Subjects: Physics >> Nuclear Physics submitted time 2023-06-18 Cooperative journals: 《Nuclear Science and Techniques》
Abstract： The positron annihilation lifetime (PAL) technique has been applied to study the effects of gamma-ray irradiation on polymer materials, such as ethylene propylene diene monomer (EPDM), nitrile butadiene rubber (NBR), and chloroprene rubber (CR), used in various industries. PAL measurements were performed with a conventional fast-fast coincidence system. Polymer materials were irradiated with 25 Gy/h in three conditions (50, 100, 500 Gy) and 5 kGy/h in six conditions (5, 50, 200, 500, 800, and 1 000 kGy) at room temperature with a 60Co gamma-ray source. Afterwards, the irradiated samples were measured by PAL spectroscopy. The delayed lifetime spectra of irradiated and unirradiated samples were decomposed into three lifetime components. The lifetime parameters indicate the free-volume size and concentration. The longest lifetime component represents the free volume size in polymer. Free volume and intensity were multiplied as a measure of relative fraction of free-volume hole. Cross-linking and degradation could occur when a polymer is irradiated. The free volumes of polymers were decreased accordingly. These results were verified through PAL measurement. From the Tao-Eldrup model, the mean radius and free volume fraction of CR, EPDM, and NBR were calculated. We certified the decrease of the fractional free volume. From these results, this study verified the feasibility of PA application on polymers.
Subjects: Physics >> Condensed Matter: Structural, Mechanical and Thermal Properties submitted time 2017-03-26
Abstract：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.
Peer Review Status:
Awaiting Review
Subjects: Physics >> Condensed Matter: Structural, Mechanical and Thermal Properties submitted time 2017-03-26
HU Yuan-Chao
CAO Xing-Zhong
ZHANG Peng
TSUCHIDA Hidetsugu
XU Qiu
JIN Shuo-Xue
LU Er-Yang
LI Yu-Xiao
YU Run-Sheng
WANG Bao-Yi
WEI Long
Abstract：Thermal aging effects on surface of 2.5 MeV Fe ion irradiated Fe-0.6%Cu alloy were investigated using positron annihilation techniques. The samples were irradiated at 573 K to a dose of 0.1 dpa. Their thermal aging was performed at 573 K for 5, 50, and 100 h. From the results of Doppler broadening measurement, an obvious trough could be seen in near surface region from the S parameters and inflection point form at S-W curves. This indicates changes in the annihilation mechanism of positrons in surface region after thermal aging. Coincident Doppler broadening indicates that the density of Cu precipitates in the thermal aged samples decreased, due to recovery of the vacancies. Keywords Fe-Cu alloy; Positron annihilation; Irradiation; Thermal aging
Peer Review Status:Awaiting Review
Subjects: Physics >> Condensed Matter: Structural, Mechanical and Thermal Properties submitted time 2017-03-26
Abstract：Cu precipitates played a key factor in irradiation induced hardening and embrittlement of reactor pressure vessel (RPV).In this work, two kinds of Fe-Cu model alloys with different Cu contents irradiated by Fe ion at 573 K were investigated using positron annihilation techniques and SEM. Doppler Broadening Spectroscopy(DBS) results indicated that with the irradiation dose increased from 0.1 dpa to 1.2 dpa, more vacancy-type defects were induced during Fe ion irradiation, and with different Cu contents, defects condition had few changes. Coincident Doppler Broadening (CDB) results indicated Cu precipitates were formed during the irradiation, which could be verified through the SEM results. The CDB results also showed that the Cu precipitates were the same at 0.1 dpa between the samples with different Cu contents. In Fe0.6Cu samples, more Cu precipitates were formed than that of Fe0.3Cu sample at 1.2 dpa.
Peer Review Status:Awaiting Review
Subjects: Physics >> Condensed Matter: Structural, Mechanical and Thermal Properties submitted time 2017-03-26
Abstract：The effect of Cu content on the evolution of defects in Fe-x%Cu alloys (x= 0.15, 0.3, and 0.6) were investigated using Positron Annihilation Lifetime Spectroscopy. The vacancy-type and Cu-vacancy complexes defects were respectively produced by quenching from 1173 K and cold-rolled deformation followed by isochronal annealing. The isochronal annealing results obtained by PALS showed that Cu-vacancy complexes delayed the complete recovery of vacancy-type defects and the complete recovery temperature increased with the content of Cu in 30% deformed Fe-Cu alloys. The increment of Cu content also restrained the migration of vacancies in as-quenched Fe-Cu alloys.
