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51.
P. Pakhlov 《中国物理 C》2008,32(6)
We present a search for new charmonium like states in e~ e~- annihilation using the initial-state radiation and the process e~ e~-→J/ψD~(*)~(*).The analyses are based on a huge data sample recorded near theγ(4S)resonance with the Belle detector at the KEKB e~ e~- asymmetric-energy collider. 相似文献
52.
目前,正负电子湮灭过程的核子激发态N*产生的实验数据主要来自于粲偶素能区。粲偶素衰变到核子激发态过程类似于其类时电磁形状因子测量过程,正反粲夸克短程湮灭提供了近乎于点源的胶子强子化过程。与γN,eN,πN反应互补,这一新的N*产生源具有同位旋和低自旋筛选的优势。综述了正负电子湮灭过程的核子激发态N*产生的实验情况和相关的唯象进展,同时讨论未来发展的一些新方向,如正负电子湮灭过程的核子激发态N*产物的一些新来源等。Up to now, the N* production from e+e- annihilations has been studied only around charmonium region. Charmonium decays to N*s are analogous to (time-like) EM form factors in that the charm quark annihilation provides a nearly pointlike (ggg) current. Complementary to other sources, such as πN, eN and γN reactions, this new source for N* spectroscopy has a few advantages, such as an isospin filter and a low spin filter. The experimental results on N* from e+e- annihilations and their phenomenological implications are reviewed. Possible new sources on N* production from e+e- annihilations are discussed. 相似文献
53.
Well-annealed 316L stainless steel was first cold rolled to 10% and 20% reductions in thickness and then irradiated by 50 keV He+ to a dose of 1 × 1020 He+/m2 at room temperature. Thermal desorption spectroscopy was used to investigate the helium desorption behaviour at different helium trapping states. The results showed that high-density dislocations had stronger inhibitory effect for helium desorption at temperatures from 800 to 1200 K. Positron annihilation Doppler broadening spectroscopy measurements were used to investigate the distribution of helium irradiation-induced defects. The S–E and ΔS–E plots clearly demonstrated that the helium irradiation-induced defects were trapped and restricted in motion by dislocations. The interaction between dislocations and helium irradiation-induced defects in deformed 316L stainless steel was investigated. 相似文献
54.
Chang-Zheng Yuan 《Frontiers of Physics》2015,10(6):101401
With its unique data samples at energies of 3.8–4.6 GeV, the BESIII experiment made a significant contribution to the study of charmonium and charmonium-like states, i.e., the XYZ states.We review the results for observations of the Zc(3900) and Zc(4020) states, the X(3872) in e+e− annihilation, and charmonium ψ(13D2) state, as well as measurements of the cross-sections of ωχcJ and ηJ/ψ, and the search for e+e−→ γχcJ and γY (4140). We also present data from BESIII that may further strengthen the study of the XYZ and conventional charmonium states, and discuss perspectives on future experiments. 相似文献
55.
We derive the basic canonical brackets amongst the creation and annihilation operators for a two (1 + 1)- dimensional (2D) gauge field theoretic model of an interacting Hodge theory where a U(1) gauge field (Aμ) is coupled with the fermionic Dirac fields (ψ and ψ). In this derivation, we exploit the spin-statistics theorem, normal ordering and the strength of the underlying six infinitesimal continuous symmetries (and the concept of their generators) that are present in the theory. We do not use the definition of the canonical conjugate momenta (corresponding to the basic fields of the theory) anywhere in our whole discussion. Thus, we conjecture that our present approach provides an alternative to the canonical method of quantization for a class of gauge field theories that are physical examples of Hodge theory where the continuous symmetries (and corresponding generators) provide the physical realizations of the de Rham cohomological operators of differential geometry at the algebraic level. 相似文献
56.
用正电子湮没技术(PAS)结合示差扫描量热法(DSC)研究了聚烯烃聚氨酯的自由体积特征和微相分离结构的关系.结果表明,硬段含量增加,自由体积孔洞平均半径和自由体积分数减小;丁腈聚氨酯相分离程度小,相应自由体积孔洞平均半径和自由体积分数小,而丁羟聚氨酯的情况正好相反.石英弹簧法对苯和乙醇蒸气的溶解和扩散行为的研究表明,聚烯烃聚氨酯的自由体积孔洞平均半径和自由体积分数与苯和乙醇溶剂蒸气的无限稀释扩散系数呈正相关,但它们的无限稀释扩散系数和自由体积分数关系无法用Fujita的自由体积模型描述,可能归因于它们对聚烯烃聚氨酯复杂的溶胀行为. 相似文献
57.
