Papers - 1986

If you need some copies of papers, please send e-mail to

[1986_01]

Surface modification of pyrolytic graphite due to deuterium and helium ionbombardments

K. Ashida, K. Kanamori, K. Ichimura, M. Matsuyama, K. Watanabe

J. Nucl. Mater., 137 (1986) 288-291

[1986_02] *The text is Japanese.

Capture and thermal release of hydrogen isotopes in/from pyrolytic graphite -Analysis of thermal desorption spectra-

K. Ashida, K. Ichimura, K. Watanabe

J. Vac. Soc. Japan, 29(5) (1986) 369-373

[1986_03] *The text is Japanese.

Absorption and desorption of hydrogen isotopes and isotopic waters by Zr-alloy getters

K. Ichimura, M. Matsuyama, K. Watanabe

J. Vac. Soc. Japan, 29 (1986) 364-368

[1986_04]

Activation processes of Zr-alloy getters observed with XPS-SIMS-TDS

K. Watanabe, K. Ichimura

Fusion Reactor Blanket and Fuel Cycle Technology, (Proc. Intern. Symp. Oct. 27-29, 1986, Tokai, Japan), (1986) 229-232

[1986_05]

Getterinng of tritium gas and tritiated water vapour by Zr-alloys

K. Ichimura, K. Watanabe, M. Matsuyama, T. Takeuchi

Fusion Reactor Blanket and Fuel Cycle Technology, (Proc. Intern. Symp. Oct. 27-29, 1986, Tokai, Japan), (1986) 221-224

[1986_06]

The synergism of β-rays and photons on the photoassisted catalytic decomposition of water over Pt/TiO₂

K. Watanabe, K. Ichimura, N. Inoue

Chem. Phys. Letters, 142(2) (1986) 196-198

[1986_07]

Separation factor in the photoassisted catalytic decomposition of tritiated water by Pt/TiO₂

K. Watanabe, K. Ichimura, N. Inoue, I. Matsuura

J. Phys. Chem., 90 (1986) 866-868

[1986_08]

Electret dosimeters for tritium beta-rays

T. Miki, M. Ikeya, M. Matsuyama, K. Watanabe

Radiation Protection Dosimetry, 17 (1986) 523-526

[1986_09]

Catalytic activities of Ni-alloys expressed by surface and bulk compositions

M. Matsuyama, K. Ashida, O. Takayasu, T. Takeuchi

J. Catal., 102 (1986) 309-315

[1986_10] *The text is Japanese.

The Formation of Fe-Ni Alloys by the Reduction with Hydrogen

M. Matsuyama, K. Ashida, T. Takeuchi

J. of Catal., 28(6) (1986) 417-420

[1986_11] *The text is Japanese.

Tritium Compatible Vacuum Systems

K. Watanabe

J. Vac. Soc. Japan, 29(10) (1986) 461-478

---

[1986_01]

Journal of Nuclear Materials, 137 (1986) 288-291

LETTER TO EDITORS

---

[1986_02] *The text is Japanese.

J. Vac. Soc. Japan, 29(5) (1986) 369-373

 Hydrogen isotopes implanted into graphite show broad thermal desorption spectra, which comprise three desorption peak denoted as peak I, II and III with increasing peak temperature. This study was devoted to deconvoluted the spectra with the aid of a stepwise detrapping method and to understand their desorption mechanisms. It was found that the peak I and II obeyed the second order kinetics with respect to the amount of trapped isotope atoms. This indicates that the rate determining steps for desorption are the recombination reactions of the trapped isotope atoms. The kinetic parameters determined are as follows: for peak I as

K_Id(H₂) = (1.5 x 10^-6) exp (-43 x 10³/RT)
K_Id(D₂) = (4.0 x 10^-7) exp (-44 x 10³/RT)
K_Id(T₂) = (9.3 x 10^-6) exp (-45 x 10³/RT)
And for peak II as
K_IId(H₂) = (7.5 x 10^-4) exp (-59 x 10³/RT)
K_IId(D₂) = (2.4 x 10^-4) exp (-59 x 10³/RT)
K_IId(T₂) = (1.3 x 10^-3) exp (-59 x 10³/RT)

 Where the frequency factor and activation energy are in [/molec. S] and [cal/mol] units, respectively. The considerably deviated frequency factors for T₂ appeare due to the presence of impurity gases, such as H₂O, CO, CO₂, and so on, in the tritium gas used.