Peer Review Status:Awaiting Review
Subjects: Physics >> Condensed Matter: Structural, Mechanical and Thermal Properties submitted time 2017-03-26
Abstract：Abstract. The microstructural features and the effect of Mo addition in FeCrNi austenitic alloy during incubation period were investigated using positron annihilation technique and micro-Vickers Hardness. The electron irradiation, which could induce vacancy defects in material, was performed at room temperature up to the dose of 1.70-4 and 50-4 dpa, respectively. The defect concentration was estimated about 10-4-10-7 though the standard trapping model. The added Mo atoms could trap vacancies to form Mo-vacancy complexes, which may restrain the migration and growth of vacancy defects during electron irradiation. In addition, the microstructural evolution during electron radiation resulted in hardening, while the added Mo might improve the hardening property of the alloy.
Peer Review Status:Awaiting Review
Subjects: Physics >> Nuclear Physics submitted time 2016-09-13
Abstract： With the recently emerging global interest in building a next generation of circular electron-positron colliders to study the properties of the Higgs boson, and other important topics in particle physics at ultra-high beam energies, it is also important to pursue the possibility of implementing polarized beams at this energy scale. It is therefore necessary to set up simulation tools to evaluate the beam polarization at these ultra-high beam energies. In this paper, a Monte-Carlo simulation of the equilibrium beam polarization based on the Polymorphic Tracking Code(PTC) (Schmidt et al., 2002 [1]) is described. The simulations are for a model storage ring with parameters similar to those of proposed circular colliders in this energy range, and they are compared with the suggestion (Derbenev et al., 1978 [2]) that there are different regimes for the spin dynamics underlying the polarization of a beam in the presence of synchrotron radiation at ultra-high beam energies. In particular, it has been suggested that the so-called "correlated" crossing of spin resonances during synchrotron oscillations at current energies, evolves into "uncorrelated" crossing of spin resonances at ultra-high energies.
Peer Review Status:Awaiting Review
Subjects: Nuclear Science and Technology >> Radiation Physics and Technology submitted time 2024-08-22
Hong-Xia Xu
Jian-Dang Liu
Bang-Jiao Ye
Zi-Wen Pan
Jun Lin
Jin-Liang Song
Jian-Qing Cao
Chao Yan
Ying-Ping Hao
Jin-Xing Cheng
Qing-Bo Wang
Abstract： The stability of matrix graphite under neutron irradiation and in corrosive environments is crucial for the
safe operation of molten salt reactors (MSRs). Raman spectroscopy and a slow positron beam were employed
to investigate the effects of He ion irradiation fluences and subsequent annealing on the microstructure and
defects of the matrix graphite. He ions with 500 keV energy and fluences ranging from 1.1 × 1015 ions/cm2
to 3.5 × 1017 ions/cm2 were used to simulate neutron irradiation at 300K. The samples with an irradiation
fluence of 3.5×1016 ions/cm2 were subjected to isochronal annealing at different temperatures (573K, 873 and
1173K) for 3 h. The Raman results revealed that the D peak gradually increased, whereas the intrinsic G peak
decreased with increasing irradiation fluence. At the same irradiation fluence, the D peak gradually decreased,
whereas the intrinsic G peak increased with increasing annealing temperature. Slow positron beam analysis
demonstrated that the density or size of irradiation defects (vacancy type) increased with higher irradiation
fluence, but decreased rapidly with increasing annealing temperature. The Raman spectral analysis of sample
cross sections subjected to high irradiation fluences revealed the emergence of amorphization precisely at the
depth where ion damage was most pronounced, whereas the surface retained its crystalline structure. Raman
and positron annihilation analyses indicated that the matrix graphite exhibited good irradiation resistance to He
ions at 300K. However, vacancy-type defects induced by He ion irradiation exhibit poor thermal stability and
can be easily removed during annealing.
Peer Review Status:Awaiting Review
Subjects: Physics >> Condensed Matter: Structural, Mechanical and Thermal Properties submitted time 2017-03-26
Xin Lai
Xiaopan Jiang
Xingzhong Cao
Xi Zhang
Zhiming Zhang
Xuexiang Cao
Gang Xiang
Baoyi Wang
Long Wei
Abstract：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.
