Anharmonicities of γ-vibrations in deformed nuclei

The anharmonicities of γ-vibrations are studied within the multiphonon method in different even-even deformed nuclei where the first K^π = 2⁺ vibrational state appears well below the energy gap: ¹³⁰Ce, ^162–164Dy, ^164–168Er, ¹⁸⁶Os. The anharmonicities previously obtained in ¹⁶⁸Er appear to be a general property of these nuclei.     

Effect of temperature on the band structure of MnxHg1−xSe

The band structure of the solid solutions Mn_xHg_1–xSe is constructed on the basis of the band parameters obtained from the electrophysical and optical investigations of these solid solutions. It is shown that the band structure of Mn_xHg_1–xSe and the dynamics of the bands as a function of the composition and temperature are analogous to those for Cd_xHg_1–xTe. It is shown that the variation of the nonparabolicity of the band spectrum of Mn_xHg_1–xSe as a function of the temperature greatly affects the temperature coefficient of the change of the width of the optical forbidden band (d_gop/dT).Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 40–44, April, 1991.     

Half-lives and fine structure for the α decay of deformed even-even nuclei

The α-decay properties of well-deformed even-even nuclei are systematically calculated within the multichannel cluster model (MCCM). Instead of working in the WKB framework, the quasibound solution to the coupled Schro¨dinger equation is presented with outgoing wave boundary conditions, and the coupling potential is taken into full account in terms of the general quantum theories. The calculated α-decay half-lives are found to agree well with the experimental data with a mean factor of less than 2. The fine...     

The Λ particle as a probe of deeply bound single particle states in heavy nuclei

Decay rates of excited states in heavy hypernuclei have been calculated using shell model wave functions. The nuclear Auger effect determines the widths of the states in most cases. The exception is the radiative decay for theΛ particle in the 1p and in exceptional cases also 1d shell. In general, the natural widths of the highly excited states below the threshold for theΛ emission are smaller than the spacing between theΛ shells. Spectroscopy ofΛ bound states in heavy hypernuclei thus seems to be feasible.     

Effect of random magnetic fields on the hyperfine structure of Mössbauer spectra in paramagnetic single crystals

Under certain conditions, the⁵⁷Fe Mössbauer spectra of Al(NO₃)₃·9H₂OFe³⁺ single crystals exhibit new lines [1,2] (so-called z-lines) at an unusually high velocity of about 10.5 mm/s. The dependence of the positions and intensities of these z-lines on the magnitude and direction of an external magnetic field has been investigated. The appearance of the z-lines is explained by small random magnetic fields arising from magnetic nuclei in the crystal.     

n - \bar n transitions in nuclei and mixing of nuclear states with A and A−22

A new lower limit on the period of oscillations, sec, which follows from the stability of Fe, is found. This limit is almost 10 times larger than previous estimations. Pis’ma Zh. éksp. Teor. Fiz. 64, No. 7, 456–461 (10 October 1996) This paper is an extended version of the talk presented at the Workshop on Baryon Instability Searches, Oak Ridge, March 1996. Published in English in the original Russian journal. Edited by Steve Torstveit.     

The contribution of the first forbidden transitions to the nuclear β~--decay half-life

β-decay half-life is a key quantity for nuclear structure and nucleosynthesis studies.There exist large uncertainties in the contributions of allowed and forbidden transitions to the total β-decay life,which limits the resolution of the predicted β-decay half-life.We systematically study the contribution of the first forbidden(FF) transitions to the β~--decay half-life,and quantify it with a formula based on simple physics considerations.We also propose a new formula for calculation of the β~--decay half-life that includes the FF contribution.It is shown that the inclusion of the contribution of FF transitions significantly improves the precision of calculations of the β~--decay half-life.By fitting of the RQRPA results for neutron-rich Z=47,57 isotopes and N=80,94 isotones,the formula for the contribution of the FF transitions gives similar results as the RQRPA calculations.However,because of limited experimental data for the branching ratios of unstable nuclei,the fit parameters are not fully constrained.Therefore,the proposed formula for the β~--decay half-life is more suitable for calculations of half-lives than of the FF contributions.The formula could be used to predict the β~--decay half-life in nuclear structure studies as well as nucleosynthesis calculations in stars.     

Can strong electric dipole transitions in deformed rare earth nuclei be explained by the macroscopic behavior of the octupole phonon?

