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[1984_01]
Journal of Nuclear Materials, 128 & 129 (1984) 792-797
K. ASHIDA, K. ICHIMURA, M. MATSUYAMA and K. WATANABE
Tritium Research Center, Toyama University, Gofuku 3190, Toyama 930, Japan
Abstract
Thermal release of hydrogen, deuterium and tritium
implanted into a pyrolytic graphite was studied by means of mass analyzed
thermal desorption spectroscopy along with surface characterization by
X-ray photoelectron spectroscopy. Hydrogen (or its isotopes) ions ware
implanted into the sample at room temperature with an applied voltage of
5 kV using a conventional ion gun. Subsequently, the sample was heated
to 900 C with various temperature ramps to measure the thermal desorption
spectra. The implanted hydrogen (or its isotopes) was predominantly desorbed
as H2 and in small amount as CH4. The desorption
spectra of H2 changed gradually while repeating the implantation-desorption
cycles and became reproducible after the total dose amounting to 1 x 1019
ion/cm2, Indicating that the virgin graphite is modified due
to formation/accumulation of radiation damage. For the modified graphite,
three desorption peaks were observed. The first peak is attributed to the
desorption of hydrogen atoms trapped on the carbon atoms in the normal
graphite lattice. The others correspond to differently trapped hydrogen
atoms in the graphite. The desorption of the first peak obeyed the second
kinetics with respect to the amount of the implantation, indicating that
the rate determining step is the surface association reaction of the hydrogen
atoms. The activation energy was estimated as 44 kcal/mol for three hydrogen
isotopes. However, the isotope effect appeared on the frequency factor:
their ratio was estimated as H2:D2:T2=3:1.5:1.
The desorption of methane obeyed the pseudo-first order kinetics with an
activation energy of 38 kcal/mol.
Key words: graphite, thermal desorption, tritium
[1984_02]
Int. J. Appl. Radiat. Isot., 35(7) (1984) 629-634
OSAMU TAKAYASU, YOSHIKI NAKANO and TOYOSABURO TAKEUCHI
Faculty of Science, Toyama University, Toyama 930, Japan
Abstract
The distribution of tritium on the surface layer of neutron-irradiated LiF was studied by means of autoradiography. The autoradiographs were compared with microphotographs of the surfaces which were chemically etched after the autoradiographs had been taken. Temperature-programmed desorption of tritium and u.v. absorption spectra were studied on the same sample. Many sharp lines appeared in the autoradiograph. Some of these lines are observed in the microphotograph, but some of them appeared only when the surface was etched. It was concluded from these results that tritium accumulates preferentially on step-edges and dislocations of the surface.
[1984_03]
J. Vac. Sci. Technol. A, 2(3) (1984) 1341-1347
Kenji Ichimura, Naoya Inoue, Kuniaki Watanabe, Toyosaburo Takeuchi
Tritium Research Center, Toyama University, 3190 Gofuku, Toyama 930, Japan
Abstract
Nonevaporable getters have wide applicability for
developing the tritium handing techniques for thermonuclear fusion devices.
From this viewpoint, mechanisms of the absorption and desorption of hydrogen
isotopes and the isotope effects were investigated for a Zr-V-Fe alloy
(St-707) by means of the mass analyzed thermal desorption spectroscopy.
It was observed that the absorption rate was proportional to the first
power of the pressure, indicating that the rate limiting step is the dissociative
adsorption of hydrogen isotopes on the surface. The activation was very
small, in the order of magnitude of a few tens of calories per mole in
a temperature rang from -196 to 200 °C. The desorption rate was proportional
to the amount of absorption, indicating that the rate limiting step is
the associative desorption reaction of hydrogen atoms or ions diffused
to the surface from the bulk. The rate constants for hydrogen and deuterium
were determined as
kd(H2) = (5.3+2.6-1.7)exp[-(28.0±0.7) x 103/RT] and
kd(D2) = (5.0+2.7-1.7)exp[-(28.6±0.8) x 103/RT] in [1/Pa 1 s],
respectively, where R is in [cal/mol deg]. With regard to tritium, the rate constant was evaluated as
kd(T2) = (5.0+20-4.0)exp[-(29.3±3) x 103/RT],
however, the frequency factor will have to be corrected
by knowing the relative sensitivity factor of the mass spectrometer for
tritium (T2).
PACS numbers: 68.45. Dq. 82.65. My
[1984_04]
Journal of Nuclear Materials, 128&129 (1984) 876-880
K. ICHIMURA, N. INOUE, K. WATANABE and T. TAKEUCHI
Tritium Research Center, Toyama University, 3190, Gofuku, Toyama 930, Japan
Abstract
Nonevaporable getters have wide applicability for
tritium handing systems. From this view point, the activation process of
the Zr-V-Fe getter (St-707) and absorption/desorption of D2O
on the getter surface were investigated, by means of XPS-SIMS and mass
analyzed thermal desorption spectroscopy.
