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We provide a non-perturbative expression for the hadron production in electron-positron annihilation at zero temperature in a strongly coupled, large-Nc SU(Nc) field theory with Nf < < Nc quark flavors. The resulting expressions are valid to leading order in the electromagnetic coupling constant but non-perturbatively in the SU(Nc) interactions and the mass of the quark. We obtain this quantity by computing the imaginary part of the hadronic vacuum polarization function Pi_q using holographic techniques, providing an alternative to the known method that uses the spectrum of infinitely stable mesons determined by the normalizable modes of the appropriated fields in the bulk. Our result exhibits a structure of poles localized at specific real values of q^2, which coincide with the ones found using the normalizable modes, and extends it offering the unique analytic continuation of this distribution to a function defined for values of q^2 over the complex plane. This analytic continuation permits to include a finite decay width for the mesons. By comparison with experimental data we find qualitatively good agreement on the shape of the first pole, when using the rho meson parameters and choosing a proper normalization factor. We then estimate the contribution to the anomalous magnetic moment of the muon finding an agreement within 25%, for this choice of parameters.

The process $e^+e^- \to \pi^0\rho$ is described in the framework of the expanded NJL model in the energy region from 0.9 GeV to 1.5 GeV. The contribution of intermediate state with vector mesons $\omega(782), \,\,\phi(1020)$, and $\omega'(1420)$, where $\omega'$ is the first radial excitation of $\omega$ - meson was taken into account. Results obtained are in satisfactory agreement with experimental data.

The electronic structure of vanadium measured by Angular Correlation of electron-positron Annihilation Radiation (ACAR) is compared with the predictions of the combined Density Functional and Dynamical Mean-Field Theory (DMFT). Reconstructing the momentum density from five 2D projections we were able to determine the full Fermi surface and found excellent agreement with the DMFT calculations. In particular, we show that the local, dynamic self-energy corrections contribute to the anisotropy of the momentum density and need to be included to explain the experimental results.

Fragmentation functions are determined for the pion and kaon by global analyses of charged-hadron production data in electron-positron annihilation. Accurate measurements were reported by the Belle and BaBar collaborations for the fragmentation functions at the center-of-mass energies of 10.52 GeV and 10.54 GeV, respectively, at the KEK and SLAC B factories, whereas other available $e^+e^-$ measurements were mostly done at higher energies, mainly at the $Z$ mass of 91.2 GeV. There is a possibility that gluon fragmentation functions, as well as quark fragmentation functions, are accurately determined by scaling violation. We report our global analysis of the fragmentation functions especially to show impacts of the B-factory measurements on the fragmentation function determination. Our results indicate that the fragmentation functions are determined more accurately not only by the scaling violation but also by high-statistical nature of the Belle and BaBar data. However, there are some tensions between the Belle and BaBar data in comparison with previous measurements. We also explain how the flavor dependence of quark fragmentation functions and the gluon function are separated by using measurements at different $Q^2$ values. In particular, the electric and weak changes are different depending on the quark type, so that a light-quark flavor separation also became possible in principle due to the precise data at both $\sqrt{s}\simeq 10.5$ GeV and 91.2 GeV.

Annihilation momentum densities and correlation enhancement factors for low-energy positron annihilation on valence and core electrons of noble-gas atoms are calculated using many-body theory. s, p and d-wave positrons of momenta up to the positronium-formation threshold of the atom are considered. The enhancement factors parametrize the effects of short-range electron-positron correlations which increase the annihilation probability beyond the independent-particle approximation. For all positron partial waves and electron subshells, the enhancement factors are found to be relatively insensitive to the positron momentum. The enhancement factors for the core electron orbitals are also independent of the positron angular momentum. The largest enhancement factor ($\sim 15$) is found for the 5p orbital in Xe, while the values for the core orbitals are typically $\sim 1.5$.

During its first year in orbit the INTEGRAL observatory performed deep exposures of the Galactic Center region and scanning observations of the Galactic plane. We report on the status of our analysis of the positron annihilation radiation from the 4th Galactic quadrant with the spectrometer SPI, focusing on the sky distribution of the 511 keV line emission. The analysis methods are described; current constraints and limits on the Galactic bulge emission and the bulge-to-disk ratio are presented.

Experimental data on the total cross section of $e^+ e^-$ annihilation into hadrons are confronted with QCD and the operator product expansion using finite energy sum rules. Specifically, the power corrections in the operator product expansion, i.e. the vacuum condensates, of dimension $d = 2$, 4 and 6 are determined using recent isospin $I=0+1$ data sets. Reasonably stable results are obtained which are compatible within errors with values from $\tau$-decay. However, the rather large data uncertainties, together with the current value of the strong coupling constant, lead to very large errors in the condensates. It also appears that the separation into isovector and isoscalar pieces introduces additional uncertainties and errors. In contrast, the high precision $\tau$-decay data of the ALEPH collaboration in the vector channel allows for a more precise determination of the condensates. This is in spite of QCD asymptotics not quite been reached at the end of the $\tau$ spectrum. We point out that isospin violation is negligible in the integrated cross sections, unlike the case of individual channels.