质子辐照不锈钢中氢气泡产生和演化研究 总被引:1,自引:0,他引:1
采用质子辐照模拟方法和正电子湮没寿命测量方法研究了质子辐照在国产改进型316L不锈钢中产生的氢气泡及其随辐照质子注量的演化过程。5×10^12,5×10^13,5×10^14/cm^2质子辐照的实验结果表明,辐照在不锈钢中产生氢气泡的尺度随辐照质子注量增加而增大,在质子注量为5×10^14/cm^2时氢气泡尺寸达到0.62nm,气泡的浓度随质子注量增加而减小。The bubble production and evolution in the home-made modified 316L stainless steel have been investigated by the proton irradiation simulation technique and the positron annihilation lifetime measurement. The experimental results of 5 × 10^12, 5 × 10^13 and 5 × 10^14/cm^2 proton irradiations show that the produced bubble size increases, while the bubble concentration decreases, with the increasing of the irradiation proton flueence. At the proton irradiation fluence of 5 × 10^14/cm^2 the bubble size reaches 0.62 nm. 相似文献
58.
将黑色素纳米颗粒(melanin nanoparticle,MNP)经聚乙二醇(polyethylene glycol,PEG)修饰制备得到PEG-MNP,随后通过与放射性的68Ga3+离子螯合,高标记产率地制备得到68Ga-PEG-MNP,标记产物稳定性良好。进一步将68Ga-PEG-MNP通过雾化方式制备得到68Ga-PEG-MNP PM2.5(particulate matter 2.5,size<2.5 μm)模拟颗粒,其经雾化小鼠吸入体内后,通过正电子断层扫描(positron emission tomography,PET)成像对小鼠进行全身显影,结果可见雾化的68Ga-PEG-MNP PM2.5模拟颗粒可由气管向肺部双叶区域扩散,并滞留于肺。体内的PET成像结果与离体放射自显影结果高度一致。 相似文献
59.
研究堆慢正电子源是获得高强度慢正电子束流的有效方式,国际上己建成多座装置并获得广泛应用.与常规同位素慢正电子源相比,研究堆慢正电子源的物理过程复杂,影响末端束流强度的因素众多,对其进行深入研究与合理建模是未来在中国绵阳研究堆(CMRR)上构建慢正电子源的基础.本文厘清了研究堆慢正电子产生的关键过程与物理机理,建立了预测末端正电子束流强度的理论模型,找到了影响其末端强度的主要物理量:快正电子体产生率、慢化体有效表面积、慢化体扩散距离、慢正电子从表面被提取到靶环末端的效率、及束流系统提取效率.用多种实验结果对模型进行校验,包括多个同位素慢正电子源的效率测量值,以及PULSTAR研究堆慢正电子源测量结果,充分验证了模型正确性.根据模型对各物理量的影响因素进行了分析,找到了需着重关注的影响因素,对未来源/靶结构的设计给出建议. 相似文献
60.
Mutsumi Tashiro Pradeep K. Pujari Shu Seki Yoshihide Honda Shigehiro Nishijima Seiichi Tagawa 《Radiation Physics and Chemistry》2000,58(5-6):587-592
Temperature dependence of positron annihilation lifetime spectra of polysilanes such as, poly(methyl-n-propylsilane) (PMPrS) and poly(di-n-hexylsilane) (PDHS) has been investigated. The τ3 in PMPrS is seen to increase monotonically around the solid–liquid transition temperature. The transition temperature and free volume are observed to depend on the molecular weight and/or packing of the backbones. For PDHS, a sharp change in τ3 and I3 is seen at the solid–solid transition temperature. Free volume radius probability density functions, above and below the transition temperature, are presented in PMPrS and PDHS. Positron studies are complimented by conventional thermal analysis studies. 相似文献