Estimate of Fukushima-derived radiocaesium in the North Pacific Ocean in summer 2012.

Distributions of radiocaesium (134Cs and 137Cs) derived from the Tokyo Electric Power Company (TEPCO) Fukushima Dai-ichi Nuclear Power Plant (FNPP1) accident in the North Pacific Ocean in the summer of 2012 were investigated. We have estimated the radiocaesium inventory in the surface layer using the optimal interpolation analysis and the subducted amount into the central mode water (CMW) by using vertical profiles of FNPP1-134Cs and mass balance analysis as the first approach. The inventory of the 134Cs in the surface layer in the North Pacific Ocean in August-December 2012 was estimated at 5.1 ± 0.9 PBq on 1 October 2012, which corresponds to 8.6 ± 1.5 PBq when it was decay corrected to the date of the FNPP1 accident, 11 March 2011. It was revealed that 56 ± 10% of the released 134Cs into the North Pacific Ocean, which was estimated at 15.3 ± 2.6 PBq, transported eastward in the surface layer in 2012. The amount of 134Cs subducted in the CMW was estimated to be 2.5 ± 0.9 PBq based on the mass balance among the three domains of the surface layer, subtropical mode water, and CMW.

Gamma-ray detection efficiency of the microchannel plate installed as an ion detector in the low energy particle instrument onboard the GEOTAIL satellite.

A microchannel plate (MCP) assembly has been used as an ion detector in the low energy particle (LEP) instrument onboard the magnetospheric satellite GEOTAIL. Recently the MCP assembly has detected gamma rays emitted from an astronomical object and has been shown to provide unique information of gamma rays if they are intense enough. However, the detection efficiency for gamma rays was not measured before launch, and therefore we could not analyze the LEP data quantitatively. In this article, we report the gamma-ray detection efficiency of the MCP assembly. The measured efficiencies are 1.29%+/-0.71% and 0.21%+/-0.14% for normal incidence 60 and 662 keV gamma rays, respectively. The incident angle dependence is also presented. Our calibration is crucial to study high energy astrophysical phenomena by using the LEP.

Effects of the nuclear genome on selective transmission of mitochondrial DNA in Drosophila.

In mitochondrial DNA (mtDNA) heteroplasmy in Drosophila, we previously reported that mtDNA was selectively transmitted depending on temperature (Matsuura et al., 1991). To investigate the effects of nuclear genome on the temperature-dependent transmission, two sets of heteroplasmy were constructed by germ-plasm transplantation, and changes in the relative proportion of two types of mtDNA were examined at 19 degrees C and 25 degrees C. In heteroplasmy possessing D. melanogaster and D. mauritiana mtDNA, two different nuclear genomes of D. melanogaster were examined after reciprocally substituting the nuclear genomes. In heteroplasmy possessing D. simulans and D. mauritiana mtDNA, nuclear genomes of D. melanogaster, D. simulans and D. mauritiana were used. For each set of mtDNA combination, the modes of temperature-dependent transmission of mtDNA differed according to the nuclear genome used. From these and our previous results (Matsuura et al., 1991; Tsujimoto et al., 1991), it is clear that the temperature-dependent transmission of mtDNA is affected by nuclear genome. This suggests that the nuclear genome is involved in determining the temperature-dependency of mtDNA transmission.