We investigate positron annihilation in electron liquid as a case study for many-body theory, in particular the optimized Fermi Hypernetted Chain (FHNC-EL) method. We examine several approximation schemes and show that one has to go up to the most sophisticated implementation of the theory available at the moment in order to get annihilation rates that agree reasonably well with experimental data. Even though there is basically just one number to look at, the electron-positron pair distribution function at zero distance, it is exactly this number that dictates how the full pair distribution behaves: In most cases, it falls off monotonously towards unity as the distance increases. Cases where the electron-positron pair distribution exhibits a dip are precursors to the formation of bound electron--positron pairs. The formation of electron-positron pairs is indicated by a divergence of the FHNC-EL equations, from this we can estimate the density regime where positrons must be localized. This occurs in our calculations in the range 9.4

$P$-wave coupled channel effects arising from the $D\bar{D}$, $D\bar{D}^*+c.c.$, and $D^*\bar{D}^*$ thresholds in $e^+e^-$ annihilations are systematically studied. We provide an exploratory study by solving the Lippmann-Schwinger equation with short-ranged contact potentials obtained in the heavy quark limit. These contact potentials can be extracted from the $P$-wave interactions in the $e^+e^-$ annihilations, and then be employed to investigate possible isosinglet $P$-wave hadronic molecules. In particular, such an investigation may provide information about exotic candidates with quantum numbers $J^{PC}=1^{-+}$. In the mass region of the $D\bar{D}$, $D\bar{D}^*+c.c.$, and $D^*\bar{D}^*$ thresholds, there are two quark model bare states, i.e. the $\psi(3770)$ and $\psi(4040)$, which are assigned as $(1^3D_1)$ and $(3^1S_1)$ states, respectively. By an overall fit of the cross sections of $e^+e^-\to D\bar{D}$, $D\bar{D}^*+c.c.$, $D^*\bar{D}^*$, we determine the physical coupling constants to each channel and extract the pole positions of the $\psi(3770)$ and $\psi(4040)$. The deviation of the ratios from that in the heavy quark spin symmetry (HQSS) limit reflects the HQSS breaking effect due to the mass splitting between the $D$ and the $D^*$. Besides the two poles, we also find a pole a few MeV above the $D\bar{D}^*+c.c.$ threshold which can be related to the so-called $G(3900)$ observed earlier by BABAR and Belle. This scenario can be further scrutinized by measuring the angular distribution in the $D^*\bar{D}^*$ channel with high luminosity experiments.

The positron excess observed by the PAMELA experiment may come from dark matter annihilation, if the annihilation cross section is large enough. We show that the dark matter annihilation scenarios to explain the positron excess may also be compatible with the discrepancy of the cosmic lithium abundances between theory and observations. The wino-like neutralino in the supersymmetric standard model is a good example for it. This scenario may be confirmed by Fermi satellite experiment.

Probing sub-nano level molecular packing and correlated positron annihilation characteristics in ionic cross-linked Chitosan membrane using Positron Annihilation Spectroscopy 作者： Rui Xi 1,2 Xingzhong Cao 2 Meizhen Gao 1 Peng Zhang 2 Minfeng Zeng 3 Baoyi Wang 2 Long Wei 2 作者单位： 1. Key Lab for Magnetism and Magnetic Materials of Ministry of Education, School of Physical Science and Technology, Lanzhou University, Lanzhou 730000, China 2. Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China 3. Zhejiang Key Laboratory of Alternative Technologies for Fine Chemicals Process, Shaoxing University, Shaoxing 312000, China. 提交时间： 2017-03-26 摘要: 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. Positron annihilation 分类： 物理学 &gt;&gt; 凝聚态:结构、力学和热性能 引用： ChinaXiv:201703.00581 (或此版本 ChinaXiv:201703.00581V1 ) doi:10.12074/201703.00581 CSTR:32003.36.ChinaXiv.201703.00581.V1 推荐引用方式： Rui Xi,Xingzhong Cao,Meizhen Gao,Peng Zhang,Minfeng Zeng,Baoyi Wang,Long Wei.(2017).Probing sub-nano level molecular packing and correlated positron annihilation characteristics in ionic cross-linked Chitosan membrane using Positron Annihilation Spectroscopy.中国科学院科技论文预发布平台.[ChinaXiv:201703.00581] 版本历史 [V1] 2017-03-26 19:36:59 ChinaXiv:201703.00581V1 下载全文

Radiative corrections due to pair production in process of electron-positron annihilation are considered. The main attention is paid to the corrections of the third order. Simultaneous emission of photons and pairs is taken into account. The leading log approximation and convolution procedure are used. Exponentiation is discussed. Theoretical uncertainty in description of higher order secondary pairs is estimated.

We consider the production of positrons in microquasars, i.e. X-ray binary systems that exhibit jets frequently, but not continuously. We estimate the production rate of positrons in microquasars, both by simple energy considerations and in the framework of various proposed models. We then evaluate the collective emissivity of the annihilation radiation produced by Galactic microquasars and we find that it might constitute a substantial contribution to the annihilation flux measured by INTEGRAL/SPI. We also discuss the possible spatial distribution of Galactic microquasars, on the basis of the (scarce) available data and the resulting morphology of the flux received on Earth. Finally, we consider nearby 'misaligned' microquasars, with jets occasionally hitting the atmosphere of the companion star; these would represent interesting point sources, for which we determine the annihilation flux and the corresponding light curve, as well as the line's spectral profile. We discuss the possibility of detection of such point sources by future instruments.

Enhanced positron annihilation on polyatomic molecules is a long-standing and complex problem. We report the results of calculations of resonant positron annihilation on methyl halides. A free parameter of our theory is the positron binding energy. A comparison with energy-resolved annihilation rates measured for CH$_3$F, CH$_3$Cl, CH$_3$Br [Barnes et al. Phys. Rev. A {\bf 74}, 012706 (2006)] shows good agreement and yields estimates of the binding energies.

