Investigation of low-lying levels of the <Stack><Subscript>4</Subscript><Superscript>8</Superscript></Stack>Be nucleus in the multiquantum approximation of the orthogonal scheme

In the multiquantum approximation of the orthogonal scheme, specific calculations for the energies and radii of the ₄ ⁸ Be nucleus are performed with allowance for all states characterized by the λ=[44] Young diagram, the quantum numbers K_min and K_min+2 of the O(3(A?1)) group, and the quantum numbers E=K+2N (N≤9) of the U(3(A?1)) group. The convergence of the results with respect to the extension of the basis is studied, and the structure of relevant wave functions is revealed. The results of these calculations are compared with the results obtained in the analogous approximation of the unitary scheme.     

Microscopic Theory of Pinning of Multiquantum Vortex in Cylindrical Cavity

We have proposed and developed a microscopic model of depinning (escape) of a multiquantum vortex in a superconductor with a cylindrical nonconducting cavity with the transverse size smaller than or on the order of the superconducting coherence length ξ₀ at zero temperature. The spectrum of subgap quasiparticle excitations in two- and three-quantum vortices trapped by a cylindrical cavity has been calculated in the quasiclassical approximation. It is shown that the transformation of the spectrum is accompanied by break of anomalous spectral branches due to normal reflection of quasiparticles from the surface of a defect. A microscopic (spectral) criterion for multiquantum vortex pinning has been proposed; according to this criterion, the multiquantum vortex can be trapped in the cavity during the formation of a minigap in the elementary excitation spectrum near the Fermi level. Self-consistent calculations of density of states N(r, ε) for two- and three-quantum vortices trapped by a cylindrical cavity of radius on the order of ξ₀ have been performed using quasiclassical Eilenberger equations. In the pure limit and for low temperatures T ? T _c , peculiarities observed in the N(r, ε) distribution reflect the presence of M anomalous spectral branches in the M-quantum vortex and confirm the correctness of the spectral criterion of pinning (depinning) of a multiquantum vortex.     

Spectra and mean energies of prompt neutrons from <Superscript>238</Superscript>U fission induced by primary neutrons of energy in the region <Emphasis Type="Italic">E</Emphasis><Subscript><Emphasis Type="Italic">n</Emphasis></Subscript><20 MeV

The time-of-flight technique is used to measure the ratios R(E, E _n )=N(E, E _n )/N_Cf(E) of the normalized (to unity) spectra N(E, E _n ) of neutrons accompanying the neutron-induced fission of ²³⁸U at primary-neutron energies of E _n =6.0 and 7.0 MeV to the spectrum N_Cf(E) neutrons from the spontaneous fission of ²⁵²Cf. These experimental data and the results of their analysis are discussed together with data that were previously obtained for the neutron-induced fission of ²³⁸U at the primary energies of E _n =2.9, 5.0, 13.2, 14.7, 16.0, and 17.7 MeV.     

Study of Er171 decay by means of an electron-gamma coincidence technique

The decay scheme of Er¹⁷¹ (7.8 h) has been reinvestigated by means of an electron-gamma coincidence spectrometer and a scintillation spectrometer with a transistorized RIDL-400 channel analyser. A careful unfolding of the high energy region of the gamma-ray spectrum revealed the presence of photopeaks at energies of approximately 371, 404, 543, 572, 618, 675, 738, 796, 869, 910 and 962 keV. The existence of 32 transitions in Tm¹⁷¹ was confirmed. Also, it is proved that the 277, 362 keV transitions are in coincidence with the 210 keV and that the 175 keV transition is in coincidence with the 86 keV transition. We revealed the doubt for the existence of the 166, 210, 236, 277 and 419 keV transitions. From coincidence and single counting rates the followingK-conversion coefficients of the 111, 116, 124, 296 and 308 keV transitions were determined to be: α _K (111)=1.561±0.062, α _K (116)=0.699±0.035, α _K (124)=0.608±0.024, α _K (296)=0.0197±0.0010, α _K (308)=0.0183±0.0009, which give the 116, 124 keV transitions an electric quadrupole character; the 111 keV transition a magnetic dipole character withE2/M1 equal 0.4528; and the 296, 308 keV transitions an electric dipole character withM2/E1 equal 0.0058 and 0.0071 respectively.     