XPS-SIMS measurements revealed that the getter
surface exposed to air was covered with adsorbed H2O, CO and
small amounts of hydrocarbons and that the getter components are oxidized.
Upon heating of the getter above 500 °C, the adsorbed species disappeared
from the surface, partly due to desorption and partly due to migration
into the bulk. Consequently, metallic Zr and V appeared on the surface,
whereas Fe disappeared. The surface composition was evaluated to be 87
at% Zr-13 at% V.
After the activation, water (D2O) was
readily absorbed into the getter at 300 °C in the form of deuterium atoms.
The absorption rate was proportional to the partial pressure of water,
indicating that the rate determining step for the absorption is the dissociation
of water molecules on the surface.
The absorption rate constant was 0.009 and 0.24
cc/s/cm2 (net surface area) [or 1.5 and 39 cc/s/cm2
(projected area)] at 25 and 300 °C, respectively. Only D2 was
desorbed from the getter exposed to D2O at 25 and 300 °C. The
rate determining step for the desorption is association of deuterium atoms
on the surface diffused from the bulk.
[1984_05]
JAPANESE JOURNAL OF APPLIED PHYSICS, 23(12) (1984) L931-L932
Toshikatsu MIKI, Motoji KEYA, Masao MATSUYAMA*, Kuniaki WATANABE*
Technical College, Yamaguchi University, Tokiwadai, Ube 755
*Tritium Research Center, Toyama University, Gofuku, Toyama930
Abstract
Response of an electret dosimeter for tritium beta-rays has been investigated by examining the charge decrease of polymer electrets by the exposure to tritium-involved air. The electret charge decreases proportionally to the tritium activity and the exposure time with a sensitivity of about 10-18 C/pCi·s, roughly corresponding to the theoretical response. Electret dosimeters can be used for the detection of tritium beta-rays of 10 pCi·h/cm3.
[1984_06]
JOURNAL of NUCLEAR SCIENCE and TECHNOLOGY, 21(1) (1984) 56-60
Kenji ICHIMURA, Masao MATSUYAMA, Kuniaki WATANABE
Tritium Research Center, Toyama University
Abstract
As a first step toward solving the problem of contamination
by tritium affecting secondary electron multipliers, the material used
in a marketed multiplier was studied in respect of adsorption and desorption
behavior, with application of thermal desorption spectroscopy.
It was found that the tritium adsorbed on the
material was desorbed in large part in the form of tritiated water, generated
by chemical reaction that combined adsorbed tritium with excess oxygen
present on the material and in small part in the form of tritiated hydrocarbons
produced by exchange reactions taking place between the tritium and hydrocarbons
also found adsorbed on the material surface. It was further indicated that
tritium desorption took place from two distinct kinds of adsorption/desorption
sites. Effective removal from the material was obtained of the adsorbed
tritium by heating in inert gas flow at 500 C for 6h. If a longer heating
time can be allowed, a lower heating temperature should be suffice for
decontamination.
[1984_07]
Nuclear Instruments and Methods in Physics Research, 226 (1984) 470-474
Kenji ICHIMURA and Kuniaki WATANABE
Tritium Research Center, Toyama University, 3190 Gofuku, Toyama 930, Japan
Kazunari NISHIZAWA
Faculty of Engineering, Osaka University, Osaka 565, Japan
Junji FUJITA
Institute of Plasma Physics, Nagoya University, Nagoya 464, Japan
Abstract
A ceramic secondary electron multiplier (SEM), Ceratron, was
used to study impairment of the SEM performance due to adsorbed tritium,
its decontamination, and the applicability of the SEM to measure tritium
pressure. The background level of the SEM increased significantly, up to
its counting limit, due to tritium adsorption. Heating it to 300 C in vacuo
and/or in the presence of reactive gases such as D2
and CO at 1 x 10-4 Pa was not effective to decontaminate the
SEM, whereas photon irradiation was extremely powerful for the decontamination.
The tritium (HT) pressure in a range of 1 x 10-6-1
x 10-3 Pa could be measured with no significant impairment of
the SEM performance with the aid of photon irradiation. It is revealed
that a particle flux as low as 1 particle/s will be able to measure in
the presence of tritium if suitable photon sources are installed in the
systems.
[1984_08]
JOURNAL OF MOLECULAR SPECTROSCOPY, 104, 405-413 (1984)
NOTES
The IR Spectrum of T218O
I. KANESAKA, M. TSUCHIDA, K. KAWAI, and T. TAKEUCHI
Faculty of Science, Toyama University, Gofuku, Toyama 930, Japan