μ~-介子在He~3原子核上的俘获

本文计算了μ介子在He~3核上俘获的几率、末态H~3核的角分布和极化。所采用的理论是带有重正化效应(包含弱磁矩及赝标项)的V-A普适弱作用理论。在计算中考虑了μ和He~3核在始态有极化及处于不同超精细态上的情况。在计算中假定了He~3核的基态是纯S态,这时忽略了由张量力以及其他自旋轨道耦合力引起的其他态。介子交换电流的效应也没有考虑。在以上这两个假定下,我们证明了俘获几率中只包含一个未知的原子核矩阵元,这个矩阵元恰好是原子核密度函数的富氏分量。利用μ介子(或电子)与He~3(或H~3)原子核的散射可以确定这个未知矩阵元。     

μ-+Li6→He6+ν的俘获几率

本文计算了μ^-介子和原子核Li⁶在不同超精细结构状态上,μ^-+Li⁶→He⁶+ν的跃迁几率。指出在5％的误差范围以内,在两种超精细结构状态上俘获几率的比值和原子核矩阵元无关。     

μ-+He3→H3+ν过程的几率及原子核波函数

用三种不同的核波函数计算了u^-介子在He³核上的俘获几率,将结果与其他作者的结果进行了比较。     

μ-介子在Be7原子核上的俘获

利用考虑到重正化效果的普适V-A理论,本文计算了μ^-被Be⁷俘获后跃迁到Li⁷的基态与第一激发态的俘获几率,Li⁷核第一激发态的极化,以及由此跃迁到其基态时放出γ光的偏振度,其中对于不同的超精细结构态分别进行了计算,计算过程中,采用了壳层模型的原子核波函数。并假定忽略二次效应下,S态的四个核子没有参加作用。     

μ－在原子核上的俘获

利用多体场论方法,本文对μ^－在原子核上的俘获作了系统研究.在没有任何可调参数的情况下,对于从轻核到重核各种原子核上的μ^－俘获率作了计算.发现,自旋-同位旋相关的强作用的重整化效应及μ^－在原子核上的束缚能效应是透彻理解这种弱作用过程的关键.     

核子结构对质子俘获μ- 介子的影响

本文指出由于费曼—盖尔曼理论中弱相互作用与电磁相互作用的相似性,矢量耦合部分对质子俘获μ^-介子的贡献与核子的电磁形状因子相联系。本文给出了在重正化的V-A弱作用下质子俘获μ^-介子几率的公式,并根据电子核子散射的实验结果估计了核子的电荷、磁矩分布对μ^-介子俘获几率中矢量耦合部分贡献的修正。     

高能质子-核和核-核碰撞中末态作用对K+/π+比的影响

π介子与周围核子发生次级碰撞可以改变K⁺/π⁺比.本文用Glauber模型计算在质子-核和核-核碰撞中的K⁺/π⁺比.计算表明,末态相互作用对K⁺/π⁺比的效应是重要的.     

原子核中μ介子的辐射俘获

利用费密气体模型计算了原子核中μ介子的辐射俘获几率与所放出光子的极化,计算中包括了强相互作用的效应,利用规范不变性考虑了虚粒子放光子图形的贡献。     

相对论平均场理论研究原子核的磁矩

采用球形以及三轴形变的相对论平均场理论研究了满壳附近质量数A=133, 207, 209的原子核的磁矩, 分析了相对论效应以及核芯极化对磁矩的影响. 计算结果表明用包含矢量介子空间分量(奇时间分量)的三轴的相对论平均场理论 可以很好的描述满壳附近重质量区原子核¹³³Sb以及²⁰⁹Bi的磁矩.     

O3+与H2碰撞中非解离电荷转移过程的全量子计算

应用全量子的分子轨道强耦合方法，研究了基态的O³⁺(2s²2p ²P)与氢分子碰撞的非解离电荷转移过程，计算了不同方位角(25°，45°，89°)，能量分别为100，500，1000和5000eV/u时的单电子俘获的振动分辨的态选择截面及相应的微分截面.分子轨道强耦合计算中采用了自旋耦合价带理论计算的三原子分子势能面和径向耦合矩阵元.对氢分子的自身转动，采用无限阶的冲量近似方法；对体系的电子运动同H₂或H^+<     

The induced pseudoscalar interaction and the μ-capture in He3

Recent measurements ofμ-capture in He³ as well as the determination of the electric and magnetic formfactors of He³ and H³ allow a detailed analysis of theμ-capture process in He³. Assuming only the theory of a conserved vector current these experiments can be used to derive a relation for the axial vector part of the He³→H³ transition amplitude. This result is compared with a nuclear physics calculation of the formfactors. It follows that the induced pseudoscalar coupling constant for the muon capture on a free proton has a sign in agreement with the value predicted byGoldberger andTreiman. Its magnitude seems to be somewhat larger than the predicted value. We also find qualitative agreement with an extension ofNambu's idea of an almost conserved axial vector current to the case of the He³→H³ transition.     

Polarized electron capture by3He2+ at 20–28 keV

Nuclear polarization was measured by means of beam foil spectroscopy for a³He⁺ ion produced by an electron capture process of a³He²⁺ from a polarized sodium atom in an incident energy range from 20 to 28 keV. Assuming that a polarized electron of a sodium atom is predominantly captured to the 3d orbital of a³He⁺ ion andcascades down to the 1s ground state via the 2p orbital, an alignment factorA ₀ ^col (L=2) for the 3d orbital of a³He⁺ ion was extracted by comparing the observed initial sodium polarization andfinal nuclear polarization. The observedA ₀ ^col (L=2) showed a less pronounced energy dependence andwere qualitatively reproduced by the theoretical calculation.     