Soliton dynamics in a spin nematic

One-dimensional localized waves, which can be considered as soliton elementary excitations, exist in a magnet with a unit spin and comparable bilinear and biquadratic spin-spin interactions, with which the state of spin nematic is realized. These excitations are characterized by a certain momentum P and a certain energy E. The structure of these solitons has been found, and the E = E(P) dependence, which plays the role of the dispersion law of these soliton elementary excitations, has been constructed. The energy of a soliton with a certain momentum is shown to be lower than that of the quasiparticles of a linear theory. At small momenta, these E = E(P) dependences of the soliton and quasiparticles coincide asymptotically. The dependence of the soliton energy on the soliton momentum is a periodic function with a period P ₀ = π?/a, whose value does not depend on exchange integrals and depends only on a single crystal parameter, namely, the interatomic distance a. These soliton excitations have common features with the so-called Lieb states, which are well known in many condensed matter models.     

Treatment of pairing in small systems by Green functions

A finite system of fermions with pairing interaction is treated by the Green function method. It is shown that a finite number of “bound pairs” must be assumed to get the correct properties of the system in that region of the interaction strength where the BCS-solution is incorrect. Also the difference betweenE ₀(N+2)?E ₀(N) andE ₀(N)?E ₀(N?2),E ₀(N) being the ground state energy of theN-particle system, has to be considered. The formulae derived give an interpolation between the region where perturbation theory applies and the region of validity of the BCS-equations.     

Role of U(3(A−1)) multiquantum excited states in calculating spectroscopic quantities for 4 8 Be

A set of equations for deriving the SU(3)-irreducible density matrix for U(3(A?1)) multiquantum excited states involved is given. For the ₄ ⁸ Be nucleus, the binding energies, radii, spectra, electric quadrupole moments, and probabilities B(E2) of electric quadrupole transitions are computed in the multiquantum approximation of the unitary scheme. The values obtained for the above spectroscopic quantities are investigated versus the number of basis functions involved.     

Shape phase transitions in nuclei: Effective order parameters and trajectories

We analyze systematically the effective order parameters in nuclear shape phase transition both in experiments and in the interacting boson model. We find that energy ratios and B(E2) ratios can distinguish the first- from the second-order phase transition in theory above a certain boson number N (about 50), but in experiments, only those quantities, such as E(L ₁ ⁺)/E(0₂ ⁺) and B(E2; (L+2)₁ → L ₁)/B(E2; 2₁ → 0₁), etc., of which the monotonous transitional behavior in the second-order phase transition is broken in the first-order phase transition independent of N, are qualified as the effective order parameters. By implementing the originally proposed effective order parameters and the new ones, we find that the isotones with neutron number N _n = 62 are a trajectory of the secondorder phase transition. In addition, we predict that the transitional behavior of isomer shifts of Xe, Ba isotopes and N _n = 62 isotones is approximately monotonous due to the finiteness of nuclear system.     

Determination of absoluteK-internal conversion coefficients of some transitions in Ce140 by the internal-external conversion method

The internalK-conversion coefficients of the 331, 431, 815 and 933 keV transitions following the decay of La¹⁴⁰ have been determined absolutely by the method of comparing internal and external conversion lines measured in a double — focusing beta — ray spectrometers. TheK-internal conversion coefficients of the 4+→2+ 487 keV transition in Ce¹⁴⁰ was used to normalize relativeK-electron and gamma-ray intensities for these transitions. The results obtained are:α _K (331)=0.04432±0.00471,α _K (431)=0.28110±0.02913,α _K (815)=0.00396±0.00043,α _K (933)=0.00282±0.00031. Multipolarity assignments based on these values are suggested. The 815 keV transition is found to be pure magnetic dipole character in good agreement with the theoretical values calculated bySliv andBand. The 331 and 933 keV transitions are proved to have magnetic dipole character withE2/M1 equal 0.2852±0.0143 and 0.1750±0.0088 respectively. The 431 keV transition was found to have magnetic octupole character. The results obtained are most consistent with the assignment 2+, 4+, 2+, 3+ and 1+ for the 1597, 2084, 2184, 2410 and 2515 keV levels respectively.     