Peer Review Status:Awaiting Review
Subjects: Physics >> Condensed Matter: Structural, Mechanical and Thermal Properties submitted time 2017-03-26
Abstract：The microstructural features and the effect of Mo addition during incubation period in FeCrNi austenitic alloy were investigated using positron annihilation technique and micro-Vickers Hardness. The electron irradiation, which could induce vacancy defects in material, was performed at room temperature up to the dose of 1.70-4 and 50-4 dpa, respectively. The defect concentration was estimated about 10-4-10-7 though standard trapping model. The added Mo could trap vacancies to form Mo-vacancy complexes, which may suppress the migration and growth of vacancy defects during electron irradiation. In addition, the microstructural evolution during electron radiation resulted in hardening, while the added Mo might to improve the hardening property of the alloy.
Peer Review Status:Awaiting Review
Subjects: Physics >> Nuclear Physics submitted time 2016-09-10
Abstract： We present an extraction of azimuthal correlations between two pairs of charged pions detected in opposite jets from electron-positron annihilation. These correlations may arise from the dependence of the di-pion fragmentation on the polarization of the parent quark in the process e+e−→qq¯. Due to the correlation of the quark polarizations, the cross-section of di-pion pair production, in which the pion pairs are detected in opposite jets in a dijet event, exhibits a modulation in the azimuthal angles of the planes containing the hadron pairs with respect to the production plane. The measurement of this modulation allows access to combinations of fragmentation functions that are sensitive to the quark's transverse polarization and helicity. Within our uncertainties we do not observe a significant signal from the previously unmeasured helicity dependent fragmentation function G⊥1. This measurement uses a dataset of 938~fb−1 collected by the Belle experiment at or near s√≈10.58 GeV.
Peer Review Status:Awaiting Review
Subjects: Nuclear Science and Technology >> Radiation Physics and Technology submitted time 2024-04-07
Abstract： Room-temperature ferromagnetism is observed in the O+-implanted AlN films with O+ doses of 5 × 1016 cm-2 (AlN:O5×1016) and 2 × 1017 cm-2 (AlN:O2×1017). The observed magnetic anisotropy indicate that the ferromagnetism is attributed to the intrinsic properties of O+-implanted AlN films. The out-of-plane saturation magnetization (MS) of the AlN:O5×1016 is about 0.68 emu/g, much higher than that of AlN:O2×1017, 0.09 emu/g, which is due to the excessively high O+ dose made more O+ ions occupy adjacent Al3+ positions in forms of antiferromagnetic coupling. Doppler broadening of positron annihilation radiation measurements demonstrate the existence of Al vacancies in the O+-implanted AlN films. The first-principles calculations suggest that the ferromagnetism originates mainly from the Al vacancies. Meanwhile,the formation of divacancies or vacancy clusters by high concentrations of Al vacancies will lead to the transformation of VAl–VAl coupling from ferromagnetim to antiferromagnetimm, ultimately weakening the ferromagnetism of the sample.
Subjects: Physics >> Condensed Matter: Structural, Mechanical and Thermal Properties submitted time 2017-03-26
Abstract：Positron irradiation effects on positronium formation in low-density polyethylene (LDPE), gamma-irradiated LDPE and unplasticized PVC (UPVC) are studied. At least in one of the three different measurements, i.e., prolonged positron annihilation measurement at room temperature, low temperature in darkness and subsequent measurement under light, changes in o-Ps intensity are observed in nonirradiated LDPE and gamma-irradiated LDPE. While in UPVC, change in o-Ps intensity is hardly observable in all the above-mentioned three measurements. Reduction of o-Ps intensity by light indicates that positronium formation via the recombination of a positron and a trapped electron exists in LDPE and gamma-irradiated LDPE. The absence of light bleaching effect, together with the fact that the value of o-Ps intensity in heating and cooling process of a thermal circle is nearly the same, indicates that in UPVC, positronium can not be formed through trapped electron mechanism. This study highlights the speciality of positronium formation in UPVC, positronium is formed exclusively by the recombination of electron-positron pairs with short separations.
Peer Review Status:Awaiting Review
Subjects: Physics >> Condensed Matter: Structural, Mechanical and Thermal Properties submitted time 2017-03-26
Abstract：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.