Recently, Weiss et al. have demonstrated that it is possible to excite Auger transitions by annihilating core electrons using a low energy (less than 30eV) beam of positrons. This mechanism makes possible a new electron spectroscopy, Positron annihilation induced Auger Electron Spectroscopy (PAES). The probability of exciting an Auger transition is proportional to the overlap of the positron wavefunction with atomic core levels. Since the Auger electron energy provides a signature of the atomic species making the transition, PAES makes it possible to determine the overlap of the positron wavefunction with a particular element. PAES may therefore provide a means of detecting positron-atom complexes. Measurements of PAES intensities from clean and adsorbate covered Cu surfaces are presented which indicate that approx. 5 percent of positrons injected into CU at 25eV produce core annihilations that result in Auger transitions.

The electron-positron annihilation spectrum observed by SPI/INTEGRAL during deep Galactic Center region exposure is reported. The line energy (510.954$\pm$0.075 keV) is consistent with the unshifted annihilation line. The width of the annihilation line is 2.37$\pm$0.25 keV (FWHM), while the strength of the ortho-positronium continuum suggests that the dominant fraction of positrons (94$\pm$6%) form positronium before annihilation. Compared to the previous missions these deep INTEGRAL observations provide the most stringent constraints on the line energy and width. Under the assumption of an annihilation in a single-phase medium these spectral parameters can be explained by a warm $T_e\sim 7000-4~10^4$ K gas with the degree of ionization larger than a few $10^{-2}$. One of the wide-spread ISM phases - warm ($T_e \sim 8000$ K) and weakly ionized (degree of ionization $\sim$ 0.1) medium satisfies these criteria. Other single-phase solutions are also formally allowed by the data (e.g. cold, but substantially ionized ISM), but such solutions are believed to be astrophysically unimportant. The observed spectrum can also be explained by the annihilation in a multi-phase ISM. The fraction of positrons annihilating in a very hot ($T_e \ge 10^6$ K) phase is constrained to be less than $\sim$8%. Neither a moderately hot ($T_e \ge 10^5$ K) ionized medium nor a very cold ($T_e \le 10^3$ K) neutral medium can make a dominant contribution to the observed annihilation spectrum. However, a combination of cold/neutral, warm/neutral and warm/ionized phases in comparable proportions could also be consistent with the data.

We study the structures in cross sections and R ratios concerning electron-positron annihilation reactions, for open-strangeness, open-charm and open-beauty hadron-pair production, from the perspective of a recently developed production formalism. Special attention is paid to non-resonant contributions. Known, tentative, and yet unknown resonances are spotted, with estimates for their masses and widths.

Measurements of inclusive differential cross sections for charged pion and kaon production in electron-positron annihilation have been carried out at a center-of-mass energy of Q = 10.52 GeV. The measurements were performed with the Belle detector at the KEKB electron-positron collider using a data sample containing 113 million e+e- -> qqbar events, where q={u,d,s,c}. We present charge-integrated differential cross sections d\sigma_h+-/dz for h+- = pi+-, K+- as a function of the relative hadron energy z = 2*E_h / sqrt{s} from 0.2 to 0.98. The combined statistical and systematic uncertainties for pi+- (K+-) are 4% (4%) at z ~ 0.6 and 15% (24%) at z ~ 0.9. The cross sections are the first measurements of the z-dependence of pion and kaon production for z > 0.7 as well as the first precision cross section measurements at a center-of-mass energy far below the Z^0 resonance used by the experiments at LEP and SLC.

Effects of gamma-ray irradiation on free volume in polymers by positron annihilation lifetime spectroscopy 作者： Yongmin KIM 1 Jungki SHIN 2 Junhyun KWON 3 作者单位： 1. Department of Radiological Science, Catholic University of Daegu, Gyeongbuk 712-702, Republic of Korea 2. Korea Research Institute of Standards and Science, Daejeon 305-430, Republic of Korea 3. Korea Atomic Energy Research Institute, Daejeon 305-353, Republic of Korea 提交时间： 2023-06-18 摘要: 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. Positron annihilation techniques Positron lifetime Gamma-ray irradiation Polymers 期刊： Nuclear Science and Techniques 分类： 物理学 &gt;&gt; 核物理学 投稿状态： 已在期刊出版 引用： ChinaXiv:202306.00421 (或此版本 ChinaXiv:202306.00421V1 ) DOI:dx.doi.org/10.13538/j.1001-8042/nst.25.S010502 CSTR:32003.36.ChinaXiv.202306.00421.V1 推荐引用方式： Yongmin KIM,Jungki SHIN,Junhyun KWON.(2023).Effects of gamma-ray irradiation on free volume in polymers by positron annihilation lifetime spectroscopy.Nuclear Science and Techniques.doi:dx.doi.org/10.13538/j.1001-8042/nst.25.S010502 版本历史 [V1] 2023-06-18 17:37:41 ChinaXiv:202306.00421V1 下载全文

Effect of defects on magnetic properties of O+-implanted AlN films by positron annihilation spectroscopy 作者： Run YE 1 Bangjiao YE 2 作者单位： 1. School of Physics and Electronic Engineering, Yancheng Teachers University, Yancheng 224007, China 2. State Key Laboratory of Particle Detection and Electronics, University of Science and Technology of China, Hefei 230026 通讯作者： Run YE Email:[email protected] Bangjiao YE Email:[email protected] 提交时间： 2024-04-07 13:22:41 摘要: 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. positron annihilation spectroscopy ion implantation; semiconductors; ferromagnetism 来自： 叶润 期刊： 原子核物理评论 分类： 核科学技术 &gt;&gt; 辐射物理与技术 说明： 已被期刊“原子核物理评论”录用，稿号2023-CNPC66 投稿状态： 已被期刊接收 引用： ChinaXiv:202312.00232 (或此版本 ChinaXiv:202312.00232V2 ) DOI:10.12074/202312.00232V2 CSTR:32003.36.ChinaXiv.202312.00232.V2 推荐引用方式： Run YE,Bangjiao YE.(2024).Effect of defects on magnetic properties of O+-implanted AlN films by positron annihilation spectroscopy.原子核物理评论.doi:10.12074/202312.00232V1 版本历史 [V2] 2024-04-07 13:22:41 ChinaXiv:202312.00232V2 下载全文 [V1] 2023-12-19 08:37:52 ChinaXiv:202312.00232v1 查看此版本 下载全文

