Nickel sulfide (NiS) fire assay was used for the pre-concentration of Ir and Au in rock samples. The beads obtained after
fire assay were irradiated directly with neutrons to determine Ir and Au. To suppress the reaction of 58Ni(n,p)58Co, the fire assay was carried out by using a small amount of Ni (0.0625 g) and the NiS bead samples were irradiated by neutrons
with high Cd ratios. Analytical results of Ir and Au for rock samples were close to literature values, confirming that our
procedure of INAA with pre-concentration can be applied to rock samples for the determination of ppb to sub-ppb level of Ir
Prompt gamma-ray analysis was applied to determine hydrogen in geological samples. In order to obtain accurate values, blank
values were estimated and subtracted. Samples were dried to constant weight in an oven. Helium gas was introduced into the
sample box to purge the air containing moisture during the measurement. Hydrogen contents in some geochemical standard samples
were determined and highly reproducible values were obtained.
In order to determine thorium and uranium traces in geochemical and cosmochemical samples, we developed an ICP-MS procedure, in which an anion-exchange step was introduced after sample digestion to separate major matrix elements, leading to decrease the dilution factor and increase the sensitivity for Th and U. The ICP-MS procedure was compared to the RNAA procedure which we recently developed for the same purpose. Both ICP-MS and RNAA procedures developed were found to yield similar detection limits (sub ppb) for Th and U.
Radiochemical neutron activation analysis (RNAA) was applied to geochemical and cosmochemical samples to determine trace amounts
of Mo and W. To determine the Mo concentration by NAA accurately, the contribution of the fission products of U should be
corrected. For that reason, we developed a simple and effective method, where a contribution of fissiogenic 99Mo was estimated by monitoring the ratio of uranium fission-product 99Mo to 133I. Mo concentrations corrected for fission with the W concentrations were consistent with the literature values, showing that
133I was found to be an effective monitor for fission correction. Detection limits are estimated to be 10 ppb for Mo and W and
30 ppb for U under the present experimental conditions.
Authors:Y. Oura, T. Ohtsuki, K. Hirose, and M. Ebihara
We introduce the status of the 300-MeV electron linear accelerator used for radioanalytical studies at Tohoku University.
In the accelerator facility, several scientific programs for producing radioactivities and use have been performed in several
fields, such as photon activation analysis, study of nuclear phenomena influenced by chemical nature, radioisotope production
for trace elements, radiation chemistry and irradiation effects by electrons and photons, radioisotope labeling and its mechanism.
We show the outlook of the facility, instrumental developments of a beam-course, an irradiation system and several measurement
devices. Further, we display a radioanalytical topic in practice, evaluation of trace amount of potassium in high-purity reagent
of Gd2O3 by photon activation analysis.
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.
Authors:K. Sueki, Y. Oura, W. Sato, H. Nakahara, and T. Tomizawa
Nondestructive determination of major and trace elements within voluminous materials has been demonstrated by prompt γ-ray
neutron activation analysis. Some fragmented pieces of pottery bowls considered to have been produced in the late 18th century
were analyzed by a new internal monostandard method, and noticeable differences of the elemental contents and significant
correlations of the elemental distributions were observed among the samples. The possibility of identification of producing
areas of unearthened material is demonstrated by the analytical results and the applicability of this method to the investigation
of precious samples in a completely nondestructive way is verified in practice.
Authors:J. Chai, Y. Miyamoto, Y. Kokubu, M. Magara, S. Sakurai, S. Usuda, Y. Oura, and M. Ebihara
In order to search for isotopic anomalies of U caused by the disintegration of 247Cm in meteorite samples, an analytical scheme for determining 235U/238U ratio for a small amount of uranium (less than 1 ng U) was established. The isotopic ratio of U was determined by double-focusing
inductively coupled plasma mass spectrometry (DF-ICP-MS). With a great improvement of chemical procedure for purifying the
uranium fraction separated from meteorite samples, a variation in 235U/238U ratios was resolved at an order of ±4‰ for 100 ppt or 200 pg U in solution. For applying the procedure in searching an evidence
of 247Cm as an extinct radionuclide in the early solar system, a selective chemical dissolution of constituent minerals of meteorites
using EDTA and HCl was introduced and a chemical purification scheme of uranium for ICP-MS was established.
Authors:C. Kim, Y. Oura, Y. Takaku, H. Nitta, Y. Igarashi, and N. Ikeda
Fission track /FT/ method and inductively coupled plasma mass spectrometry /ICP-MS/, that is a new analytical technique for the analysis of trace element, were used for the measurement of240Pu/239Pu ratios in environmental samples. The results obtained by both methods are in agreement within the relative deviation of 9–13%. The precision in ICP-MS was found to be better than in it the FT-method. These methods are applicable to measure the Pu isotopes ratio at low concentration levels in environmental samples.
Authors:M. Oshima, Y. Toh, A. Kimura, M. Ebihara, Y. Oura, Y. Itoh, H. Sawahata, and M. Matsuo
By combining neutron activation analysis with multiple gamma-ray detection (gamma-gamma coincidence), we have proved better
sensitivity and resolution for the trace element analysis than the ordinary single gamma-ray detection method. We now try
to apply the multiple gamma-ray detection method to the prompt gamma ray analysis (PGA). We have established a new cold neutron
beam line for PGA in Japan Research Reactor, JRR-3M, at Tokai establishment of Japan Atomic Energy Research Institute (JAERI).
It consists of a beam shutter, a beam attenuator, a gamma-ray detector array, a sample changer, and a beam stopper. We construct
a high-efficiency gamma-ray detector array specially designed for this purpose. Its performance has been evaluated with the
Monte Carlo simulation code, GEANT 4.5.0.