Peer Review Status:Awaiting Review
Subjects: Physics >> Nuclear Physics submitted time 2016-09-14
Abstract： We study the collider phenomenology of the electroweak phase transition and electroweak baryogenesis in the framework of the effective field theory. Our study shows that the effective theory using the dimension-6 operators can enforce strong first order phase transition and provide sizable CP violation to realize a successful electroweak baryogenesis. Such dimension-6 operators can induce interesting Higgs phenomenology that can be verified at colliders such as the LHC and the planning CEPC. We then demonstrate that this effective theory can originate from vector-like quarks and the triplet Higgs.
Peer Review Status:Awaiting Review
Subjects: Physics >> Nuclear Physics submitted time 2025-05-08
Abstract： In the BESIII detector at Beijing electron-positron collider, billions of events from e+e− collisions are recorded. These events passing through the trigger system are saved in raw data format files. They play an important role in the study of physics at τ -charm energy region. Here, we publish an e+e− collision dataset containing both Monte Carlo simulation samples and real data collected by the BESIII detector. The data passes through the detector trigger system, file format conversion, physics information extraction, and finally saves the physics information and detector response in text format files. This dataset is publicly available and is intended to provide interested scientists and those outside of the BESIII collaboration with event information from BE- SIII that can be used in understanding the physics research in e+e− collisions, developing visualization projects for physics education, public outreach, and science advocacy.
Peer Review Status:Awaiting Review
Subjects: Physics >> Condensed Matter: Structural, Mechanical and Thermal Properties submitted time 2017-03-26
Abstract：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.
Peer Review Status:Awaiting Review
Subjects: Physics >> Condensed Matter: Structural, Mechanical and Thermal Properties submitted time 2017-03-26
Eryang Lu
Xingzhong Cao
Shuoxue Jin
Peng Zhang
Chunxiong Zhang
Jing Yang
Yaru Wu
Liping Guo
Baoyi Wang
Abstract：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.
Peer Review Status:Awaiting Review
Subjects: Physics >> Condensed Matter: Structural, Mechanical and Thermal Properties submitted time 2017-03-26
Abstract：The formation of Cu precipitates in Fe-0.3%Cu binary model alloy after hydrogen ion irradiation at 400 was investigated by positron annihilation spectroscopy based on slow positron beam. In order to study the effect of elevated temperature for the Cu precipitates, the annealing treatment at 400 in Fe-0.3%Cu alloy was also investigated. The S-parameters of specimens increased with the irradiation dose increased, especially in the damage peak region. H+ implantation produced a large number of vacancy-type defects in Fe-0.3%Cu alloy. Compared to the unirradiated samples, the irradiated specimens show an overall major increase in W parameter values. Experimental results indicate that Cu precipitates formed easily under lower irradiation dose at elevated temperature. No obvious Cu precipitates formed when Fe-0.3%Cu alloy was annealed for 2h at 400 .
Peer Review Status:Awaiting Review
Subjects: Physics >> Condensed Matter: Structural, Mechanical and Thermal Properties submitted time 2017-03-26
M. H. Cui
Z. G. Wang
L. L. Pang
T. L. Shen
C. F. Yao
B. S. Li
J. Y. Li
X. Z. Cao
P. Zhang
J. R. Sun
Y. B. Zhu
Y. F. Li
Y. B. Sheng
Abstract：Tungsten has been selected as one of the potential candidate materials to cover some parts of the divertor in the future International Thermonuclear Experimental Reactor (ITER). The accumulation of defects and He induced by neutron irradiation and their impact on the mechanical properties of tungsten are of very importance. In this work, the high pure polycrystalline tungsten samples were implanted by 200 keV He+ with a fluence of 5016 He+/cm2 at temperatures of room temperature(RT), 200, 400 and 800oC. Vacancy-type defects were detected in all implanted samples by means of positron annihilation spectroscopy. Vacancy-type defects produced by He implantation exist in the damaged layer and are decorated by He atoms. With increasing implantation temperature, more He atoms fill in the vacancy-type defects and make for the formation of larger defects. The nano-hardness values were measured by nano-indentation technique. It is observed that implantation hardening occurred for all the implanted samples. With increasing implantation temperature from 200 to 800 oC, the change of the average hardness values which are lower than the value at RT has a tendency of enhancement for the shallower layer and degradation for the deeper layer. The hardness variations are discussed to be the pinning effects of the defects with different density or size.
Peer Review Status:Awaiting Review
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