We compile the most recently measured and calculated cross sections for processes relevant to annihilation of positrons in solar flares and present the final evaluated cross sections. We calculate the 511 keV annihilation line spectrum and relative strength of the 3gamma continuum for each of the annihilation processes, using a Monte Carlo code that simulates the thermalization of and positronium production by MeV positrons. We calculate the thermally-averaged annihilation and positronium production rates and the positronium quenching rates. We apply the results to four specific environments (fully ionized, neutral, partially ionized and a non-LTE model of the quiet solar atmosphere), calculating the relative strengths of each process and the combined total annihilation line spectrum. The results are compared with data obtained recently from the high spectral-resolution detectors of RHESSI. We find that positron annihilation in solar flares can occur in a wide variety of environments. The cross sections presented here are also useful for evaluation of positron annihilation in other environments such as the interstellar medium.

We studied the parameters to optimize the production of negatively-charged nitrogen-vacancy color centers (NV-) in type~1b single crystal diamond using proton irradiation followed by thermal annealing under vacuum. Several samples were treated under different irradiation and annealing conditions and characterized by slow positron beam Doppler-broadening and photoluminescence (PL) spectroscopies. At high proton fluences another complex vacancy defect appears limiting the formation of NV-. Concentrations as high as 2.3 x 10^18 cm^-3 of NV- have been estimated from PL measurements. Furthermore, we inferred the trapping coefficient of positrons by NV-. This study brings insight into the production of a high concentration of NV- in diamond, which is of utmost importance in ultra-sensitive magnetometry and quantum hybrid systems applications.

The two-photon positron annihilation density matrix is found to separate into a diagonal center of energy factor implying maximally entangled momenta, and a relative factor describing decay. For unknown positron injection time, the distribution of the difference in photon arrival times is a double exponential at the para-Ps decay rate, consistent with experiment (V. D. Irby, Meas. Sci. Technol. 15, 1799 (2004)).

The two-photon positron annihilation density matrix is found to separate into a diagonal center of energy factor implying maximally entangled momenta, and a relative factor describing decay. For unknown positron injection time, the distribution of the difference in photon arrival times is a double exponential at the para-Ps decay rate, consistent with experiment (V. D. Irby, Meas. Sci. Technol. 15, 1799 (2004)).

Platinum Octaethyl Porphyrin (Pt.OEP) is an efficient phosphor under ultraviolet excitation. The phosphorescent triplet state (T(sub 1)) is readily quenched by the oxygen (O2) molecules. This phenomenon is being utilized as the basis for global air pressure measurements in aerodynamic facilities at various laboratories. The exact mechanism by which O2 molecules quench the (T(sub 1)-S(sub 0)) transitions is still unknown. The diamagnetic S(sub n) singlet states, which feed T(sub 1) states via intersystem crossings, would presumably not be affected by O2. It must be the magnetic T(sub 1) states, which can interact with the paramagnetic O2 molecules, that are affected. However, our positron lifetime and Doppler broadening studies suggest the formation of (S(sub n).02) complexes which can also eventually reduce the population of the T(sub 1) states (i.e. quench phosphorescence). This is possible since higher triplet states in (Pt-OEP) are admixed with the S(sub n) states via spin orbit interactions. The experimental procedures and the results of various measurements are discussed in this paper.

Platinum Octaethyl Porphyrin (Pt.OEP) is an efficient phosphor under ultraviolet excitation. The phosphorescent triplet state (T(sub 1)) is readily quenched by the oxygen (O2) molecules. This phenomenon is being utilized as the basis for global air pressure measurements in aerodynamic facilities at various laboratories. The exact mechanism by which O2 molecules quench the (T(sub 1) - S(sub 0)) transitions is still unknown. The diamagnetic S(sub n) singlet states, which feed T(sub 1) states via intersystem crossings, would presumably not be affected by O2. It must be the magnetic T(sub 1) states, which can interact with the paramagnetic O2 molecules, that are affected. However, our positron lifetime and Doppler broadening studies suggest the formation of (S(sub n) central dot O2) complexes which can also eventually reduce the population of the T(sub 1) states (i.e. quench phosphorescence). This is possible since higher triplet states in (Pt.OEP) are admixed with the S(sub n) states via spin orbit interactions. The experimental procedures and the results of various measurements are discussed in this paper.