StrongE1 transitions of greater than 10^–3 Weisskopf units occur in many octupole states in the deformed rare earth region. It is shown using the droplet model that the electric dipole moment resulting from the macroscopic behaviour of the octupole phonon cannot by itself account for the observedE1 strengths, and it is observed that this result is consistent with the proposal of Donner and Greiner and of Zilges von Brentano and Richter that admixtures of the giant dipole resonance into the low energy octupole states are responsible for the fastE1 transitions. It is also suggested that calculations similar to those performed by Egido and Robledo forN 92 nuclei may be able to reproduceE1 transitions inN=94–104 nuclei.Supported by the National Science Foundation and the State of Florida     

Role of the quasiparticle structure in α-decays of superheavy nuclei

The one-quasiparticle structures of nuclei in the α-decay chains of ²⁸⁷114 and ²⁹³116 are studied using a modified two-center shell model. Two-quasiparticle states are revealed in the α-decay chain of even-even nuclei ^286,288114. The calculated values for Q _α are compared to the available experimental data. The termination of the α-decay chains by spontaneous fission is analyzed.     

New transitions in the β-decay of 36Ca

The β-decay of the T _z = - 2 nucleus ³⁶Ca was studied at the LISE3 magnetic spectrometer at GANIL. Two new proton-emitting states have been detected and the other nine known βp and βγ transitions have been remeasured with improved resolution. A simulation with the GEANT code has been applied to this experimental setup. A comparison with shell model calculations is given. Received: 19 September 2000 / Accepted: 28 February 2001     

Description of the gamov-teller β+-decays and (n,p) transitions in spherical nuclei

The results of calculations of the total log (t)-quantities for decays of neutron-deficit nuclei and strength functions of (n, p) transitions are presented. It is shown that in spherical nuclei the ¦g _A/g _V¦1·0 conditions hold for the constants of a weak interaction.Dedicated to the memory of M. Gmitro.     

Phonon–particle coupling effects in the single-particle energies of semi-magic nuclei

A method is presented to evaluate the particle–phonon coupling (PC) corrections to the single-particle energies in semi-magic nuclei. In such nuclei, always there is a collective low-lying 2⁺ phonon, and a strong mixture of single-particle and particle–phonon states often occurs. As in magic nuclei the so-called g _L ² approximation, where g _L is the vertex of the L-phonon creation, can be used for finding the PC correction δΣ^PC(ε) to the initial mass operator Σ₀. In addition to the usual pole diagram, the phonon “tadpole” diagram is also taken into account. In semi-magic nuclei, the perturbation theory in δΣ^PC(ε) with respect to Σ₀ is often invalid for finding the PC-corrected single-particle energies. Instead, the Dyson equation with the mass operator Σ(ε) = Σ₀ + δΣ^PC(ε) is solved directly, without any use of the perturbation theory. Results for a chain of semi-magic Pb isotopes are presented.     

Collective-pair structure of Kπ = 0+,1+,2+ bands in deformed nuclei

In the framework of the microscopic IBM the fermion pair structure for several collective excitations has been investigated. In this study the deformed nucleus ¹⁵⁶Gd is treated as an example. The theoretical method used consists of a combination of a triaxial Hartree-Fock-Bogoliubov method and a Hill-Wheeler method. We discuss the effects of keeping the structure of the collective S-, D- and G-pairs fixed as well as varying these structures. The combination of fixed S-, D-, and G-pairs with only one other set of S'-, D'- and G'-pairs is also investigated.     

Odd-even nuclei in the A ≈ 100 nuclear region

Extensive calculations for the odd-neutron Ru-Pd isotopes and odd-proton Tc-Rh isotopes for both positive- and negative-parity states within the proton-neutron interacting boson-fermion model are presented. The results on energy levels, electromagnetic properties and spectroscopic strengths of one nucleon transfer reactions are compared with experiments. A general good agreement is obtained.     

Effect of Ni deficit on the electronic structure and magnetic properties of PrNi2−xSb2

The influence of a Ni deficit in the nickel sublattice on the electronic and magnetic properties of PrNi_2−xSb₂ compound is investigated. The band structure is calculated using the LMTO method for x=0, 0.50, 1.0 and 1.5. At T=0 K the compound is antiferromagnetic with a magnetic moment on Pr close to 2.0 μ_B.