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1. chinaXiv:201703.00628 [pdf]

Simulation of positron backscattering on Al, Cu, Ag and Au targets using GEANT4 code

Xin Lai; Xiaopan Jiang; Xingzhong Cao; Xi Zhang; Zhiming Zhang; Xuexiang Cao; Gang Xiang; Baoyi Wang; Long Wei
Subjects: Physics >> Condensed Matter: Structural, Mechanical and Thermal Properties

In this paper, backscattering of 3-50 keV positrons on Al, Cu, Ag and Au metallic targets has been systematically investigated using GEANT4 code. The dependence of positron backscattering coefficients on atomic number Z, target thickness, incident energy and angles has been discussed comprehensively. Besides, positron backscattering spectra for those metallic targets at different discrete scattering angles were also studied to provide theoretical basis of the most appropriate scattering angle selected for simulation parameters and specified applied measurement techniques. The impact of atomic number Z of targets on positron backscattering spectra was investigated as well. Simulation results are in reasonable agreement with previous experiment data and theoretical work.

submitted time 2017-03-26 Hits7845Downloads679 Comment 0

2. chinaXiv:201703.00587 [pdf]

Modification of source contribution in PALS by simulation using Geant4 code

Xia Ning; Xingzhong Cao; Chong Li; Demin Li; Peng Zhang; Yihao Gong; Rui Xia; Baoyi Wang; Long Wei
Subjects: Physics >> Condensed Matter: Structural, Mechanical and Thermal Properties

The contribution of positron source for the results of a positron annihilation lifetime spectrum (PALS) is simulated using Geant4 code. The geometrical structure of PALS measurement system is a sandwich structure: the 22Na radiation source is encapsulated by Kapton films, and the specimens are attached on the outside of the films. The probabilities of a positron being annihilated in the films, annihilated in the targets, and the effect of positrons reflected back from the specimen surface, are simulated. The probability of a positron annihilated in the film is related to the species of targets and the source film thickness. The simulation result is in reasonable agreement with the available experimental data. Thus, modification of the source contribution calculated by Geant4 is viable, and it beneficial for the analysis of the results of PALS.

submitted time 2017-03-26 Hits663Downloads410 Comment 0

3. chinaXiv:201703.00586 [pdf]

Estimation of dislocation concentration in plastically deformed FeCrNi alloy by positron annihilation lifetime

Eryang Lu; Xingzhong Cao; Shuoxue Jin; Yihao Gong; Peng Zhang; Runsheng Yu; Baoyi Wang
Subjects: Physics >> Condensed Matter: Structural, Mechanical and Thermal Properties

Dislocations would be induced after plastic deformation, which might change the mechanical properties of solids. FeCrNi austenitic model alloy and its Mo-diluted alloy were cold rolled with different degree of thickness reduction. Positrons are sensitive to point defects, which are easily trapped and annihilated around the trapping sites. The mean positron lifetimes have been used to estimate the average dislocation concentration in solids. Meanwhile, the trapping efficiency μ was calculated from the lifetime results. The trapping efficiency value is estimated about 3.31×10-7 cm3s-1 for FeCrNi alloy and 3.31×10-7 cm3s-1 for Mo-diluted alloy, respectively. The increment of the hardness value during plastic deformation is related to the increase of the dislocation density and dislocation pile up in solids.

submitted time 2017-03-26 Hits655Downloads420 Comment 0

4. chinaXiv:201703.00585 [pdf]

Irradiation induced defects by Fe-ion in 316L stainless steel studied by Positron Annihilation Spectroscopy

Xingzhong Cao; Eryang Lu; Shuoxue Jin; Yihao Gong; Yuanchao Hu; Te Zhu; Peng Zhang; Long Wei; Baoyi Wang
Subjects: Physics >> Condensed Matter: Structural, Mechanical and Thermal Properties

Solution annealed type 316L austenitic stainless steels were irradiated using 2 MeV Fe ions at room temperature. The implanted fluences were 2012 ions/cm2 and 1013 ions/cm2, respectively. Variable mono-energetic positron beam was performed to characterize the evolution of microstructure and irradiation induced defects. Results show that large amount of vacancy defects formed after heavy ion irradiation. In which, some of mono-vacancies might migrate to form small-sized clusters at room temperature. After irradiation, implanted Fe atoms mainly be interstitials atoms, but some Fe atoms might recombine with vacancies due to their high mobility, which could decrease the defect concentration, effectively.

submitted time 2017-03-26 Hits664Downloads394 Comment 0

5. 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 Hits554Downloads353 Comment 0

6. chinaXiv:201703.00581 [pdf]

Probing sub-nano level molecular packing and correlated positron annihilation characteristics in ionic cross-linked Chitosan membrane using Positron Annihilation Spectroscopy

Rui Xi; Xingzhong Cao; Meizhen Gao; Peng Zhang; Minfeng Zeng; Baoyi Wang; Long Wei
Subjects: Physics >> Condensed Matter: Structural, Mechanical and Thermal Properties