---

[1986_03] *The text is Japanese.

J. Vac. Soc. Japan, 29 (1986) 364-368

 Zr-alloy getters have been applied to tritium handling and vacuum conditioning for fusion devices because of remarkably low dissociation pressure of hydride and large pumping speed for hydrogen, oxygen and carbon monoxide. For the application to tritium processing in fusion reactors, however, some of their properties should be improved. As a first step, we have examined the activation process of Zr₂Ni alloy using surface analysis equipments. In addition, absorption and desorption processes of hydrogen isotopes and isotopic waters were examined by thermal desorption spectroscopy. It was observed that the metallic Zr appeared by vacuum has above 400 °C. As a consequence, the alloy showed pumping action for various gases. It was revealed that the rate determining step in the absorption process is the dissociation of adsorbed molecules, while the rate determining step in the desorption process is the surface association of adsorbed atoms. The isotopic effects on activation energy for the absorption of hydrogen isotopes and isotopic waters were observed: 0.63 for H₂, 0.86 for D₂, and 0.72 for H₂O and 1.6 kcal/mol for D₂O. Similar isotopic effect was also observed for the desorption of hydrogen isotope molecules. The isotopic effects differed from each other for different alloys.

---

[1986_04]

Proc. Intern, Symp. On Fusion Blanket and Fuel Cycle Technology, (1986, Tokai, Japan) 229-232

 To develop getters suitable for tritium processing such as storage, supply, separation, and so on, we examined the alloying effects on the activation processes of Zr and Zr-alloys (Zr-Al, Zr-V-Fe, and Zr-Ni) by means of XPS-SIMS-TDS. It was observed that the formation of metallic Zr surface was the principal process for the activation, by which the getters showed pumping action for various gases. In the activation of Zr-alloys, a considerable alloying effect was observed: the activation temperature varied with alloying element. They were 900 °C for Zr, 800 °C for Zr-Al, 700 °C for Zr-Ni, and 400 °C for Zr-V-Fe. On the basis of surface characterization with XPS-SIMS and of TDS for impurity gases adsorbed on the as-received getter surface, it was concluded that the alloying effects on the activation temperature are determined with the balance between the stability of corresponding oxides and carbides present on the surfaces and the diffusivity of oxygen and carbon from the surface into the bulk.

---

[1986_05]

Proc. Interm. Symp. On Fusion Blanket and Fuel Cycle Technology, (1986, Tokai, Japan), 221-224

 Tritium processing such as supply, recovery, storage, and separation are of special importance for blanket technology as well as fuel cycling in fusion reactors. To obtain guiding principles to design suitable getters for each of the unit processes, we have studied the effects of alloying on the getter propertics using Zr-alloys. The activation energy for absorption varied considerably with alloying: it was 0.74 for Zr-Al, 0.01 for Zr-V-Fe, and 0.63 kcal/mol for Zr-Ni, whereas that for Zr has been reported as 19.2 kcal/mol. The heat of absorption also changed with alloying element as 32.0 - 33.4 (Zr-Al). That of hydrogen in Zr is reported as 15.6 - 30.6 kcal/mol. In addition, the ratio of the pumping sped of water vapor to that of hydrogen varied with alloying elements: for example, 1/40 for Zr-V-Fe and 1/4 for Zr-Ni at room temperature. The alloying effects mentioned above are considered due to modification of electronic structure of Zr with the alloying.

