Nobuyuki M. Masaki

Study on Sorption of Tritium on Various Material Surfaces and Its Application to Decontamination of Tritium-Sorbing Materials

Behavior of sorption of tritium on surfaces of stainless steel, aluminum and borosilicate glass has been studied using gaseous tritium with high specific activity and the newly obtained knowledge has been applied to chemical and thermal decontamination of tritium-sorbing materials. The behavior depends on a character of surface of each material. The total amount of sorbed-tritium is evaluated a function of time of exposure to gaseous tritium. The depth-profile of sorbed-tritium is obtained by chemical etching method. From these results, practical samples of stainless steel were decontaminated. The vacuum-bakeout for 24 hours at 773 K and dissolution by dilute (5%) HCl for 2 hours enable the authors to obtain the decontamination factor of 200.

Nuclear Magnetic Moment of the First Excited State (I= 2 +) of 238U

The 238 U Mossbauer effect of UO 2 has been investigated in the temperature range from 5.4 K to 280 K. Nuclear Zeeman splitting of the 238 U nucleus in antiferromagnetic UO 2 at 5.4 K is 59.1±3.9 mm s -1 and corresponds to the value of 252.3±0.5 T obtained by the 235 U pulsed NMR technique. The nuclear magnetic moment of the first excited state ( I =2 + ) of 238 U has been determined to be 0.254±0.015µ N . The conversion factor of 4.27±0.28 T/mm s -1 enables us to determine the hyperfine magnetic field at the 238 U nucleus using 238 U Mossbauer spectroscopy. The temperature dependence of the recoil-free fraction of the 238 U Mossbauer effect in UO 2 has been discussed.

Dynamical calculations for the H+para, ortho‐H2 reactions at low temperatures: Effect of rotational energy of reagent H2 molecule

The reactive probabilities for the H+H2( j=0,1)→H2( j ’=0,1)+H reactions are calculated at low translational energies using a simplified Jz ‐conserving coupled‐states method. Both the LSTH and the PK2 potential energy surfaces are used. The energy where the Wigner threshold behavior appears is affected both by the existence of van der Waals well included in the potential surface and by the rotational state of H2. Thermal rate constants at low temperatures are calculated for the title reactions, and the calculated values are compared with the experimental results in solid phase reported by others. The effect of rotational energy of reagent H2 molecule on the rate constants is discussed.

Mössbauer spectroscopic study of frozen solutions of57Co using a specially designed cryostat for time differential coincidence emission Mössbauer spectroscopy of237Np

Experiments on the57Fe Mössbauer effect in frozen solutions were carried out in order to demonstrate the capabilities of a cryostat which was developed for the emission Mössbauer spectroscopy of237Np. We confirmed the existence of an aliovalent state of57Fe in the temperature range from 5.5 to 35 K. However, the relative amounts of Fe(II) and Fe(III) in the frozen matrix were almost constant for the temperature range from 5.5 to 150 K. The design, operation and capabilities of the cryostat are also described.

151Eu Mössbauer Spectroscopic Study on the EuyM1-yO2-x (0 ≤ y ≤ 1.0) (M=Th, U)

