A technique has been developed for oxygen depth profiling in a thickness range of 5 to about 100 mg cm−2 by activation with the16O(3He, p)18F reaction. An apparatus was set up for the activation of oxygen with a uniform probability along the depth, and a method
has been devised for step-wise etching of the activated sample. This technique has been applied to the study of oxygen behaviour
in heat treatment of silicon under various conditions.
Deuterium and15N were used as activable tracers for the study of the dissolution of hydrogen and nitrogen in silicon. Silicon was heated or zone-melted in D2-Ar, or heated in15N2-Ar after being covered with Si325N4. Depth profiles of D or15N in the resultant silicon samples were measured by the D(3He, p)4He or15N(, n)18F reaction combined with repeated HF–HNO3 etching. These two measurements have proved to be highly reliable and sensitive and to offer useful techniques in the study of trace concentrations of hydrogen and nitrogen in solid matrices.
Authors:Y. Kobayashi, K. Hirata, Y. Ujihira, and K. Itoh
Diffusion coefficients of positronium (Ps) in polycarbonate (PC) have been determined at temperatures between 20 and 300 K by means of positron lifetime spectroscopy. 2,2-dinitrobiphenyl (DNB) was added to the polymer as a Ps quencher and the diffusion coefficients were determined from measured Ps quenching rate constants, assuming that the reaction between Ps and DNB is completely diffusion-controlled.
Authors:Y. Yamada, M. Itoh, N. Kiriyama, K. Komura, and K. Ueno
All of the combustion water samples extracted from cellulose in pine tree rings corresponding to the 1983–1987 period showed elevated tritium concentrations of approximately 65 pCi/dm3, which were 30 to 35 pCi/dm3 higher than those for precipitation and atmospheric vapor in recent years. In addition, other environmental samples, viz. the tissue-free water in tree rings, and of combustion and tissue-free water in pine needles and spring water near the pine tree site also showed concentrations similar to the combustion water of cellulose. These findings suggest that most of the tritium in tree rings was supplied from underground water containing a high tritium concentration in the root zone of the pine tree.
Authors:T. Nozaki, Y. Itoh, S. Hayashi, and Q. Qiu
The sensitivity in the determination of deuterium and15N by nuclear reactions was examined for the following reactions: (1)15N(d,n)16O (or p+)+(6.13, 7.11 MeV); (2) D(3He,)4He (13 MeV); and (3)15N(,n)18F. By these activations with suitable etching techniques, sub ppm regions of D and15N have proved to be measurable with their depth profiles. Some fundamental properties of hydrogen and nitrogen in silicon are under investigation using of these activable tracers.
Authors:K. Sakamoto, Y. Hamajima, K. Itoh, and K. Yamazaki
Terrestrial zircon and apatite, as examples of uranium rich refractory minerals, and chromite, also highly refractory but
uranium poor, were neutron-irradiated for their133Xe release studies. Uranium determination by133Xe was found not to be successful in these refractory samples, due to incomplete fissiogenic-xenon release at 1600°C as revealed
by stepwise heating experiment. The high temperature release peaks appeared at ≾1500°C in these terrestrial minerals studied,
but at 1000∼1200°C in reported meteoritic whitlockite and chromite.
Authors:K. Sakamoto, Y. Hamajima, S. Yamaguchi, T. Takashima, and K. Itoh
Samples of an andesite (Asama-yama, Japan) and a basalt (Kilauea, Hawaii) were finely fractioned by density and the U distributions
among the separates were determined by homogenized fission track method. Groundmass was found to be enriched with U; one half
of the andesite U and almost all of the basalt U are accounted for by the groundmass U. Cerium and other REE are correlated
with U. In the andesite separates Na is accompanied by these elements, but Fe and Co are rather anticorrelated. Uranium concentrations
in the bulk samples and some of the separates were then compared with those determined by133Xe extracted by heating at 1600°C. Fissiogenic133Xe seems to become labile in groundmass, especially of the andesite, during reactor irradiations for 5 h or more. Stepwise
heating experiments suggested that133Xe in U-rich groundmass tends to escape at low temperatures and the remaining133Xe is mostly retained in highly refractory sites in phenocryst rather poor in U.
Authors:T. Hashizume, K. Terayama, T. Shimazaki, H. Itoh, and Y. Okuno
We succeeded in studying the mechanism of hydrogen added carbothermic reduction process of iron-manganese oxide by means of
the new technique, simultaneous measurement of evolved gas analysis (EGA) and humidity sensor (HS). Water vapor evolved by
the reduction with hydrogen can be detected by HS. Other gas was detected by TCD. Without carbon, the hydrogen reduction process
was followed to the formation of the intermediate product between MnO and FeO and finally reduction to the mixture of MnO
and Fe. With carbon, the intermediate products between MnO and FeO was formed at about 780 K. The methane was formed in higher
temperature than 1073 K and the reduction with carbon proceeded mainly. At higher temperatures, methane decomposed to yield
nascent carbon that tended to result in the acceleration of the reduction rate with carbon. The study is concerned with the
mechanism of the hydrogen reduction of MnFe2O4 and the effect of without and with carbon on this reduction by means of combining EGA and HS.
Authors:Y. Yamada, K. Yasuike, M. Itoh, N. Kiriyama, and K. Komura
Tritium concentration of organically bound hydrogen has been measured during the 1941 to 1987 period using a cellulose fraction
extracted from pine tree grown in Tatsunokuchi-machi, Ishikawa Prefecture, Japan. It was concluded that most of the tritium
bound in cellulose was supplied from the mixture of underground water in the root zone of the pine tree. Underground water
was strongly influenced by the precipitation and waters with different residence times.
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.