Properties of isovector 1+ states in A=28 nuclei and nuclear muon capture

A method is proposed for taking into account, in a calculation of partial rates of muon capture by nuclei, experimental information about strength functions for Gamow-Teller and isovector M1 transitions. The method, which amounts to choosing an orthogonal transformation that acts in the subspace of wave functions for excited states, requires neither modifying transition operators nor introducing effective charges. The matrix of the above transformation is constructed as a product of the matrices of reflection in a plane. All calculations are performed on the basis of the multiparticle shell model. Numerical results are obtained for isovector states in A=28 nuclei. Strength functions for Gamow-Teller and isovector M1 transitions in ²⁸Si are considered, and the lifetimes of 1⁺ states in ²⁸Al and the branching fractions for gamma decays of this state are calculated. Owing to taking into account experimental information about the properties of isovector states, the branching fractions for the γ decays of the 1⁺ state at 2.201 MeV in ²⁸Al are successfully described for the first time. The above transformation of the wave functions changes substantially the distribution of partial rates of allowed muon capture by a ²⁸Si nucleus among the 1⁺ states of the final nucleus ²⁸Al in relation to the results of the calculations with the eigenfunctions of the Hamiltonian of the multiparticle shell model. The muon-capture rates calculated with the transformed functions agree well with experimental data.     

Muon-capture rates and their relation with the double-beta decay

We discuss the non-radiative μ ⁻ capture (i.e. ordinary muon capture, OMC) in light nuclei in terms of the nuclear shell model, and in the medium-and heavy-mass nuclei in terms of the quasiparticle random-phase approximation. A new probe of the double-beta-decay matrix elements, namely the use of the OMC to states of the intermediate nucleus of the double beta decay, is also addressed. Presented by J. Suhonen at the Workshop on calculation of double-beta-decay matrix elements (MEDEX’05), Corfu, Greece, September 26–29, 2005.     

Electronic absorption spectrum of CO+ in an ion beam

The He+He⁺¹ interactions have been studied, as a function of the internuclear separation R, in terms of the electronic forces acting on the nuclei and the change in the charge distribution. The analysis reveals that at large R the atomic densities are polarized inwards, causing an attractive force on each nucleus, while at small R the difference in the nature of the interactions in the ²Σ_u and ²Σ_g systems is noted. It is seen that the He+He⁺¹ (²Σ_u) interaction is less attractive than the He⁺¹+He⁺¹ interaction at lower values of R.     

Photoproduction of hypernuclei and the algebra of currents

Using the apparatus of the algebra of currents, within the limits of soft kaons we calculate the differential cross section of the reaction He³ K⁺ AH³, in which the nucleus He³ and the hypernucleus AH³ are regarded as elementary particles. Under the hypothesis of particle conservation of axial current that changes the strangeness, this makes it possible to relate the amplitude of the process of photoproduction of a hypernucleus to the matrix element of a weak nuclear current between the states nucleus-hypernucleus and to express them in terms of the corresponding nuclear form factors. The coupling constant of the axial current,characterizing -decay of AH³, was assumed to be equal to –0.67, as in the case of a free A-particle.Translated from Izvestiya VUZ. Fizika, No. 12, pp. 53–55, December, 1971.The author thanks G. M. Radutskii and V. A. Filimonov for many fruitful discussions and for their attention to the work.     

Charge exchange in He++Li collisions

A two-state model, based on atomic wave functions and allowing for momentum transfer factors, is employed to calculate cross sections for the formation of excited states of He⁺ in collisions of He⁺⁺ ions with Li in the ground state, for energies in the range 5–64 keV. It is shown that the selective capture into the n=3 levels of He⁺, predicted at low energies by Shipsey et al., persists up to energies of ≈30 keV.     

Laser polarized muonic atoms

Lasers are an important tool in the field of muon physics. A new application of lasers, namely producing polarized muonic atoms, is the subject of a new program at LAMPF. One technique already demonstrated is stopping unpolarized muons in a laser polarized³He target. A more promising idea is to polarize neutral muonic helium by collisions with laser polrized Rb vapor. These methods for producing polarized muonic helium will be useful for measuring the spin dependence of nuclear muon capture and for determining the induced pseudoscalar coupling.     

Astrophysical S factors of radiative 3He4He, 3H4He, and 2H4He capture

The possibility of describing the astrophysical S factors for radiative ³He⁴He capture at energies of up to 15 keV and radiative ³H⁴He and ²H⁴He capture at energies of up 5 keV is considered on the basis of the potential cluster model involving forbidden states.     

Fission of muonic 232Th and 239Pu

The neutron emission is studied following the formation of muonic atoms of ²³²Th and ²³⁹Pu. Energy and time distributions are measured. Various processes which contribute to the measured spectra are considered. A collective resonance model of the muon capture is used to calculate the nuclear excitation function. The probability of the radiationless nuclear excitations and the influence of the presence of the bound atomic muon on the fission barrier are discussed. The existing data for the $\text{Γ}{}_{\mathrm{n}}\text{Γ}{}_{\mathrm{f}}$, are analysed. As a result of the analysis the rates of the prompt and delayed fission events (due to the radiationless mu-atomic transitions and the nuclear muon capture, respectively) are deduced from the experimental data to be 0.006/muon and 0.045/muon for ²³²Th and 0.10/muon and 0.49/muon for ²³⁹Pu, respectively. The increase of the fission barrier for muonic atoms is confirmed. The experimental neutron rates can be consistently explained only if it is assumed that in both nucleides the K_α radiationless transitions do not induce fission. The increase of the fission barrier for ²³⁹Pu is hence deduced to be not less than 1.2 MeV. The fate of the atomic muon after the nuclear fission is briefly discussed. Its influence on the interpretation of the present results is found to be small.