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- Author or Editor: H. Nakahara x
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Abstract Â
Mass yield curves of spontaneous fissions, thermal-neutron induced fissions, monochromatic-neutron and proton induced fissions of actinides are reviewed. Mean masses of light and heavy asymmetric mass yield peaks are listed. The subtle change of the shape of the asymmetric heavy peak is expressed in terms of the parameters of two Gaussians that fit the observed data well. One Gaussian is narrow in width and always peaks at A=133–136 while the other is broader and peaks at A=140–144. The FWHM of the heavy asymmetric peak becomes minimum for the fissioning mass A=240–245. An analysis of the projectile energy dependence of mass yield curves indicated, at least, two distinctively different behaviors, one for asymmetric products and the other for symmetric products. From the energy dependence of the peak-to-valley rations, the 
extra-energy
required for symmetric mass division, or the difference in the fission barrier heights, in the nomeuclature of the two-mode hypothesis, is deduced for a wide range of fission nuclides.
Abstract Â
Simple and effective procedures for the determination of Re, Os and Ir by radiochemical neutron activation analysis are presented. Those elements are separated individually by distillation (for Os) and anion exchange techniques (for Re and Ir) for a single specimen. Reproducibilities of the data obtained by the present procedures are evaluated by replicate analyses of the Allende meteorite sample, and are deduced to be 3% for Re, 6% for Os and 4% for Ir (1
). Detection limits for the present procedures are calculated to be 1 ppb for Re, 20 ppb for Os and 5 ppb for Ir. These procedures were applied to Antarctic meteorites and proved to work very effectively for the determination of trace Re, Os and Ir in chondrite meteorites.
Summary Â
A portable liquid scintillation counter was applied for the analysis of alpha-ray energy spectrum to determine the ratio of 220Rn/222Rn in fumarolic gas in the field. A surface-polished vial was developed, by which a Gaussian distribution could be approximated for the alpha-ray energy spectra and the peak areas of the nuclides could be estimated independently, because of the wide FWHM in the liquid scientillation pulse. A fumarolic gas sample was collected in Mt. Kamiyama (Hakoneyama geothermal field in Japan) having low 220Rn/222Rn ratio of 2.20±0.13.
Abstract Â
Environmental effects on plants caused by geothermal resource development were studied. Neutron activation method was found most suitable for this kind of multi-element analysis, and 24 elements could be identified and determined without any chemical separation. When the amounts of chemical elements detected in plants were plotted against the distance from the source well, clear correlations sould be observed for Na, Cl, Rb, Cs, As and Sb. Those turned out to be the elements especially concentrated in the geothermal hot water. From the present studies it was concluded that plants growing within the radius of 300 to 400 meters from the source well were affected by chemical pollutants carried over by mist particles.
Abstract Â
Environmental effects of geothermal waste water discharged into the neighbouring streams were investigated by ordinary chemical analyses and by the neutron activation method. Results show that serious effects of a large amount of discharge in the past are still retained in the sediments of the near-by water system. It was also found that As and Cs are the best chemical species for tracing the long-standing effects of past discharge.
Abstract Â
Chlorine, bromine and iodine (hereafter, halogens) were detemined for rock samples by radiochemical neutron activation analysis. The powdered samples and reference standards prepared from chemical reagents were simultaneously irradiated for 10 to 30 minutes with or without a cadmium filter in a TRIGA-II reactor at the Institute for Atomic Energy, Rikkyo University. The samples were subjected to radiochemical procedures of halogens immediately after the irradiation. Iodine was firstly precipitated as PdI2, and chlorine and bromine were successively precipitated as Ag-halides at the same time. In this study, geological standard rocks, sedimentary rocks and meteorites were analyzed for trace halogens. In some Antarctic meteorites, iodine contents were observed to be anomalously high. Chlorine contents also are somewhat high. The overabundance of iodine and chlorine must be caused by terrestrial contamination on the Antarctica.
Abstract Â
In Japan, cosmetics claiming hormesis effect are available through Internet. Although these cosmetics show the contents, they never mention the minor elements and radioactive sources. The existence of radioisotopes, however, was observed by measurements of the gamma-rays with a HPGe detector. In this study, in order to clarify the contents of trace elements, the hormesis cosmetics including radioactive sources were analyzed using INAA, PGAA and NAA with multiple gamma-ray detection (NAAMG). Nineteen elements were analyzed quantitatively in hormesis cosmetics by INAA, PGAA and NAAMG and 16 elements were detected qualitatively by SEM-EPMA.
Abstract Â
Radiochemical techniques have been applied in various ways to the study of fullerenes and metallofullerenes for the past several years, and they have provided invaluable information pertaining to the stability, structures, and formation of the novel carbon material. This paper reviews those experimental results that have fully shown the usefulness and uniqueness of radionuclides demonstrated in the field of fullerene science.
Abstract Â
Samples of two older geochemical reference rocks GSJ JG-1 (granodiorite) and JB-1 (basalt) and three new ones GSJ JA-1 (andesite), JR-1 (rhyolite) and JB-2 (basalt) were subjected to determination of lanthanoid elements by radiochemical neutron activation analysis. The contents of 9 lanthanoid elements could be re-determined for the older reference rocks and those of 11 elements were determined for the new rocks. The results were compared with the previously published data.
Abstract Â
The stability of 16 kinds of metallofullerenes (9 elements) was investigated against the recoil phenomena associated with the capture of neutrons by the metal atoms inside the carbon cages. The yields of the unaffected species were obtained by use of the HPLC separation method and radioactivity measurements. Recoil energy distributions of the metal atoms were calculated theoretically and the effective energy required for destruction of metallofullerenes from inside by recoiling atoms was estimated to be about 10 to 15 eV for the metallofullerenes containing lanthanide atoms.