Study of penetration effects in the <Emphasis Type="Italic">E</Emphasis>1 and <Emphasis Type="Italic">M</Emphasis>1 transitions in <Superscript>44</Superscript>Sc

Conversion coefficients for the E1 and M1 transitions in the ⁴⁴Ti decay have been measured with high accuracy using the sum peak and multidimensional coincidence methods. The following values have been obtained: α_K(E1) = 0.077 ± 0.003 and α_K(M1) = 0.014 ± 0.001. A significant contribution of the penetration effects for the M1 transition has been shown. The penetration parameter λ is determined to be ?260 ± 30 has been determined.     

The shape of the giant dipole resonance for light nuclei

A complete spectrum of the giant dipole resonance is calculated taking into account the finite depth of the single particle potential. The mixing of the one particle-one hole excitations because of residual interactions is treated in the time-dependent Hartree-Fock approximation. If the interaction is approximated by a separable potential a general formula can be derived, which gives the total dipole excitation cross section σ(E) in terms of the simple shell-model cross section σ₀(E). Numerical results are given for O¹⁶ and C¹² by evaluating σ₀(E) in a square well potential.     

Study of photon electroproduction on the nucleon at high and low energy by Virtual Compton Scattering

Virtual Compton Scattering (VCS) and Deeply Virtual Compton Scattering (DVCS) on the nucleon are two processes accessed via the photon electroproduction reaction (eN → eγN). In the first part of this paper we are interested by the DVCS on the neutron. We measured the (D(e, eγ)X-H(e, e'γ)X) unpolarized cross section and we extracted, for the first time, a non-zero contribution of (neutron-DVCS + coherent- deuteron-DVCS) at Q ² = 1.75 GeV² and x _B = 36 from Jefferson Lab experiment E08-025. VCS on the proton has been studied at Mainz Microtron MAMI at the four-momentum transfer squared Q ² = 0.5 GeV², below the pion production threshold. In the second part of this paper we present our preliminary results of the structure functions (P _LL ? (P _TT/ε)) and P _LT, and the electric and magnetic generalized polarizabilities α _E (Q ²) and β _M (Q ²) extracted from this experiment.     

TheK-conversion coefficient of the 321 keVE1 transition in Hf177

TheK-conversion coefficient of the 321 keVE1 transition in Hf¹⁷⁷ has been measured by means of an iron free double focusing beta-ray spectrometer, using the internalexternal conversion method. The result obtained for α _K (321)=0.162±0.016 is in disagreement with the theoretical values for pureE1 transition (α _K =0.0154) calculated bySliv andBand. The large anomaly observed in theK-conversion process of the inhibitedE1 transition is compatible with a largeM2 admixture or, more probable with the presence of penetration matrix elements.     

Die absolute Intensität der durch Elektronenstoß in einer dicken Cu-Antikathode erzeugtenKα-Strahlung

The numberN _Kα ^dir (produced) ofKα-photons produced by electron-bombardment in a thick target of copper per incident electron has been measured absolutely with the Ross-filter method and relatively with the crystal-spectrometer method in the energy-region up to the four times theK-ionization energyE _K . The result can be presented in the following empirical form:N _Kα ^dir (produced) = 4π·

     

Electron and nuclear magnetic resonances associated with magnetoelectric and antiferroelectric interactions in the exchange-noncollinear (“square”) chiral antiferromagnet Nd<Subscript>2</Subscript>CuO<Subscript>4</Subscript> and their behavior in chiral phase transitions

Experiments with the tetragonal antiferromagnet Nd₂CuO₄ in the temperature range 1.5 K < T < T _N = 245 K show that the magnetic moments of Cu²⁺ possess an exchange-noncollinear magnetic structure of the “square” type, which has the form of an exchange doublet whose components exhibit different chiralities (Γ₄ and Γ₅ phases). Between these phases, consecutive phase transitions Γ₄ ? Γ₅ ? Γ₄ with a change in chirality take place at temperatures T₁ = 30 K and T₂ = 70 K. The electron and nuclear magnetic resonances (natural frequencies and susceptibilities) associated with excitation of magnons (due to the magnetoelectric and antiferroelectric interactions) by an ac electric field E(t), as well as a variable magnetic field H(t) applied in the case of a constant electric field E⁰, are calculated. It is predicted that nuclear magnetic resonance is excited by an ac electric field at frequencies determined by hyperfine fields of the sublattices. The change in the resonance frequencies upon the above chiral phase transitions are analyzed (being first-order phase transitions, these transitions possess a number of features associated with the chirality of the magnetic structures).     