Correlation between Cu precipitates and irradiation defects in Fe-Cu model alloys investigated by Positron annihilation spectroscopy 作者： Shuoxue Jin 1 Peng Zhang 1 Eryang Lu 1 Liping Guo 2 Baoyi Wang 1 Xingzhong Cao 1  1 作者单位： 1. Institute of High Energy Physics, Chinese Academy of Sciences, 100049, Beijing, China 2. Key Laboratory of Artificial Micro- and Nano-structures of Ministry of Education and School of Physics and Technology, Wuhan University, Wuhan 430072, China 提交时间： 2017-03-26 摘要: 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 Fe-Cu model alloy Hydrogen ion-irradiation Cu precipitate defect Positron annihilation 分类： 物理学 &gt;&gt; 凝聚态:结构、力学和热性能 引用： ChinaXiv:201703.00573 (或此版本 ChinaXiv:201703.00573V1 ) doi:10.12074/201703.00573 CSTR:32003.36.ChinaXiv.201703.00573.V1 推荐引用方式： Shuoxue Jin,Peng Zhang,Eryang Lu,Liping Guo,Baoyi Wang,Xingzhong Cao,.(2017).Correlation between Cu precipitates and irradiation defects in Fe-Cu model alloys investigated by Positron annihilation spectroscopy.中国科学院科技论文预发布平台.[ChinaXiv:201703.00573] 版本历史 [V1] 2017-03-26 19:36:59 ChinaXiv:201703.00573V1 下载全文

Effect of annealing on Cu precipitates in H ion irradiated Fe–0.6%Cu studied by positron annihilation 作者： Shuoxue Jin 1 Peng Zhang 1 Eryang Lu 1 Baoyi Wang 1 Daqing Yuan 2 Long Wei 1 Xingzhong Cao 1 作者单位： 1. Multi-discipline Research Center, Institute of High Energy Physics, Chinese Academy of Sciences, 100049, Beijing, China 2. China Institute of Atomic Energy, Beijing 102413, China 提交时间： 2017-03-26 摘要: 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. Cu precipitate H ion irradiation Positron annihilation FeCu alloy 分类： 物理学 &gt;&gt; 凝聚态:结构、力学和热性能 引用： ChinaXiv:201703.00575 (或此版本 ChinaXiv:201703.00575V1 ) doi:10.12074/201703.00575 CSTR:32003.36.ChinaXiv.201703.00575.V1 推荐引用方式： Shuoxue Jin,Peng Zhang,Eryang Lu,Baoyi Wang,Daqing Yuan,Long Wei,Xingzhong Cao.(2017).Effect of annealing on Cu precipitates in H ion irradiated Fe–0.6%Cu studied by positron annihilation.中国科学院科技论文预发布平台.[ChinaXiv:201703.00575] 版本历史 [V1] 2017-03-26 19:36:59 ChinaXiv:201703.00575V1 下载全文

Detection of helium in irradiated Fe9Cr alloys by coincidence Doppler broadening of slow positron annihilation 作者： Xingzhong Cao 1 Te Zhu 1,2 Shuoxue Jin 1 Peng Kuang 1 Peng Zhang 1 Eryang Lu 1 Yihao Gong 1 Liping Guo 3 Baoyi Wang 1,2 作者单位： 1. Multi-discipline Research Center, Institute of High Energy Physics, CAS, Beijing 100049, China 2. School of Physical sciences, University of Chinese Academy of Sciences, Beijing 100039, China 3. School of Physics and Technology, Wuhan University, Wuhan 430072, China 提交时间： 2017-03-26 摘要: 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. Coincidence Doppler broadening spectroscopy Helium Micro-defects Alloys Ion-irradiation 分类： 物理学 &gt;&gt; 凝聚态:结构、力学和热性能 引用： ChinaXiv:201703.00583 (或此版本 ChinaXiv:201703.00583V1 ) doi:10.12074/201703.00583 CSTR:32003.36.ChinaXiv.201703.00583.V1 推荐引用方式： Xingzhong Cao,Te Zhu,Shuoxue Jin,Peng Kuang,Peng Zhang,Eryang Lu,Yihao Gong,Liping Guo,Baoyi Wang.(2017).Detection of helium in irradiated Fe9Cr alloys by coincidence Doppler broadening of slow positron annihilation.中国科学院科技论文预发布平台.[ChinaXiv:201703.00583] 版本历史 [V1] 2017-03-26 19:36:59 ChinaXiv:201703.00583V1 下载全文

Effects of thermal aging on Fe ion-irradiated Fe-0.6%Cu alloy investigated by positron annihilation 作者： HU Yuan-Chao 胡远超 CAO Xing-Zhong 曹兴忠 ZHANG Peng 张鹏 TSUCHIDA Hidetsugu 土田秀次 XU Qiu 徐虬 JIN Shuo-Xue 靳硕学 LU Er-Yang 卢二阳 LI Yu-Xiao 李玉晓 YU Run-Sheng 于润升 WANG Bao-Yi 王宝义 WEI Long 魏龙 作者单位： 1. Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049, China 2. College of Physical Engineering, Zhengzhou University, Zhengzhou 450001, China 3. Quantum Science and Engineering Center, Kyoto University, Uji 6110011, Japan 4. Research Reactor Institute, Kyoto University, Osaka 5900494, Japan 提交时间： 2017-03-26 摘要: 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 positron annihilation investigated 分类： 物理学 &gt;&gt; 凝聚态:结构、力学和热性能 引用： ChinaXiv:201703.00588 (或此版本 ChinaXiv:201703.00588V1 ) doi:10.12074/201703.00588 CSTR:32003.36.ChinaXiv.201703.00588.V1 推荐引用方式： 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.(2017).Effects of thermal aging on Fe ion-irradiated Fe-0.6%Cu alloy investigated by positron annihilation.中国科学院科技论文预发布平台.[ChinaXiv:201703.00588] 版本历史 [V1] 2017-03-26 19:36:59 ChinaXiv:201703.00588V1 下载全文

The nature of coordination defects in chalcogenide vitreous semiconductors of As-Ge-S system have been analyzed before and after gamma-irradiation using the results of positron lifetime measurements. The correlations between the positron lifetime data, the structural features and the chemical compositions of glasses have been established. The identification of negatively charged point defects has been carried out.

