Recent interests on positron (e⁺), positronium (Ps) and antihydrogen (<font style="text-decoration: overline;">H</font>)

A brief survey is made to highlight the recent interests in positron, positronium and antimatter physics. Positron is the first antiparticle observed which was predicted by Dirac. Positronium is itself its antiparticle and bi-positronium molecule is recently observed in laboratory which was predicted by Wheeler in 1946. The simplest antiatom i.e. antihydrogen is observed in the laboratory and the process to achieve the stable confinement of antihydrogen within the trap are in progress to test the standard model.

Plasma-screening effects on positronium formation

Plasma-screening effects on positronium （Ps） formation for positron-hydrogen collisions in a Debye plasma environ- ment is further investigated using the screening approximation model with the inclusion of the modified structure of Ps. More accurate Ps formation cross sections （n = 1,2） are obtained for various Debye lengths from the Ps formation thresh- olds to 50 eV. The influence of considering modified bound-state wave functions and eigenenergies for the Ps is found to result in the reduction of the Ps formation cross sections at low energies, whereas it cannot counteract the enhancement of the Ps formation by the Debye screening.

Positronium diffusion in porous methylsilsesquioxane thin films

Depth profiled positronium （Ps） annihilation lifetime spectroscopy （PALS） is an extremely useful probe of the pore characteristics in nanoporous low-dielectric （low-k） constant thin films. PALS has also been considered as a potential probe to investigate diffusion barrier integrity and the structural changes of porous low-k films during their integration with Cu. Hence, it is essential to understand the diffusion behaviour of positronium/Cu atoms in the films. In this work, based on the fact that porous materials possess characteristics of statistical self-similarity, a fractal model, the Menger sponge model, has been applied to simulate the structure of a promising dielectric, porous methylsilsesquioxane （MSQ） films. The diffusion behaviour of Ps out of the fractal model and into the surrounding vacuum is studied by means of the diffusion equation and traditional adveetive diffusive theory. Predictive results from our model show good agreement with measurement data.

Positronium formation for positron scattering from metastable hydrogen

Positronium （Ps） formation for positron impact on metastable hydrogen in 2s state has been studied by using the two- channel, two-center eikonal final state-continuum initial distorted wave （EFS-CDW） method. The differential, integrated, and total cross sections for Ps formation in different states have been calculated from each channel opening thresholds to high energy region. The results are compared with other theoretical calculations available in the literature. For Ps formation in s-state at intermediate and high energies, our results are in good agreement with the prediction of distorted wave theory. Those formed in p-states and the total Ps formation cross sections are reported for the first time. It is shown that the total Ps formation cross sections for positron scattering from H（2s） state are significantly larger at relatively low energies, while smaller at high energies, compared with those obtained from hydrogen in ground state.

Calculating the Relativistic Wave Functions of 11S0 and 13S1 Positronium

Based cn the relativistic Bethe-Salpeter (BS) equation, the positronium wavefunctions in Euclidean momentum space are obtained. Meanwhile the energy levels of positronium ground states 11S0 and 13S1 are fitted to be 6.7934 eV and 6.7929 eV respectively, which qualitatively agree with the previous theoretical values. It is shown that the BS theory is valid and reliable to treat positronium.

Positronium Formation in Positron-Lithium Scattering

The positronium formation process in positron scattering with atomic lithium is investigated using the coupled-channel optical method.The cross sections of positronium formation into the n=1 and n=2 levels from 2 to 60 eV are reported.The present results show reasonable agreement with the available experimental measurements and theoretical calculations.

Qualitative Analysis of Low-Lying Resonances of the Dipositronium Emerging from Ps-Ps and Ps-Ps* Collisions

An analysis of channel wave functions is made to clarify the types of resonance emerging from the Ps-Ps and Ps-Ps* collisions.The ordering of the energy levels of the states of the dipositronium is evaluated based on the inherent nodal structures of wave functions and on the existing theoretical results.The existence of a few very probable low-lying narrower resonances,namely the 0^(+)_(1)(A_(2)),1^(-)_(1)(E),…,benefiting from the centrifugal barrier has been suggested.

