511 keV line and diffuse gamma rays from moduli

We obtain the spectrum of gamma ray emissions from the moduli whose decay into $e^+ e^-$ accounts for the 511 keV line observed by SPI/INTERGRAL. The moduli emit gamma rays through internal bremsstrahlung, and also decay directly into two gammas via tree and/or one-loop diagrams. We show that the internal bremsstahlung constrains the mass of the moduli below $\sim 40$ MeV model-independently. On the other hand, the flux of two gammas directly decayed from the moduli through one loop diagrams will exceed the observed galactic diffuse gamma-ray background if the moduli mass exceeds $\sim 20$ MeV in the typical situation. Moreover, forthcoming analysis of SPI data in the range of 1-8 MeV may detect the line emisson with the energy half the moduli mass in the near future, which confirms the decaying moduli scenario.Comment: 6 pages, 5 figures, published versio

A Surrogate Approach to Reveal Microstructural Mechanisms Controlling the 3D Short Crack Growth in a Ti-6Al-4V Alloy

Microstructural features and short crack growth behavior were characterized and linked in a Ti-6Al-4V by employing X-ray micro-tomography combined with EBSD serial sectioning. Statistical analysis was used to rank the contributing features to the crack behavior. Afterwards, by creating surrogate models, the microstructural mechanism controlling the short crack behavior were revealed. Short crack preferably grows inside the predominant α phase above the average microstructural fraction. A high number of grains in contact with cracked α grains elongated in the loading direction may impose a constraint on the crack opening resulting in low crack growth rates. As the crack front becomes larger, the increase in the shear stress field away from the cracked grain leads to crack bifurcations, resulting in a decrease in crack driving forces with low crack growth rates. This leads to a preferable growth in α+β phase and along the interface above the average microstructural fractions

A Surrogate Approach to Reveal Microstructural Mechanisms Controlling the 3D Short Crack Growth in a Ti-6Al-4V Alloy

Microstructural features and short crack growth behavior were characterized and linked in a Ti-6Al-4V by employing X-ray micro-tomography combined with EBSD serial sectioning. Statistical analysis was used to rank the contributing features to the crack behavior. Afterwards, by creating surrogate models, the microstructural mechanism controlling the short crack behavior were revealed. Short crack preferably grows inside the predominant α phase above the average microstructural fraction. A high number of grains in contact with cracked α grains elongated in the loading direction may impose a constraint on the crack opening resulting in low crack growth rates. As the crack front becomes larger, the increase in the shear stress field away from the cracked grain leads to crack bifurcations, resulting in a decrease in crack driving forces with low crack growth rates. This leads to a preferable growth in α+β phase and along the interface above the average microstructural fractions

Spectroscopic and first-principles calculation studies of the chemical forms of palladium ion in nitric acid solution for development of disposal of high-level radioactive nuclear wastes

We have investigated the chemical forms of palladium (Pd) ion in nitric acid solution, using XAFS/UV-vis spectroscopic and first-principles methods in order to develop the disposal of high-level radioactive nuclear liquid wastes (HLLW: radioactive metal ions in 2 M nitric acid solution). The results of theoretical calculations and XAFS/UV-vis spectroscopy indicate that Pd is a divalent ion and forms a square-planar complex structure coordinated with four nitrate ions, [Pd(NO3)4]2-, in nitric acid solution. This complex structure is also thermodynamically predicted to be most stable among complexes [Pd(H2O)x(NO3)4-x]x-2 (x = 0-4). Since the overall feature of UV-vis spectra of the Pd complex was independent of nitric acid concentration in the range 1–6 M, the structure of the Pd complex remains unchanged in this range. Furthermore, we examined the influence of γ-ray radiation on the [Pd(NO3)4]2- complex, using UV-vis spectroscopy, and found that UV-vis spectra seemed not to be changed even after 1.0 MGy irradiation. This implies that the Pd complex structure will be still stable in actual HLLW. These findings obtained above are useful information to develop the vitrification processes for disposal of HLLW