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.
Authors:H. Yoshikawa, T. Nakanishi, and H. Nakahara
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.
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.
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.
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.
Authors:E. Furuta, H. Nakahara, Y. Hatsukawa, H. Matsue, and H. Sakane
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
Authors:M. Ebihara, H. Ozaki, F. Kato, and H. Nakahara
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.
Authors:M. Tsukada, H. Yoshikawa, M. Yanaga, K. Endo, and H. Nakahara
Use of an enriched156Dy isotope as an activable yield tracer for the determination of lanthanoid contents in various biological reference materials has been proposed. The method consists of preconcentration of the lanthanoid in the156Dy doped samples followed by neutron irradiation and further chemical purification steps. The chemical behaviour of lanthanoid elements in the whole procedure was found, in separate runs, similar to that of the added156Dy within experimental errors. Simple purification steps after irradiation allow the measurement of relatively short-lived nuclides and diminish the radiation dose received during the chemical treatment. The present results for orchard leaves (NBS SRM 1571) are generally in good agreement with the previously reported data. Some new data are obtained for other biological reference materials.
Authors:M. Tsukada, D. Yamamoto, H. Yoshikawa, K. Endo, and H. Nakahara
Use of an enriched isotope as an activable tracer is proposed for the preconcentration of trace elements in neutron activation analysis. As a test of this method, contents of cadmium in various biological standard samples were determined by addition of an enriched116Cd tracer in the preconcentration step followed by neutron irradiation and -ray spectrometry. The principle, advantage, and limitations of the method are also discussed.
Authors:Y. Oura, S. Enomoto, H. Nakahara, H. Matsue, and C. Yonezawa
Prompt -ray analysis with the internal monostandard method was used to organs taken from rats. After B or Cd was administered, the B/H and Cd/H contents ratios were determined in the brain, kidney, and liver to study their distribution and metabolism. Boron was distributed in all organs but metabolized quickly. Cd was slowly accumulated in the liver and kidneys during the 65 hours studied but no Cd was detected in the brain.