Existence of Two Higher L=0 Bound States of the Dipositroniums

Symmetry has imposed very strong constraints on the internal structure of quantum mechanical system.In particular,whether a state can access a given outgoing channel is constrained by symmetry.For the dipositroniums,the most important channel is the Ps-Ps channel.However,based on symmetry consideration it was found that only a few excited states are allowed to access the Ps-Ps channel,thereby at least the existence of two higher L=0 bound states(higher than the Ps-Ps threshold)has been affirmed.

Feature of a Confined Positronium Negative Ion by a Spherical Parabolic Potential

The ground and three low-excited states of the positronium negative ion Confined by a spherical harmonic oscillator potential are studied employing the adiabatic hyperspherical approach method. Total energies are obtained as a function of the confined potential radii. We find that the confinement may cause accidental degeneracies between levels with different low-excited states and the inversion of the energy wlues.

<i>L_α</i>Line of Dark Positronium as a Nongravitational Detection of DM

An attempt to predict the new atomic dark matter lines is done on the example of a dark lepton atom-positronium. Its Layman-alpha line with the energy near 3 GeV may be observable if the appropriate conditions are realized. For this we have studied a γ-ray excess in the center of our galaxy. In principle, this excess may be produced by the Lα line of a dark positronium in the medium with Compton scattering. The possibility of observations of an annihilation line (E^300 TeV) of dark positronium is also predicted. Other proposals to observe the atomic dark matter are shortly described. Besides, Hα line (1.3μ) of usual positronum must be observable in the direction on the center of our galaxy.

Discovered Solar Positronium

I describe a method for the observation of Positronium (Ps) involvement in the solar radiation spectrum. In this method, Rydberg-Ritz’s principle and Planck’s radiation formula are used to acquire information of the atomic transitions of Ps alike Hydrogen and Helium. In order to perform this experiment, an advanced solar spectrum monitor is constructed by utilizing light emitting diodes (LED) of various colors. A detailed study on this method provides qualitative agreement with experimental data, giving insight to the physical process involved in the solar radiation spectrum and confirming the existence of solar Ps.

Void Nucleation and Positronium Formation in Alumina Single Crystal

Void nucleation and positronium formation are studied by positron annihilationlifetime technique in α-Al2O3 irradiated by En≥1 MeV fast neutrons to a fluence of 3×1020 n/cm2.The voids of 0.7 nm are observed in the irradiated α-Al2O3 after the post-irradiationannealing at 850℃ and the positronium is formed in the voids.

变温下油脂自由体积和晶型结构演化的正电子湮没寿命研究

甘油三酯具有独特的同质多晶现象,其结晶和熔化特性对油脂产品性能及工业应用至关重要。利用正电子湮没寿命谱(PALS)可在原子尺度对结晶态甘油三酯的微观结构变化进行特征化描述。当正电子进入分子材料时,会与周围的电子形成电子偶素(电子-正电子的束缚态),其寿命反映了材料中空洞(自由体积)的大小。该文使用PALS首次研究了5种饱和脂肪酸甘油三酯的多晶性和晶型转变过程,包括甘油三月桂酸酯、甘油三肉豆蔻酸酯、三棕榈酸甘油酯、三硬脂酸甘油酯、花生酸甘油三酯。正电子数据和由其他表征手段得到的晶型变化规律很好符合。用正电子观察到更长分子链甘油三酯固相收缩成更稳定的晶型时有空洞形成,以及α晶在固-固转化过程中形成了2种β晶形态。

Physical design of positronium time of f light spectroscopy apparatus

Positronium time of flight spectroscopy（Ps-TOF）is an effective technique for porous material research.It has advantages over other techniques for analyzing the porosity and pore tortuosity of materials.This paper describes a design for Ps-TOF apparatus based on the Beijing intense slow positron beam,supplying a new material characterization technique.In order to improve the time resolution and increase the count rate of the apparatus,the detector system is optimized.For 3 eV o-Ps,the time broadening is 7.66 ns and the count rate is 3 cps after correction.

Positronium annihilation in silica aerogel studied by a positron age-momentum correlation technique

A high-performance positron age-momentum correlation （AMOC） spectrometer was newly developed. The counting rate is increased up to 200 cps much larger than the value 20 cps reported by other international groups. And at the same time, the time resolution still keeps at the international level of 220 ps. Furthermore, positronium （Ps） annihilation in silica aerogel was investigated by AMOC, which indicates： （1） Ps annihilation between the grains dominantly undergoes pick-off process and spin conversion from o-Ps to p-Ps; （2） Annealing below 400 ℃ changes the grain surface conditions, i. e. the desorption of hydrogen and the decrease of the defect centers concentration.