---

[1986_06]

CHEMICAL PHYSICS LETTERS, 124(2) (1986) 196-198

 The hydrogen evolution rate in photoassisted decomposition of water by Pt/TiO₂ was significantly enhanced in the presence of tritium (90 - 180 mCi/ml). The extent of the enhancement was proportional to the tritium concentration. This effect is attributed to the synergism of β-rays from tritium and photons on this decomposition reaction.

---

[1986_07]

The Journal of Physical Chemistry, 90(5) (1986) 866-868

  We measured first the hydrogen separation factor for the H₂O-HTO system in the photoassisted catalytic decomposition along with that for the H₂O-D₂O system. It was 15.4±0.2 for H₂O-HTO at the initial stage of the reaction. For H₂O-D₂O, it was 5.1±0.05 over a wide mixing ratio. These values are equivalent with those from electrolysis, indicating that the photoassisted decomposition proceeds with the same mechanism as the electrolysis. These results also confirmed that the catalytic process is the rate-determining step. The separation factors, however, decreased with reaction time to 6.2±0.05 (H₂O-HTO), 3.6±0.05 (H₂O-HDO), and 3.05±0.05 (D₂O-HDO) due to the gas-liquid equilibration reaction.

---

[1986_08]

Radiation Protection Dosimetry, 17 (1986) 523-526

 The decrease of the electret charge by exposure to gaseous tritium was studied in order to develop an electret personnel dosemeter for tritium. The electret charge decreases in proportion to the product of the tritium activity and the exposure time, corresponding to the theoretical response of electret dosemeters in the ionization chamber mode. The sensitivity is high enough to be of practical use. Several outstanding problems, especially the compensation of the contribution from atmospheric radon to the electret charge reduction, are discussed. A hybrid type electret dosemeter is proposed to compensate for the contribution of atmospheric radon and background gamma rays.

---

[1986_09]

JOURNAL OF CATALYSIS, 102 (1986) 309-315

 The surface compositions of three kinds of powdered alloys with different structures, Cu-Ni (fcc-fcc), Fe-Ni (bcc-fcc), and Co-Ni (hcp-fcc), were determined by the penetration of b-rays of ⁶³Ni mixed previously in the alloy, then the effect of the respective alloy structure both of the surface and of the bulk on the catalytic hydrogenation of ethylene was studied. The surfaces of these alloys were found to be Ni-poor for the wide range of alloy composition. The catalytic activity expressed by each surface composition was difficult to explain by the physicochemical properties of the surface. The activity expressed by the bulk composition of Cu-Ni of fcc structure was high in the region of unfilled d-band, and so were that of Fe-Ni and that of Co-Ni in the region of fcc structure. The activity of Fe-Ni for the dimerization of ¹⁴C-ethylene was studied, of whose activity the similar tendency was observed as found in the hydrogenation reaction. These could be interpreted as the results of the positive contribution of the dissolved hydrogen in bulk to the catalytic reactions.

---

[1986_10] *The text is Japanese.

J. of Catalysis, 28(6) (1986) 417-420

 The mechanism of the formation of non-uniform Fe-Ni alloys from the oxides of Fe and Ni by the reduction with hydrogen was studied. The change of the concentration of Ni on the surface during the reduction was measured by means of the penetration of β-ray of ⁶³Ni which was previously mixed with the oxides, and X-ray diffraction analysis for the bulk structure was carried out. The amount of ⁶³Ni in the mixed oxided decreased abruptly at the vicinity of final stage of the reduction. X-ray diffraction patterns showed that the bulk was composed of Ni-rich alloy and metallic Ni or Fe, and that the amount of Fe₃O₄ was kept constant even in 95%Ni oxide until the reduction of NiO had finished. THe rate of the reduction of NiO was greater than that of Fe₃O₄.
  The formation of Fe-rich surface and Ni-rich bulk was interpreted in terms of the difference in the rates of reduction of Fe₃O₄ and NiO. In addition, the mutual diffusion of Ni and Fe was taken into consideration.

---

[1986_11] *The text is Japanses.