Recently, the gamma-ray telescopes AGILE and Fermi observed several middle-aged supernova remnants (SNRs) interacting with molecular clouds. A plausible emission mechanism of the gamma rays is the decay of neutral pions produced by cosmic ray (CR) nuclei (hadronic processes). However, observations do not rule out contributions from bremsstrahlung emission due to CR electrons. TeV gamma-ray telescopes also observed many SNRs and discovered many unidentified sources. It is still unclear whether the TeV gamma-ray emission is produced via leptonic processes or hadronic processes. In this Letter, we propose that annihilation emission of secondary positrons produced by CR nuclei is a diagnostic tool of the hadronic processes. We investigate MeV emissions from secondary positrons and electrons produced by CR protons in molecular clouds. The annihilation emission of the secondary positrons from SNRs can be robustly estimated from the observed gamma-ray flux. The expected flux of the annihilation line from SNRs observed by AGILE and Fermi is sufficient for the future Advanced Compton Telescope to detect. Moreover, synchrotron emission from secondary positrons and electrons and bremsstrahlung emission from CR protons can be also observed by the future X-ray telescope NuSTAR and ASTRO-H.

Positron - Electron Annihilation An analysis of the social, political and economic conditions which led to a split between the North and the South. The narration is supported with a music score of folksongs dramatizing the events as they are analyzed.

Thermoset polyimides have great potential for successfully meeting tough stress and temperature challenges in the advanced aircraft development program. However, studies of structure/property relationships in these materials have not been very successful so far. Positron annihilation spectroscopy has been used to investigate free volumes and associated parameters. It has been noted that the free volume correlates well with the molecular weight, cross-link density and thermal coefficient of expansion of these materials. Currently no other techniques are available for direct measurement of these parameters. Experimental results and their interpretations will be discussed.

The Oriented Scintillation Spectrometer Experiment (OSSE) on the Compton Gamma-Ray Observatory (GRO) has performed numerous observations of the galactic plane and galactic center region to measure the distribution of galactic 511 keV positron annihilation radiation and to search for time variability of the emission; the initial 511 keV line fluxes for the observations performed during the first 18 months of the GRO mission are presented. The 511 keV line flux for a typical galactic center observation is (2:5 plus or minus 0:3) x 10(exp -1) gamma sq cm s(exp -1), where the quoted uncertainty represents the 1 sigma statistical uncertainty. No statistically significant time variability of the line flux has been observed; the 3 sigma upper linit to daily variations from the mean is 3 x 10(exp -4) gamma sq cm s(exp -1). The distribution of galactic 511 keV positron annihilation radiation implied by the OSSE observations is discussed and compared with observations by other instruments.

A Positron Annihilation of Radiation Spectrometer (PsARS) was developed and characterized. PsARS spectroscopy as well as digital Positron Annihilation Lifetime Spectroscopy (PALS) was applied to measure positronium formation on gold manoparticles deposited through an evaporative method onto a thin capillary tube. This gold coated capillary tube was designed to be used for positronium lifetime studies in local electric field experiments. High local electric fields can polarize a positron-electron pair, which may result in an extended lifetime of the positron. These fields may be created through the interaction of an external electric field with silver manoparticles deposited onto the surface of gold coated capillary tubes. The capability to control size and distribution of silver manoparticles on such a surface is demonstrated. PsARS analysis of potassium dodecahydrododecaborate (dodecaborate) solutions was also performed to verify positronic dodecaborate species as well as potential positronium quenching.

A three-dimensional Positron Annihilation Spectroscopy System (3DPASS) capable to simultaneously measure three-dimensional electron-positron momentum densities measuring photons derived from annihilation events was designed and characterized. 3DPASS simultaneously collects a single data set of correlated energies and positions for two coincident annihilation photons using solid-state double-sided strip detectors (DSSD). Positions of photons were determined using an interpolation method which measures a figure-of-merit proportional to the areas of transient charges induced on both charge collection strips directly adjacent to the charge collection strips interacting with the annihilation photons. The subpixel resolution was measured for both double-sided strip detectors (DSSD) and quantified using a new method modeled after a Gaussian point-spread function with a circular aperture. Error associated with location interpolation within an intrinsic pixel in each of the DSSDs, the subpixel resolution, was on the order of 0.20 mm (this represents one-standard deviation). The subpixel resolution achieved was less than one twenty-fifth of the 25-mm2 square area of an intrinsic pixel created by the intersection of the DSSDs' orthogonal charge collection strips. The 2D ACAR and CDBAR response for single-crystal copper and 6H silicon carbide (6H SiC) was compared with results in the literature. Two additional samples of 6H SiC were irradiated with 24 MeV O+ ions, one annealed and one un-annealed, and measured using 3DPASS. Three-dimensional momentum distributions with correlated energies and coincident annihilation photons' positions were presented for all three 6H SiC samples. 3DPASS was used for the first experimental PAS measurement of the structure of oxygen defects in bulk 6H SiC.

A three-dimensional Positron Annihilation Spectroscopy System (3DPASS) capable to simultaneously measure three-dimensional electron-positron momentum densities measuring photons derived from annihilation events was designed and characterized. 3DPASS simultaneously collects a single data set of correlated energies and positions for two coincident annihilation photons using solid-state double-sided strip detectors (DSSD). Positions of photons were determined using an interpolation method which measures a figure-of-merit proportional to the areas of transient charges induced on both charge collection strips directly adjacent to the charge collection strips interacting with the annihilation photons. The subpixel resolution was measured for both double-sided strip detectors (DSSD) and quantified using a new method modeled after a Gaussian point-spread function with a circular aperture. Error associated with location interpolation within an intrinsic pixel in each of the DSSDs, the subpixel resolution, was on the order of 0.20 mm (this represents one-standard deviation). The subpixel resolution achieved was less than one twenty-fifth of the 25-mm2 square area of an intrinsic pixel created by the intersection of the DSSDs' orthogonal charge collection strips. The 2D ACAR and CDBAR response for single-crystal copper and 6H silicon carbide (6H SiC) was compared with results in the literature. Two additional samples of 6H SiC were irradiated with 24 MeV O+ ions, one annealed and one un-annealed, and measured using 3DPASS. Three-dimensional momentum distributions with correlated energies and coincident annihilation photons' positions were presented for all three 6H SiC samples. 3DPASS was used for the first experimental PAS measurement of the structure of oxygen defects in bulk 6H SiC.