151Eu-Mössbauer spectroscopic and powder X-ray diffraction (XRD) study has been performed for the EuyU1-yO2-x (M=Th, and U) systems over the entire composition range of 0 ≤ y ≤ 1.0. The XRD results of the Eu-Th system showed that a very wide defect-fluorite (DF) type phase in which oxygen-vacancies (Vo) are disordered (x=y/2) is formed for 0 ≤ y ≤ 0.5 and that two-phases regions sandwitching a narrow C-type (C) single phase around y ≈ 0.8 appear for 0.5 < y < 0.8 (DF + C) and 0.82 < y < 1.0 (C + B-type (monoclinic) Eu2O3). The Mossbauer results show that the isomer shifts (ISs) of Eu3+ in this system smoothly increase with Eu composition, y. The decrease of average coordination number (CN) of O2− around Eu3+ with y (CN=8-2y)(x=y/2) results in the decrease of the average Eu-O bond length, which is due to the decrease of repulsion force between O2- anions. This result confirms that the IS of Eu3+ correlates well with the average Eu-O bond length in oxide systems. For the Eu-U system, also the defect-fluorite (DF)-type solid solution phase is formed for y < 0.5, but the lattice parameter (a0) of the system decreases almost linearly with y, in accordance with the calculated a0 vs. y curve for the oxygen-stoichiometric (i.e. x=0) fluorite dioxide (CN=8). Consistent with this XRD result, the ISs of Eu3+ in this composition range are smaller than those of the Eu-Th system and remain almost constant around 0.5 mm/s, which is comparable to those of pyrochlore oxides (Eu2Zr2O7 and Eu2Hf2O7 (y=0.5)) with O2--8 fold coordinated Eu3+(CN=8).

151Eu Mössbauer spectroscopic and XRD study on some fluorite-type solid solution systems, EuyM1−yO2−y/2 (M=Zr, Hf, Ce)

151Eu Mossbauer spectroscopy and powder x-ray diffractometry (XRD) have been applied to elucidate the local structure around the trivalent europium (Eu3+) in the titled three defect-fluorite systems. From this study, it has been clarified that in contrast to Eu-Ce system the stabilized cubic-fluorite phase in Eu-Zr and Eu-Hf systems has most likely a pyrochlore-type local structure (microdomain structure).

Mössbauer spectroscopic studies of 237Np in aqueous solutions

We applied Mössbauer spectroscopy to 237Np in aqueous solutions to study chemical states. A sample solution was adjusted to 50 mg/ml of Np(V) concentration in 0.6 M nitric acid solution. This solution was put into original designed containers for Mössbauer spectroscopy. Mössbauer spectra were measured in the transmission geometry at 11 K using cryostat, after containers with a sample solution was mounted to a sample holder and soaked into liquid nitrogen to freeze quickly. Mössbauer spectrum was observed 16 absorption lines with quadruple splitting and magnetic splitting. The value of isomer shift of Np(V) in 0.6 M nitric acid was -17.4(1) mm/s at 11 K. Isomer shift value reflects valence and coordination number. It was found that Np(V) had 7 coordination numbers in 0.6 M nitric acid solution from values of isomer shift that had been measured for neptunyl compounds.

ESR study of hydrogen atoms in solid nitrogen

Abstract The preparation and ESR investigation of H atoms in a solid N 2 matrix at liquid helium temperatures are reported. The trapping site for the atoms is determined by the analysis of the superhyperfine structure of the ESR spectrum. The temperature stability and recombination of atoms were studied. The estimate of the recombination rate constant was obtained at 11.5 K.

Chemical Behavior of Tritium in/on Various Materials

In this paper, the chemical interaction of tritium with various materials is studied. The chemical state of tritium resting in materials depended on their chemical and physical conditions. The state of tritium can be classified into four categories, chemically bounded tritium, molecularly trapped tritium, tritium trapped as atomic state, and tritium localized in a special part. These chemical states in or on materials controlled the diffusivity of tritium in them and release from their surfaces. The chemical properties of materials mainly affect the resting state of tritium, but in some cases, the effects of physical properties are more important than those of the chemical ones.

Release Enhancement of Tritium from Graphite by Addition of Hydrogen

The release behavior of tritium from graphite was studied in pure He and He + H, atmosphere. The release from powdered graphite was significantly enhanced in a hydrogen environment. Apparent diffusion coefficients of tritium in graphite also became much higher in an atmosphere containing hydrogen than values obtained in pure helium atmosphere. A careful investigation of the release processes resulted in the conclusion that the most important process of tritium behavior in graphite was diffusion, but the desorption process of tritium from the surface played a significant role. The enhancement of the desorption process was controlled by atomic hydrogen.