In Situ Evolution of Pores in Lithium Hydride at Elevated Temperatures Characterized by X-ray Computed Tomography

The evolution of defects such as pores at elevated temperatures is crucial for revealing the thermal stability of lithium hydride ceramic. The in situ evolution of pores in sintered lithium hydride ceramic from 25 °C to 500 °C, such as the statistics of pores and the 3D structure of pores, was investigated by X-ray computed tomography. Based on the statistics of pores, the porosity significantly increased from 25 °C to 200 °C and decreased after 200 °C, due to the significant change in the number and total volume of the round-shaped pores and the branched crack-like pores with an increasing temperature. According to the 3D structure of pores, the positions of pores did not change, and the sizes of pores went up in the range of 25–200 °C and went down after 200 °C. Some small round-shaped pores with an Equivalent Diameter of less than 9 μm appeared at 200 °C and disappeared at elevated temperatures. Some adjacent pores of all types connected at 200 °C, and some branched crack-like pores gradually disconnected with an increasing temperature. The expansion of pores at 200 °C caused by the release of residual hydrogen and the contraction of pores after 200 °C because of the migration and diffusion of some hydrogen in pores might be the reason for the evolution of pores with an increasing temperature.

PECULIARITIES OF CHANNELING AND GENERATED RADIATION OF RELATIVISTIC ELECTRONS IN THE MAIN CHARGED AXES OF LITHIUM HYDRIDE CRYSTAL

The paper deals with the calculation of electron interaction potentials with the main charged [110] axes in a lithium hydride crystal at T = 300, 600, and 900 K temperatures. For relativistic electrons with Lorentz factors γ = 50, 75, 100 the energy and corresponding wave functions of transverse levels of channeling motion are found numerically. The radiation spectra of channeling electrons with (and without) accounting an angular dispersion are calculated on the basis of these data.

Detection of deuterated molecules, but not of lithium hydride, in the z = 0.89 absorber toward PKS 1830−211

Deuterium and lithium are light elements of high cosmological and astrophysical importance. In this work we report the first detection of deuterated molecules and a search for lithium hydride, 7LiH, at redshift z = 0.89 in the spiral galaxy intercepting the line of sight to the quasar PKS 1830−211. We used ALMA to observe several submillimeter lines of ND, NH2D, and HDO, and their related isotopomers NH2, NH3, and H218O, in absorption against the southwest image of the quasar, allowing us to derive XD/XH abundance ratios. The absorption spectra mainly consist of two distinct narrow velocity components for which we find remarkable differences. One velocity component shows XD/XH abundances that is about 10 times larger than the primordial elemental D/H ratio, and no variability of the absorption profile during the time span of our observations. In contrast, the other component shows a stronger deuterium fractionation. Compared to the first component, this second component has XD/XH abundances that are 100 times larger than the primordial D/H ratio, a deepening of the absorption by a factor of two within a few months, and a rich chemical composition, with relative enhancements of N2H+, CH3OH, SO2 and complex organic molecules. We therefore speculate that this component is associated with the analog of a Galactic dark cloud, while the first component is likely more diffuse. Our search for the 7LiH (1–0) line was unsuccessful and we derive an upper limit 7LiH/H2 = 4 × 10−13 (3σ) in the z = 0.89 absorber toward PKS 1830−211. Besides, with ALMA archival data, we could not confirm the previous tentative detections of this line in the z = 0.68 absorber toward B 0218+357; we derive an upper limit 7LiH/H2 = 5 × 10−11 (3σ), although this is less constraining than our limit toward PKS 1830−211. We conclude that, as in the Milky Way, only a tiny fraction of lithium nuclei are possibly bound in LiH in these absorbers at intermediate redshift.