最新刊期
卷 0 ， 期 0 ， 2020
- 摘要：第三届“王淦昌优秀核科学和核技术论文奖”评定揭晓第三届“王淦昌优秀核科学和核技术论文奖”是评选１９９４－１９９５年两年内发表在《核技术》和《ＮｕｃｌｅａｒＳｃｉｅｎｃｅａｎｄＴｅｃｈｎｉｑｕｅｓ》上的优秀论文。经全体评委初评及评委常委复评。再经评委主...
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发布时间：2021-04-09 - 摘要：The DZ17G alloys with different P contents have been studied by the positron lifetime spectroscopy. lt is found that there are a decrease in electron density, an increase in defect concentration and a decline in the mechanical properties for the alloy with P≥ 0.03wt%, but When P< 0.016wt%, no obvious changes in the three aspects are observed. Therefore , to keep P<0.015wt% is important for DZ17G alloy to have good mechanical properties.关键词：Positron lifetime spectra;Superalloy;Phosphorus
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发布时间：2021-04-09 - 摘要：A program of Monte Carlo simulation has been designed to study the positron transport in GaAs. The influences of effective mass, impurity concentration and temperature on positron mobility have been discussed.关键词：Positron mobility;Monte Carlo simulation;GaAs
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发布时间：2021-04-09 - 摘要：Relationship between size or concentration of free-volume cavities in P（MAMMA）/ladderlike PPSQ blends and the composition was studied by the positron annihilation technique. Curves of positron lifetime vs. temperature for the blends with two different composition indicate that there are two structural transitions, Tβ and Tg and that Tβ and T g for sample C5 （5%PPSQ） are lower that those for Sample G1,（1%PPSQ） because Sample C5 has a greater free- volume fraction than Sample C1. Effect of thermal history on the structure of P（MMA- MAA）/PPSQ was also investigated. It is shown that the relation of average lifetime and temperature is similar to that of free-volume fraction and temperature.关键词：PMMA-MAA)/ladderlike PPSQ;Positron lifetime;Free-volume
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发布时间：2021-04-09 - 摘要：The singlet oxygen O induced by laser in a methanol- water system with photosensitizer, methylene blue （MB）, was probed by positronium. According to the theory of positron annihilation and chemical reaction kinetics , the relation between concentration of MB and variation of positron annihilation rate caused by , was deduced. The experimental results agree with the theory, confirming the formation of 1O2 in such a photochemical reaction.关键词：Positronium;Laser inducement;Singlet oxygen;Photosensitizer;Methylene blue
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发布时间：2021-04-09 - 摘要：The positron annihilation lifetime spectra of unirradiated and gamma- ray irradiated thermoluminesecent materials LiF:Mg,Ti and LiF:Mg, Cu,P and MgSO4 have been decomposed into three components. The for the heavily doped LiF samples are very similar, which implies that the positive ion vacancies have less effect on the spectra. lt is observed that 2 alters slightly but oppositely with dose in a dose range from 0.05 to 1kGy. lsochronal annealing of the irradiated MgSO4 samples indicates that the and may be related to R radicals（where R represents SO42￣, SO4￣ and SO3￣ ）, and their intensities I and I3 are probably dependent on the formed （Mg2+ vacancy-R） complexes and their competition.关键词：Thermoluminescence;F center;Quasi- positronium
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发布时间：2021-04-09 - 摘要：The positron lifetime spectra of directional graphite and nanocrystalline carbon have been measured. Two kinds of microdefect were found in the nanocrystalline carbon prepared by the heat- dissolve method:free volumes （with a size smaller than that of a monovacancy） and microvoids （with a size of about ten monovacancies）. The lifetimes measured , and the corresponding interfacial defects in the samples are discussed in comparison with the nanocrystalline iron and TiO2 materials, prepared by " compacting ultrafine powders" method and the nanocrystalline NiP material prepared by the crystallization method.关键词：Nanocrystalline carbon;Positron lifetime;Microdefects
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发布时间：2021-04-09 -
Structural instability study of a Bi-based superconductorby the positron lifetime spectrum technique
摘要：The variations of positron lifetimes with time at room temperature were measured for the Bi- based 2212 phase superconductor. lt is found that lifetimes and , intensity I1, mean lifetime and bulk lifetime all keep on decreasing for 130 days, and then remain roughly unchanged. This result confirms that the structure of oxide superconductors is instable even at room temperature. The decrease of the annihilation parameters with time is explained in terms of the intercalation of the excess oxygen in the region between the Bi-O layers. Possible correlations with the electron structure, oxygen content, hole density and transition temperature are also discussed.关键词：Bi- based superconductors;Positron lifetime;Structural instability- 8
