminscence (RL) measurements for the correction of thermal quenching effects at higher temperature. The naturally accumulated red-TL (RTL) and blue-TL (BTL) grains from quartz grains from a dune sand were subjected to the present method. As a result, the correction of the thermal quenching effects always brought the higher E-values in the range of 0.1 to 0.25eVin comparison with the low activation energies from initial rise method of glowcurve analysis alone. It was again confirmed that the E-value of RTL gives higher than that of BTL in natural quartz grains. Consequently, the finally evaluated mean lives of RTL were certainly longer than those of BTL. This result supports that the RTL-dating is more preferable for the age-determination beyond 500 ka because of high stability of RTL. The E-values were also compared with the results from the isothermal analysis of TL-glowcurves.
To determine the recently accumulated state of the radiocesium137Csin surface sediment in the brackish-water Lake Obuchi, surrounded by facilities reprocessing spent nuclear fuel in Rokkasho Village, we investigated concentration of137Csin the sediment and speciation of137Csin the sediment according to standard procedures of sequential extraction. Concentrations of137Csin the sediment, the silty types (8.0 -13.8Bq kg-1dry) were higher than the sandy type (0.2Bq kg-1dry) . Concentrations of137Csin the sediment tended to be higher in the smaller particle sizes. Moreover, we observed a high correlation coefficient between137Csconcentration in the sediment and amount of organic matter. We found that most137Csin the sediment were the speciations (contained within the crystal structures of minerals etc.) that non-eluted under a natural condition; however, the137Csbonded to organic matter in the sediment were only about 5 % of the sum total of each extraction. This suggests that organic matter acts as a carrier in137Csaccumulation on the lake bottom. Also, 137Csin the sediment can more readily exist in a stable state when bonded to minerals, possessing a crystal structure, rather than to organic matter.
Gamma-ray spectrometry with germanium detectors has been frequently applied for monitoring radioactive materials in sites of nuclear facilities. When cascade gamma-rays simultaneously interact with the detector, spurious peaks, so-called coincidence-sum peaks, and the full energy peaks with reduced intensity are observed in an apparent pulse height spectrum. Although there are some reports on the correction of the coincidence-sum effect, most of them cannot be easily applied for routine measurements. In order to make the correction simple, the method with the experimental formula of peak-to-total ratio given by the authors is presented. The intensities of full energy peaks corrected by the present method show good agreement with those by the method using total detection efficiencies.