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1. chinaXiv:201708.00285 [pdf]

The behaviors of helium atoms in tantalum, rhenium and osmium

Subjects: Physics >> General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.

We present systematic first-principles studies of occupancy, diffusion, and segregation of He atoms, as well as underlying evolution mechanism of He clusters in Ta, Re and Os precipitates to help to understand the effect of alloying solutes on He retention and bubble formation. It is found that single He atom prefers tetrahedral (T) site in Ta and basal octahedral (BO) site in Re and Os. Single He atom prefers the diffusion path from one T site to the closest T site in Ta, and the diffusion path from one BO site to the next BO site passing an octahedral site along $\langle$0001$\rangle$ direction in Re and Os. The diffusion of single He atom in Ta, Re and Os is relatively difficult than that in W. He atoms are energetically favorable to segregate at interstitial sites forming He$_{n}$ clusters in Ta, Re and Os, and form close-packed He monolayer structure between (110) planes in Ta. The binding strength of He$_{n}$ cluster in Ta, Re and Os is relatively small than that in W (W>Os>Re>Ta). Compared with interstitial sites, He atoms are more energetically favorable to aggregate in vacancy cluster forming VacmHen. The binding strength order of VacmHen cluster in the systems obeys W>Os>Re>Ta. We thus expect that the presence of Ta and Re may contribute to reduce He retention and bubble formation in W.

submitted time 2017-08-23 Hits1102Downloads668 Comment 0

2. chinaXiv:201703.01044 [pdf]

Heat Capacity and Thermal Expansion of Water and Helium

N. M. Putintsev; D. N. Putintsev
Subjects: Dynamic and Electric Engineering >> Engineering Thermophysics

Original expressions for heat capacity CV and its components, vibrational and configurational components of thermal expansion coefficient were established. The values of CV, Cvib, Cconf, ?vib and ?conf for water and helium 4He were calculated.

submitted time 2017-03-31 From cooperative journals:《热科学学报》 Hits1442Downloads545 Comment 0

3. chinaXiv:201703.00583 [pdf]

Detection of helium in irradiated Fe9Cr alloys by coincidence Doppler broadening of slow positron annihilation

Xingzhong Cao; Te Zhu; Shuoxue Jin; Peng Kuang; Peng Zhang; Eryang Lu; Yihao Gong; Liping Guo; Baoyi Wang
Subjects: Physics >> Condensed Matter: Structural, Mechanical and Thermal Properties

An element analysis method, coincidence Doppler broadening spectroscopy of slow positron annihilation, was employed to detect helium in ion irradiated Fe9Cr alloys. Spectra with higher peak to background ratio were recorded using a two-HPGe-detector coincidence measuring system. It means that information in the high-momentum area of the spectra can be used to identify helium in metals. This identification is not entirely dependent on the helium concentration in the specimens, but is related to the structure and microscopic arrangement of atoms surrounding the positron annihilation site. The results of Doppler broadening spectroscopy and transmission electron microscopy show that vacancies and dislocations were formed in ion irradiated specimens. Thermal helium desorption spectrometry was performed to obtain the types of He traps.

submitted time 2017-03-26 Hits2173Downloads1240 Comment 0

4. chinaXiv:201703.00580 [pdf]

Helium/hydrogen synergistic effect in reduced activation ferritic/martensitic steel investigated by slow positron beam

Te Zhu; Shuoxue Jin; Liping Guo; Yuanchao Hu; Eryang Lu; Jianping Wu; Baoyi Wang; Long Wei; Xingzhong Cao
Subjects: Physics >> Condensed Matter: Structural, Mechanical and Thermal Properties

Here, we investigated the irradiation defect in reduced activation ferritic/martensitic steels by slow positron beam. Three ion-irradiation experiments were carried out: (i) He2+ irradiation, (ii) H+ irradiation and (iii) He2+ irradiation followed by H+ irradiation, at temperature 450 oC. The presents of vacancy defects, represented by ?SHe+H parameter, induced by sequential irradiations was larger than the sum of defects, ?SHe parameter + ?SH parameter, caused by single He ions and single H ions. The synergistic effect of He and H was confirmed clearly from the perspective of positron annihilation spectroscopy.

submitted time 2017-03-26 Hits1988Downloads1145 Comment 0

5. chinaXiv:201703.00576 [pdf]

Helium retention with dislocations in deformed pure iron

Y. H. Gong; X. Z. Cao; S. X. Jin; E. Y. Lu; Y. C. Hu; T. Zhu; P. Kuang; Q. Xu; B. Y. Wang
Subjects: Physics >> Condensed Matter: Structural, Mechanical and Thermal Properties

Effects of deformed dislocation on helium retention in pure iron, including the helium atoms diffusion along the dislocation line and desorption from dislocation trapping sites, were investigated. The dislocation defect was introduced in specimens by cold-rolling, and then 5 keV helium ions were implanted into the deformed specimens. Slow positron beam technology and thermal desorption spectroscopy were used to investigate the evolution of dislocation defects and the desorption behavior of helium atoms under influence of dislocation. The behaviors of S-E, W-E and S-W plots indicate clearly that lots of helium atoms remain in the deformed specimen and helium atoms combining with dislocation change the distribution of electron density. The helium desorption plot indicates that dislocation accelerates helium desorption at 293 K-600 K and facilitates helium dissociation from HenVm (n/m=1.8) cluster.

submitted time 2017-03-26 Hits1397Downloads818 Comment 0

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