The quadrupole moments of some even–even nuclei around the mass of <Emphasis Type="Italic">A</Emphasis> ~ 80: <Superscript>68−80</Superscript>Ge on the neighborhood of <Superscript>76−84</Superscript>Kr and <Superscript>76−84</Superscript>Se isotopes

We have carried out the calculation of the quadrupole moments Q(2₁⁺) and electromagnetic transition rates B(E2) of some levels within the framework of the interacting boson model for even-mass Ge nuclei. The presented predictions of the quadrupole moments and B(E2) ratios for Ge nuclei are compared with the results of some previous experimental and theoretical ones along with those of the neighboring Kr and Se isotopes and then it was seen that they agree well with the previous experimental and theoretical ones.     

Zero-sound branches in asymmetric nuclear matter

A polarization operator constructed in the random phase approximation is used to obtain zero-sound excitations in isospin asymmetric nuclear matter (ANM). Two families of the complex solutions ω_sτ(k),τ= p,n are presented. The imaginary part of the solutions corresponds to the damping of the collective mode due to its overlapping with the particle-hole modes and the subsequent emission of a proton (ω_sp(k)) or a neutron (ω_sn(k)). The dependence of the solutions on the asymmetry parameter is studied.     

Breit-Wigner parameters of the <Emphasis Type="Italic">S</Emphasis><Subscript>11</Subscript>(1535) nucleon resonance

The results of a partial-wave analysis of the angular distributions for the process γp → ηp over the energy range up to 2 GeV are presented. Reliable estimates of the Breit-Wigner parameters of the S₁₁(1535) resonance, as well as the energy dependence of the real and imaginary parts of the electric dipole amplitude E₀₊ and its phase, are derived from the energy dependence of the regression coefficient a₀(W).     

Effect of the Lattice and Spin-Phonon Contributions on the Temperature Behavior of the Ground State Splitting of Gd<Superscript>3+</Superscript> in SrMoO<Subscript>4</Subscript>

The temperature behavior of the EPR spectra of the Gd³⁺ impurity center in single crystals of SrMoO₄ in the temperature range T = 99–375 K is studied. The analysis of the temperature dependences of the spin Hamiltonian b ₂ ⁰ (T) = b₂(F) + b₂(L) and P ₂ ⁰ (T) = P₂(F) + P₂(L) (for Gd¹⁵⁷) describing the EPR spectrum and contributing to the Gd³⁺ ground state splitting ΔE is carried out. In terms of the Newman model, the values of b₂(L) and P₂(L) depending on the thermal expansion of the static lattice are estimated; the b₂(F) and P₂(F) spin-phonon contributions determined by the lattice ion oscillations are separated. The analysis of b ₂ ⁰ (T) and P ₂ ⁰ (T) is evidence of the positive contribution of the spin-phonon interaction; the model of the local oscillations of the impurity cluster with close frequencies ω describes well the temperature behavior of b₂(F) and P₂(F).     

Energy spectra of secondary particles in γ families and their sensitivity to the spectrum of primary cosmic rays

Spectra of secondary particles (γ-rays) in γ-families detected in the X-ray chambers in the Pamirs (H = 600 g cm^?2) have been analyzed. These γ-ray spectra show a bend at the energy E* _γ ≈ (ΣE _γ )^min, where (ΣE _γ )^min is the lowest total energy of γ-rays in the families above which γ-families were selected. The bend is not related to the knee in the spectrum of primary particles; it is due to the use of the ΣE _γ selection criterion. The E _γ spectrum slope is sensitive to the spectrum of the primary cosmic rays in the region E _γ ≥ (ΣE _γ )^min.