The center of our Galaxy is a known strong source of electron-positron 511- keV annihilation radiation. Thus far, however, there have been no reliable detections of annihilation radiation outside of the central radian of our Galaxy. One of the primary objectives of the INTEGRAL (INTErnational Gamma-RAy Astrophysics Laboratory) mission, launched in Oct. 2002, is the detailed study of this radiation. The Spectrometer on INTEGRAL (SPI) is a high resolution coded-aperture gamma-ray telescope with an unprecedented combination of sensitivity, angular resolution and energy resolution. We report results from the first 10 months of observation. During this period a significant fraction of the observing time was spent in or near the Galactic Plane. No positive annihilation flux was detected outside of the central region (|l| greater than 40 degrees) of our Galaxy. In this paper we describe the observations and data analysis methods and give limits on the 511-keV flux.

This report summarizes research on the determination of: (a) the dislocation densities of both edge and screw components using two positron annihilation techniques; and (b) the density of hydrogen traps by analysis of electrolytic permeation measurements. Dislocation densities of single crystal iron specimens deformed in three different manners were in good agreement with disclocation densities obtained by ETCH-PIT and TEM methods on the same specimens as well as being bracketed by three earlier TEM investigations. The positron lifetimes were 114 psec. in the trap-free bulk, 165 in an edge and 142 in a screw dislocation. The first two of these values are in good agreement with values obtained several previous authors using poorly characterized specimens. It had been assumed that positron trapping in a screw dislocation was very unlikely - so the value for the latter tyep of dislocation is an important result. The binding energies of a hydrogen atom to an edge was deduced to be 37.4 and to a screw is 25.6 KJ/mole. The density of hydrogen at different strains was in good agreement with the number of dislocation traps. The occupancy sites along the dislocation was approximately 20 percent.

Modified adiabatic scattering function applied to positron annihilation in helium

The gamma ray line at 0.51 MeV originates from the annihilation of positrons. When a fraction of the positrons annihilate from bound states of positronium, the 0.51-MeV line is accompanied by a continuum of 3-gamma annihilation radiation at energies up to 0.51 MeV. Accurate calculations of the rates of free annihilation and positronium formation in a solar flare plasma are presented and positronium formation by charge exchange is discussed. The observability of the 3-gamma annihilation is increased by the inherent delay in the production and slowing down time of the positrons. It was concluded that such radiation could be detected at times late in solar gamma ray events when the continuum and prompt line emissions have essentially disappeared.

OSSE has measured the galactic longitude distribution of both the 511 keV annihilation line radiation and the three-photon positronium continuum within 40 degrees of the center. They have similar shapes, with a composite longitude distribution well represented by an 11 degrees FWHM Gaussian central bulge together with a possible broad disk component comprising as much as 15% of the integral flux between 40 degrees and 320 degrees longitude. Contributions from one or more discrete source(s) at or near the center with total annihilation radiation (line plus continuum) intensities of up to 4 x 10(exp -4) photons cu cm sec(exp -1) (2 sigma upper limit) are compatible with the observed distribution. The best estimate of the positronium fraction is 0.97 plus or minus 0.03. No evidence for variation in the positronium fraction is observed.

Previous endeavors in positron annihilation spectroscopy (PAS) at AFIT have resulted in the design and characterization of a second-generation three-dimensional positron annihilation momentum spectroscopy system (3DPAMSS) which combines two-dimensional angular correlation of annihilation radiation (2D ACAR) and coincident Doppler broadening of annihilation radiation (CDBAR) in order to measure electron momentum distributions in samples and thus characterize material defects. The focus of this particular research is to nondestructively measure negative defects in the crystal lattice of copper-doped, silver-doped, and undoped lithium tetraborate by 3DPAMSS spectroscopy using a Na-22 source and two high-purity germanium (HPGe) position-resolvable strip detectors. Lithium tetraborate is a candidate material for novel neutron detectors and characterizing its crystal structure is necessary to fully understand its properties. Several angular deviation and differential energy features are noted, which are translated to potential electron momentum distribution features and crystal defect characteristics.

A study of Cu precipitates in Fe ions irradiated Fe-Cu alloys by positron annihilation techniques 作者： X. Z. Cao 1 P. Zhang 1 Q. Xu 2 G. D. Cheng 1 H. B. Wu 1 X. P. Jiang 1 R. S. Yu 1 L. Wei 1 B. Y. Wang 1 作者单位： 1. Key laboratory of Nuclear Analysis Techniques, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing, 100049, China 2. Research Reactor institute, Kyoto University, Osaka 5900494, Japan 提交时间： 2017-03-26 摘要: 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. positron annihilation irradiated 分类： 物理学 &gt;&gt; 凝聚态:结构、力学和热性能 引用： ChinaXiv:201703.00560 (或此版本 ChinaXiv:201703.00560V1 ) doi:10.12074/201703.00560 CSTR:32003.36.ChinaXiv.201703.00560.V1 推荐引用方式： X. Z. Cao,P. Zhang,Q. Xu,G. D. Cheng,H. B. Wu,X. P. Jiang,R. S. Yu,L. Wei,B. Y. Wang.(2017).A study of Cu precipitates in Fe ions irradiated Fe-Cu alloys by positron annihilation techniques.中国科学院科技论文预发布平台.[ChinaXiv:201703.00560] 版本历史 [V1] 2017-03-26 19:36:59 ChinaXiv:201703.00560V1 下载全文