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发布时间：2021-04-09 - 摘要：Defects in the Si- doped, N- type HB GaAs single cryatal irradiated by En≥1MeV fission neutrons with a fluence of 6.5 × 1015/cm2 and 1.4 × 1014/cm2 respectively have been investigated using the positron annihilation lifetime technique. The mono- and di- vacancies were created by the irradiation and the tri- vacancies were formed during annealing. The concentration of, defects was proportional to the irradiating neutron fluence . Three annealing stages were observed at 250, 450 and 650℃ corresponding to the mono-, di-and tri-vacancies, respectively.关键词：GaAs;Fission fast neutron irradiation;Defects;Annealing;Positron annihilation
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发布时间：2021-04-09 - 摘要：By using a pulsed low energy positron lifetime system, the positron lifetime spectra were measured of the high- temperature superconducting epitaxial thin film YBa2Cu3O7-x samples prepared by the pulsed laser deposition （PLD）, magnetron- sputtering method and evaporation method, respectively. It is found that besides shallow positron trapping centers there ace a number of deep trapping centers which the bulk material lacks. At low temperature the deep trapping centers have a tendency to enlarge. The relationship between positron lifetime and the deposition conditions （substrate temperature and partial air pressure） of the PLD films indicates that the defect type is independent of the deposition conditions and the defect concentration increases with decreasing substrate temperature or rising partial air pressure.关键词：The high temperature superconducting epitaxial thin film;Defects;Low energy positron lifetime spectrum
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发布时间：2021-04-09 - 摘要：Studies on high temperature properties of metals and alloys by using positron annihilation technique ,are briefly reviewed. The principle and applications of the β-Y positrorn lifetime systems are emphatically discussed, and the further development of this field is simply introduced.关键词：Thermal equilibrium measurement;β - Y positron lifetime spectrometer;Metal;Alloy
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发布时间：2021-04-09 - 摘要：The dependences of positron lifetime and intensity on calcination temperature and coating quantity for the TiO2/mica pearly pigment were studied, and the results were compared with those of X-ray diffraction and SEM.关键词：Positron annihilation;Lifetime;Pearly pigments
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发布时间：2021-04-09 - 摘要：The positron annihilation lifetime technique has been used to study the radiation damages in N-type HB GaAs single crystal induced by 5 .0MeV and 9.5MeV fast neutron irradiations. lt was shown that the 1013n/cm2 irradiation created mono-and di- vacancies while the 1011- 1012 n/cm2 irradiation produced mono-vacancies only Moreover, the higher the neutron energy and fluence, the higher the concentration of the produced defects, and the production rate of defects is more sensitive to fluence than to energy. The annealing behavior of defects was also investigated up to 750℃. Tri- vacancies were formed between 450℃ and 620℃ in GaAs irradiated by 9.5MeV neutrons with a fluence of 1013n/cm2.
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发布时间：2021-04-09 - 摘要：The effect of positron irradiation on photoluminescence（PL） of porous silicon has been studied. After four hour positron irradiation, the red PL spectrum of porous silicon blueshifts into greenish spectral region, and a higher energy luminescence band is introduced into this blueshifted spectrum The fourier transform infrared absorption experiment shows that the positron irradiation can cause further oxidization of porous silicon. A possible mechanism causing this change of PL spectra after positron irradiation is suggested.关键词：Positron annihilation;Porous silicon;Photoluminescence spectra;Hole
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发布时间：2021-04-09 - 摘要：The basic principle of the time differential perturbed angular correlation method and its application in materials science are described.关键词：Time differential perturbed angular correlation;Materials science;Application
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发布时间：2021-04-09 - 摘要：Si（100） samples were implanted with low energy As + ions at different incident angles and followed by rapid thermal annealing. The defects in Si（100） were measured by Doppler broadening of positron annihilation. The distribution of defects is solved by simulating a one dimensional diffusion equation. The density of defects produced by 15. implantation of As + is higher than that by 60° implantation, and the types of defects are different. The defects produced by 15°implantation can be eliminated effectively by rapid thermal annealing.关键词：Slow positron;Doppler broadening;Parameter S;Defect;lon implantation;Rapid thermal annealing
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发布时间：2021-04-09
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