Yoshikazu Kikawada

Experimental Studies on the Mobility of Lanthanides Accompanying Alteration of Andesite by Acidic Hot Spring Water

Abstract The mobility of lanthanides (Lns) accompanying interactions of powdered andesitic rocks with acidic hot spring water and acidic hot spring water vapor/steam was studied in the experiments set up in the field. At the early stage of rock alteration, light Lns were slightly easier to be leached out by acidic hot spring waters from andesitic rocks than heavy Lns. This result qualitatively agreed with the result obtained in the previous experiments carried out in the laboratory. It was also found that the Ln abundance patterns (Ln patterns) obtained by normalization with Ln contents of the original rock showed slightly positive Eu anomalies at the early stage of rock alteration and turned to show negative Eu anomalies and the extent of negative anomaly monotonously increased as rock alteration proceeded. This trend in the direction of Eu anomaly was correlated to the degrees of decompositions of major rock-forming minerals and interstitial materials in the rock. At the earliest stage of rock alteration in acidic environments, the interstitial materials with relatively low Eu contents were decomposed, which resulted in the positive Eu anomaly. In the following stage, feldspar that had a relatively high Eu content was decomposed, which led to the negative Eu anomaly.

Determination of the lanthanoids in a neutral hot spring water by neutron activation analysis

Determination of the lanthanoids in a neutral hot spring water has been studied by menas of neutron activation analysis. The aluminium coprecipitation process, which used aluminium as the collector of the lanthanoids, was incorporated in the preparation of a sample for irradiation. Nine lanthanoids, La, Ce, Nd, Sm, Eu, Tb, Tm, Yb and Lu, were determined at ppt levels with satisfactory precision, indicating the effectiveness of aluminium coprecipitation.

210Pb deposition in the far East Asia: Controlling factors of its spatial and temporal variations

In order to better understand the behavior of (210)Pb deposition in Far East Asia, comprehensive data of monthly (210)Pb deposition, which includes several time-series and spatial distribution data at 14 stations in Japan and 2 stations in Taiwan, were analyzed. Pb-210 deposition at most of the sites exhibited a typical seasonal change with higher values in winter and lower values in summer; especially, the greatest (210)Pb deposition in the world occurred in winter at sites beside the Japan Sea. The deposition behavior of (210)Pb in Far East Asia differed between winter and summer. The meteorological phenomenon peculiar to winter of the Japan Sea side, i.e., formation of the Japan Sea convergence zone, might cause the high (210)Pb concentration in rainwater, as may heavy snowfall. The (210)Pb concentration in rainwater showed long-term variability, although this differed between winter and summer. This long-term variability may be related to climatological factors such as El Niño.

Anomalous Uranium Isotope Ratio in Atmospheric Deposits in Japan

The ratio that is different from the natural ratio is thusconsidered to originate from anthropogenic nuclear activitiesexcept for natural nuclear reactors. In the 1950s, JapanMeteorological Agency (JMA) started the sampling of atmo-spheric deposits in Japan and the measurement of anthropo-genic radioactivity for the monitoring of environmental pol-lution connected to nuclear activities.

ABUNDANCE OF LANTHANOIDS IN ROCK SALTS DETERMINED BY NEUTRON ACTIVATION ANALYSIS

Contents of lanthanoids (Lns) of rock salts have been measured by neutron activation analysis. Original salt samples were treated in advance of neutron irradiation so that Lns were enriched and amounts of interfering nuclides were reduced. The contents of Lns were at ppt-sub ppb levels and were comparable with or slightly lower than those of solar salts. The Ln abundance patterns of the salts were those with relative depletion in the heavy Lns, thus having negative slopes. It was indicated that, when salt deposit was formed, Lns were taken up by anhydrite more preferentially than by halite.

A PRELIMINARY INVESTIGATION ON THE DETERMINATION OF LANTHANOIDS, THORIUM AND URANIUM IN BRINE AND DEPOSIT OF A SALT LAKE IN CHINA

A brine sample and two deposit samples of a salt lake in China were analyzed for their contents of lanthanoids (Lns), thorium and uranium by neutron activation analysis. Five Lns were determined at sub ppb levels. Th and U contents were at about the same levels as those of Lns. The lanthanoid abundance patterns (Ln pattern) of the three samples are similar to each other, each having a negative slope in the light Ln region. There seems no substantial difference in distribution between the solution (brine) and solid (deposit) phases among Lns.

Temporal variation and provenance of thorium deposition observed at Tsukuba, Japan

Temporal variations of monthly thorium (Th) deposition observed at Tsukuba, Japan during the period 1990-2007, comparing with plutonium deposition, was studied. The monthly (232)Th deposition as did (239,240)Pu, varied according to season and inter-annually. In particular, (232)Th deposition increased significantly in spring coinciding with Asian dust (Kosa) events. The (230)Th/(232)Th activity ratios vary according to sources and can therefore be used to differentiate between locally derived and remotely derived (232)Th. The (230)Th/(232)Th activity ratios in deposition samples showed large variability with high ratios occurring in early spring. These high (230)Th/(232)Th ratios in deposition can be attributed to local dust storms, especially in early spring, that cause resuspension of soils from cultivated fields which are characterized by high (230)Th/(232)Th activity ratios. The results reveal that both locally and remotely derived (232)Th deposition showed seasonal variations with maxima in spring, although the remotely derived fraction is dominant rather than the locally derived one. The (232)Th deposition maxima later in spring is attributable to the remotely derived fraction, corresponding to the Kosa events. Annual (232)Th deposition exhibited an increasing trend, suggesting the presence of sources other than soil dust such as fly ash from increasing coal burning.

Mobility of radioactive cesium in soil originated from the Fukushima Daiichi nuclear disaster: application of extraction experiments

Extraction experiments on soil radioactively contaminated by the Fukushima Daiichi Nuclear Power Plant accident were conducted by using a variety of extractants to acquire knowledge on the mobility of radioactive cesium in soil. The experimental results revealed that cesium is tightly bound with soil particles and that radioactive cesium newly deposited on soil due to the accident had apparently a higher mobility than stable cesium commonly existing in soil. The results suggested that radioactive cesium deposited on soil hardly migrates via aqueous processes, although chemical and mineralogical conditions of soil affect their mobility.

Determination of Th and U at ppt levels in a neutral hot spring water by neutron activation analysis

Neutron activation analysis was successfully applied to the determination of Th and U at ppt levels in a neutral hot spring water. Blank test corrections were found to be essential to reach the final determined values. Normal NAA is a better method for the Th determination than epithermal NAA, while both NAAs are nearly equally effective for U determination.

Effects of pre-irradiation treatments in neutron activation analysis of rocks for measurements of their lanthanoid, thorium and uranium contents

Determination of the lanthanoids, thorium and uranium in silicate rocks has been investigated by neutron activation analysis (NAA). Seven or eight lanthanoids and thorium and uranium were determined by non-destructive instrumental NAA. The numbers of the lanthanoids determined were increased and errors on the final values were reduced by pre-irradiation treatments, which included a coprecipitation process with aluminium as collector to remove the alkali metals and halogens and a solvent extraction process to eliminate iron. The necessity of scandium removal was indicated.