Positronium Annihilation in Oxygen and Nitrogen Mixture

Formed in silica aerogels, positronium annihilation in oxygen and nitrogen mixture is studied by a simple and convenient method. The results show that ortho-positronium （o-Ps） lifetime is significantly shortened when some oxygen is introduced into ni- trogen gas and that the o-Ps collisional quenching rate for an oxy- gen molecule is （28.0±0.4） ±ts%amagat（1 amagat 2.69± 1025 m-3）. It is found that the o-Ps annihilation rate in oxygen of latin at room temperature is （25.5±0.5） us-1 and that the effective num- ber of electrons per oxygen molecule available for 27 annihilation of positron in the o-Ps is （34.6±0.4）.

Chemical Quenching and Inhibition of Positronium in Cr_2O_3/Al_2O_3 Catalysts

The pore structure of Cr2O3/Al2O3 catalysts and the surface chemical properties of these pores were characterized by positron lifetime and coincidence Doppler broadening （CDB） measurements. Four lifetime components could be resolved from the positron lifetime spectrum, with two long lifetime components and two short lifetime components. The two long lifetimes τ4 and τ3 are attributed to ortho-positronium （o-Ps） annihilation in large pores and microvoids, respectively. With increasing Cr2O3 content, both τ4 and its intensity I4 show sharp decrease, while τ3 and its intensity I3 keep nearly unchanged. The Doppler broadening S parameters also show sharp decrease with increasing Cr2O3 content. Detailed analysis of the CDB spectrum reveals that the parapositronium （p-Ps） intensity also decreases with increasing Cr2O3 content. This indicates that the change of o-Ps lifetime τ4 is due to the chemical quenching by Cr2O3 but not spin-conversion of positronium. The decrease of o-Ps intensity I4 indicates that Cr2O3 also inhibits positronium formation.

Positronium Decay in a Circular Polarized Laser Field

We calculate the lifetime of both the o-Ps and the p-Ps positronium annihilation decay Ps →γγ in the strong circular polarized laser field. We take a strategy of the faztorization to separate the effects caused by the Coulomb interaction and the strong laser 6eld interaction. It is factorized in the time direction but not in the space direction. Our results show that in the laser with long wavelength and high intensity, the lifetimes of those Ps states are dramatically increased. For C02 laser with 10 μm wavelength and 1013 W/cm2 intensity, lifetime of the spin-single positronium is increased by 108 times. Our result is consistent with those obtained by solving the SchSdinger equation. This effect may be useful for the high harmonic generation （HHG） effects provided with the Ps [Phys. Rev. Lett. 70 （1993） 774; Phys. Rev. Lett. 93 （2004） 013601].

Photon Emissions from a Spinor Bose–Einstein Condensate of Positroniums

We investigate the quantum dynamics of the decay of a multiple-component positronium condensate into pairs of photons. A positronium atom has four internal spin states which are interconvertible through s-wave interactions. The quantum fields of all spin states of positroniums and photons are simulated from first principle in quasi-one-dimensional system using the truncated Wigner method. This method warrants us a full treatment of the depletion of positronium fields and the spin mixing induced by s-wave collisions between positronium atoms. Particularly,it yields the momentum spectrum of the emitted photons and the photon-photon correlations.

等离子体环境中正电子与氦原子碰撞电子偶素形成过程理论

正负电子偶素(Positronium,Ps)的形成是正电子-原子碰撞过程中独有的物理过程。为了探究正电子与氦原子散射过程中正负电子偶素形成的问题,应用屏蔽近似模型下的光学势理论方法研究了等离子体环境中正电子-氦原子碰撞的电子偶素形成过程,计算了0~100 eV入射能量区域内总的正负电子偶素形成截面(1s+2s)。在计算等离子体环境中靶原子体系的能级及波函数时,应用屏蔽的氦原子模型势描述了屏蔽效应对粒子间相互作用的影响。电子偶素形成截面计算结果与已有的其他理论、实验结果对比并进行了分析。验证了在中低入射能量下,屏蔽模型下的光学势理论方法对于处理正电子-氦原子散射问题具有有效性。