The time-dependent decrease in ortho-positronium (o-Ps) intensity detected in polymers during long-term positron annihilation lifetime (PALS) experiments has been extensively studied and modeled. This decrease in temperature dependent, polymer specific, source strength dependent and is noted to saturate as a function of source exposure time. Larger decreases and smaller saturation values are exhibited at lower temperatures. Additionally, at sufficiently high temperatures, a negligible decrease is detected. The time dependent decrease is recoverable at elevated temperatures. In contrast, the o-Ps lifetime component remains constant and independent of exposure time. Increasing the exposed sample volume by continuously varying the source-sample orientation dramatically decreases the reduction of o-Ps intensity.

We consider positron propagation in the interstellar medium and show that the positrons from the beta-plus decay chains of the radioactive nuclei Ni-56, Ti-44, and Al-26, produced in Galactic supernovae, can fully account for all the features of the diffuse Galactic 511 keV annihilation radiation observed by INTEGRAL/SPI. We also predict additional measurable features that can further test the origin of positrons and provide new information on the nature of the interstellar medium.

$\gamma$-ray spectra for positron annihilation with the core and valence electrons of the noble gas atoms Ar, Kr and Xe is calculated within the framework of diagrammatic many-body theory. The effect of positron-atom and short-range positron-electron correlations on the annihilation process is examined in detail. Short-range correlations, which are described through non-local corrections to the vertex of the annihilation amplitude, are found to significantly enhance the spectra for annihilation on the core orbitals. For Ar, Kr and Xe, the core contributions to the annihilation rate are found to be 0.55\%, 1.5\% and 2.2\% respectively, their small values reflecting the difficulty for the positron to probe distances close to the nucleus. Importantly however, the core subshells have a broad momentum distribution and markedly contribute to the annihilation spectra at Doppler energy shifts $\gtrsim3$\,keV, and even dominate the spectra of Kr and Xe at shifts $\gtrsim5$\,keV. Their inclusion brings the theoretical spectra into excellent agreement with the experimental $\gamma$-spectra across the full range of Doppler energy shifts. Additionally, the theory enables the calculation of the `exact' vertex enhancement factors $\bar{\gamma}_{n\ell}$ for individual core and valence subshells $n\ell$. They are found to follow a simple and physically motivated scaling with the subshell ionization energy $I_{n\ell}$: $\bar{\gamma}_{n\ell}=1+\sqrt{A/I_{n\ell}}+(B/I_{n\ell})^{\beta}$, where $A$, $B$ and $\beta$ are positive constants. It is demonstrated that these factors can be incorporated in simple independent-particle-model calculations to successfully reconstruct the true many-body annihilation $\gamma$-spectra. This formula can be used to determine the enhancement factors for positron annihilation with core electrons of atoms across the periodic table and condensed matter systems.

Cu precipitates in hydrogen ion irradiated Fe-0.3%Cu alloy investigated by positron annihilation spectroscopy 作者： Shuoxue Jin 1 Xingzhong Cao 1 Peng Zhang 1 Eryang LU 1 Liping Guo 2 RuiSheng Yu 1 Baoyi Wang 1 作者单位： 1. Key Laboratory of Nuclear Radiation and Nuclear Energy Technology, Institute of High Energy Physics, Chinese Academy of Sciences, 100049, Beijing, China 2. Key Laboratory of Artificial Micro- and Nano-structures of Ministry of Education and School of Physics and Technology, Wuhan University, Wuhan 430072, China 提交时间： 2017-03-26 摘要: 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 . Positron annihilation FeCu alloy Ion irradiation Thermal aging 分类： 物理学 &gt;&gt; 凝聚态:结构、力学和热性能 引用： ChinaXiv:201703.00570 (或此版本 ChinaXiv:201703.00570V1 ) doi:10.12074/201703.00570 CSTR:32003.36.ChinaXiv.201703.00570.V1 推荐引用方式： Shuoxue Jin,Xingzhong Cao,Peng Zhang,Eryang LU,Liping Guo,RuiSheng Yu,Baoyi Wang.(2017).Cu precipitates in hydrogen ion irradiated Fe-0.3%Cu alloy investigated by positron annihilation spectroscopy.中国科学院科技论文预发布平台.[ChinaXiv:201703.00570] 版本历史 [V1] 2017-03-26 19:36:59 ChinaXiv:201703.00570V1 下载全文

Previous forays by AFIT into positron research have resulted in the development of a new positron annihilation spectroscopy (PAS) technique and the procurement of a low-energy positron beam system. The primary purpose of this research was to design and build a state-of-the-art PAS laboratory at AFIT capable to address a myriad of DoD solid-state and surface physics questions. The main objectives were to acquire and assemble utilities to operate a positron beam, assemble and con gure an ultra-high vacuum (UHV) system for samples, design and build an interface with a magnetic eld to propagate positrons onto samples, and create a new version of the three-dimensional positron annihilation spectroscopy system (3DPASS). The 3DPASS, which measures coincidence Doppler broadening of annihilation radiation (CDBAR) and two-dimensional angular correlation of annihilation radiation (2D-ACAR), was characterized using a Cu-22Na positron annihilation source made as part of this project. Integration of the 3DPASS with low-energy positron beam will allow for energy-dependent, nondestructive characterization of materials using PAS.