Vol. 21, No. 7 (1965)
Results of study on tubular Nb3Sn magnets are presented. Magnetic flux jumping has been observed as usual. The "frozen" field distribution is closely related to the external field distribution and previous history. The distribution need not be symmetrical with respect to the mid-plane perpendicular to the cylindrical axis, as in the case of soft superconductors. This confirms the suggestion that the sintered Nb3Sn material is not a homogeneous medium.We describe a new magnet structure with which magnetic flux jumping can be avoided. With these magnets, besides the use of the iron core for trapping magnetic flux, there are also special features in both the excitation and the measurement of magnetic fields.Utilizing the tubular Nb3Sn as a piston, we have obtained a highest magnetic field of 28.5kG at 1.5°K.
1965, 123 (7): 1355-1369. doi: 10.7498/aps.21.1355
The necessary conditions in the microscopic derivation of the Ginzburg-Landau (GL) equations are discussed, by showing that for a Pippard-or an intermediate-type superconductor the GL equations are valid only in a rather narrow region. Basing on the Gorkov equations for the thermodynamic Green functions of superconductor and using a nonlocal series of the "Green function of normal metal" in the magnetic field, we have derived a pair of coupled integro-differential equations for the energy-gap function and vector potential. These equations are valid for the Pippard- and intermediate-type superconductors in the same region near Tc as that for the London-type. The equations are applied to a semi-infinite superconductor in a static magnetic field. The integral expressions for energy-gap function and penetration depth are given. In the London and Pippard limit the integrals are performed analytically. For a superconductor of the Pippard-type, the corrections of energy-gap function and penetration depth due to magnetic field are calculated in the whole region near Tc. It is shown that the behaviour of a Pippard-type superconductor differs much from that predicted by the GL theory.
1965, 123 (7): 1370-1380. doi: 10.7498/aps.21.1370
The low energy opposite parity states of O17 and F17 are calculated by using the shell model method. The residual interaction between nucleons is considered as the δ-type force. First, the equations are solved under the L-S coupling approximation, and the result reveals that the low energy states possess the "pairing" coherent structure. Next, the spin-orbit coupling force is introduced by a certain approximate method, and an energy spectrum comparable with experiment is obtained. The transition probabilities corresponding to the existing experimental data are also calculated.
This paper studies with the help of perturbation theories the asymptotic properties of a ladder in the s channel as the momentum transfer t→∞ and some external masses M2→t1/2. The knowledge of such a property is essential to the calculation of the asymptotic property (as the momentum transfer t→∞) of a diagram which connects a ladder (in the s channel) and an ordinary pole in parallel.This paper studies also the absorptive part in the t channel of the above diagram, namely one which connects a ladder in the s channel and an ordinary pole in parallel. It proves that if the partial waves in the s channel possesses a Regge cut, the starting point of such a cut must lie to the left of the position given by current theories.
1965, 123 (7): 1387-1405. doi: 10.7498/aps.21.1387
Starting from π-N scattering amplitude and basing on the Mandelstam's representation and unitary condition, analyticity and threshold properties of fermion Regge trajectories of baryon quantum number 1 and strangeness 0 are investigated. The following preliminary results are obtained: (1) The position parameter of the Regge trajectories a(s) has a right-hand physical cut and no left-hand dynamical cut, but has a kinematical left-hand cut at s=0; (2) a(s) in the region s+(s) and α-(s), being of opposite space parity, are complex conjugate to each other. In the region 02, a±(s) are real but the dependence on s may be different; (3) The energy dependence of a(s) at the threshold is obtained; (4) Two kinds of Regge poles are distinguished. Those with a(W0)≠0 (W0-threshold energy) are responsible for dynamical resonances and bounded states. There are other kinds of the Regge trajectories for which a(W0)=0 and whose threshold behaviours are also investigated. As energy approaches the threshold from energy below the threshold, there are infinite pairs of poles approaching Re J=0 from the left half J-plane, each pair containing a couple of conjugate complex poles. While as energy approaches from above the threshold, there are also infinite pairs of poles approaching Re J=0, each pair containing poles in the first and third quadrant of the J-plane. For all these poles, Re α(s)→0 faster than Im a(s)→0 by one or two orders. The poles condense at the origin of the J-plane. We thus obtain the Gribov-Pomenranchuk condensation of the Regge poles in the case of Fermion trajectories. This kind of poles has a purely kinematical origin. They reflect the general properties of the S-matrix at the threshold.
1965, 123 (7): 1406-1418. doi: 10.7498/aps.21.1406
As a continuation of our previous work on the (stable) local modes and their effect on the absorption band width of isolated impurity centres, the problem of unstable local modes is considered in this article. By means of the method of group theory, both the unstable local modes and the scattered wave are classified according to the irreducible representations of relevant site group. The case of a simple cubic lattice with nearest neighbour interaction is discussed in detail and the related calculations are carried out. The results show that when a g-type unstable local mode has a rather narrow width, its contribution to the absorption band width may become so large that it exceeds the total contribution of all other lattice vibration waves. Finally, a brief discussion is given on the microscopic basis of the empirical formula of a "single effective frequency" of the electron-phonon coupling.
The method used in Ref.  to treat the magnetic susceptibility of the coupled system was extended to analyse the spin-lattice relaxation processes. In the case of weak coupling, the detailed expressions for the line shape of longitudinal nonresonance absorption and transverse resonance absorption were obtained by solving a set of coupled equations. The longitudinal and transverse relaxation times have been obtained as functions of the external alternating field. This is the direct consequence of the fact that the equations we used are of the non-Markovian type. Far away from the resonance point, the actual expression of the line shape is found to be quite different from that of the Debye or Lorentz type; the non-Markovian effect generally can not be ignored.In the case of S = 1, all the processes involved in the expressions of longitudinal and transverse relaxation times were systematically analysed. It is found that some terms correspond to the usually discussed processes such as one phonon process; the Orbach process, etc., but involve the frequency as a parameter as mentioned above. The influence of lifetime of phonons on the transverse spin-lattice relaxation was also discussed.
1965, 123 (7): 1456-1460. doi: 10.7498/aps.21.1456
A phase diagram of the alloys of the ternary system of silver-tin-aluminium wasconstructed on the basis of the data obtained by X-ray analysis. The phase diagram obtained consists of six single-phase regions (namely a, μ, β, γ,Sn, and δ regions), eight two-phase regions (namely α+μ,α+β,β+μ,β+γ,γ+Sn,β+Sn,β+δ and Sn+δ regions), and three three-phase regions (namely α+β+μ,β+γ+Sn and β+Sn+δ regions). No new phase was observed in these alloys of the ternary system.