Chitosan, CS, cross-linked with bivalent palladium has shown enhanced mechanical and thermal properties depending on the transformation of the structure at a microscopic scale. In the present study, CS directly cross-linked by palladium cation membranes (CS-cr-PM) were prepared through solution-casting method. The motion of chitosan chains was great suppressed after crosslinking, making a great reduce of swelling ratio by a water-swelling degree measurement, which led to molecular chain rigidity to be improvement. In order to investigate the chain packing at the molecular level in the ionic cross-linked CS system, the structure of chemically-crosslinked CS is investigated by means of the combined use of wide angle X-ray diffraction (WAXD), Infrared measurements, and a combination of positron annihilation lifetime spectroscopy (PALS) and simultaneous coincidence Doppler broadening (CDB) spectroscopy offers coherent information on both the free-volume related sub-nano level molecular packing and the chemical surrounding of free volume nanoholes in CS-cr-PM as a function of palladium salt loading. The variations in free volume size and size distribution have been determined through the ortho-positroium (o-Ps) lifetime and its lifetime distribution. The studies showed that strong interaction between CS molecules and palladium cations results in the change of crystallinity in formed CS-cr-PM leading to variational chain packing density. Meanwhile, significant inhibition effects on positronium formation due to doping are observed, which could be interpreted in terms of the existence of chlorid ion. Applications of positron annihilation spectroscopy to study the microstructure and correlated positron annihilation characteristics in ionic cross-linked CS system are systematic discussed.

submitted time 2017-03-26 Hits587Downloads376 Comment 0

7. 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 Hits574Downloads348 Comment 0

8. chinaXiv:201703.00575 [pdf]

Effect of annealing on Cu precipitates in H ion irradiated Fe–0.6%Cu studied by positron annihilation

Shuoxue Jin; Peng Zhang; Eryang Lu; Baoyi Wang; Daqing Yuan; Long Wei; Xingzhong Cao
Subjects: Physics >> Condensed Matter: Structural, Mechanical and Thermal Properties

Fe–0.6%Cu alloy was irradiated with H ions to 0.1 dpa, and then annealed for 30 min from 150 oC to 500 oC. We focused the evolution of Cu precipitates in irradiated Fe–0.6%Cu alloy after the isochronal annealing from the perspective of positron annihilation. The ΔW parameters after thermal annealing (400 oC and 500 oC) were much larger than that induced by 0.1 dpa H irradiation. Annealing could promote the aggregation of the Cu-vacancy complexes, and form the Cu cluster–vacancies complexes. When the vacancy-like defects recovered around 500 oC, it meant the formation and growing of the defect-free Cu precipitates.

submitted time 2017-03-26 Hits596Downloads338 Comment 0

9. chinaXiv:201703.00573 [pdf]

Correlation between Cu precipitates and irradiation defects in Fe-Cu model alloys investigated by Positron annihilation spectroscopy

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

The correlation between Cu precipitates and vacancy-like defects in three Fe-Cu model alloys, Fe-0.15%Cu, Fe-0.3%Cu and Fe-0.6%Cu, irradiated at 400 °C with hydrogen ions at doses from 0.045 to 0.45 dpa, were revealed by positron annihilation spectroscopy. The formation of vacancy-like defects surrounded by tiny Cu precipitates induced the increment of the S and W parameters after irradiation. The peak value of the relative W parameter (ΔW/W), as the high momentum information on Cu precipitates, located in the track region and decreased with irradiation dose increased from 0.045 dpa to 0.45 dpa. The information on high momentum depended on the coverage fraction of the defects by Cu atoms. The effect of the irradiation dose, the irradiation depth and the Cu content on the Cu coverage fraction of the defects has been investigated in the present work

submitted time 2017-03-26 Hits555Downloads346 Comment 0

10. chinaXiv:201703.00571 [pdf]

Investigation of vacancy-type defects in helium irradiated FeCrNi alloy by slow positron beam

Eryang Lu; Xingzhong Cao; Shuoxue Jin; Peng Zhang; Chunxiong Zhang; Jing Yang; Yaru Wu; Liping Guo; Baoyi Wang;
Subjects: Physics >> Condensed Matter: Structural, Mechanical and Thermal Properties

The evolution of microstruture for Fe16.7Cr14.5Ni model alloy and 316 stainless steel irradiated with 140 keV He ions were studied by Positron annihilation spectroscopy. The fluences were 1016 and 5016 He ions/cm2. The irradiation temperature was room temperature and 573 K, respectively. The variation of S parameter-incident positron energy profile indicated that large amount of vacancy-type defects formed after He ion irradiation. Meanwhile, helium atoms deposited in bulk and certain amount of He-vacancy complexes were formed. The vacancy-type defects could be the major defects in track region and He-vacancy complexes would be the main defects in cascade region. The vacancy-type defects could migrate and aggregate to form vacancy clusters and even microvoids at elevated temperature irradiation. The diffusion mechanism of helium atoms might be changed at different irradiation temperature.

submitted time 2017-03-26 Hits585Downloads384 Comment 0

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