Calculations of inelastic cross sections for rotational excitation

Cross sections for scattering of N₂ (j=0) molecules on He atoms are calculated for relative energies below the excitation threshold for the N₂ (j=2) rotational state. The close coupling method is used and the coupled differential equations are solved numerically. Very sharp resonances (corresponding to a lifetime of 10^?10 sec) caused by quasistable states of the N₂He system are found in the calculated cross section, when the closed channels corresponding to the N₂ (j=2) states were included in the coupled equations. The position of the resonances is compared with the calculated energy eigenvalues of the corresponding two body potential. Furthermore the equilibrium concentration of the N₂He quasistable and orbiting states is calculated at 80 °K andp _{N 2}=1 Atm. Both concentrations are found to be 1%.     

Antiprotonic helium and lithium with one or two electrons

High rotational states of¯p He and¯pLi atoms with one or two electrons are calculated in the Born-Oppenheimer approximation, with a precision which allows a systematic study of diabatic effects. The lifetimes of the relevant¯peα and¯pee Li states are in the μs range.     

Interaction potentials of Hg* + He at moderate interatomic separations and the radiative decay of the Hg(63 P 2) metastable state in collisions with He atoms

By using the modified method of the Fermi pseudopotential and the effective Hamiltonian method, a multiconfiguration calculation of the potential curves is performed for the Hg(6^{1, 3} P _J ) + He and Hg(7^{1, 3} S _J ) + He interactions in the region of interatomic separations R≥5a ₀. In this calculation, the interactions of different excited configurations and the spin-orbit coupling of singlet and triplet states were taken into account. The Hg⁺ + He ion-atom interaction potential was obtained by the nonempirical configuration interaction method MRD-CI with the use of the relativistic effective core potential (RECP) for the Hg atom. Based on the calculated potential curves and the transition dipole moments, the process of radiative decay of the Hg(6³ P ₂) metastable state in collisions with He atoms is considered and the temperature dependence of the rate constant is calculated.     

Proton spectroscopic factors of Sm isotopes in the pairing-plus-quadrupole model

Proton spectroscopic factors have been calculated for the single-proton states in Sm isotopes with N = 84–92 by using the deformed quasiparticle wave functions obtained in the pairing-plus- quadrupole model. Comparison is given with the experimental data from the pick-up reactions (d, ³He) and (t, ⁴He) to the product nuclei ^145–153Pm. Effects of deformation on the spectroscopic factors are studied.     

Variational Calculation of 4He Tetramer Ground and Excited States Using Realistic 4He–4He Potentials

We calculated binding energies and wave functions of the ⁴He tetramer ground and excited states employing various realistic ⁴He?⁴He potentials which includes the currently most accurate one with the adiabatic, relativistic, QED and residual retardation corrections. We used our Gaussian expansion method (GEM) for ab initio variational calculations of few-body systems. We found that precisely the same shape of the short-range correlation (r _ij < 4Å) in the dimer appear in the ground and excited states of trimer and tetramer. The four kinds of the binding energies of the trimer and tetramer ground and excited states, ${B_3^{(0)}, B_3^{(1)}, B_4^{(0)}}$ and ${B_4^{(1)}}$ , for the different potentials exhibit perfect linear correlations over the range of binding energies relevant for ⁴He atoms; namely, six types of the generalized atomic Tjon lines were observed.     

A PSDPF interaction to describe the 1 ?ω intruder states in sd shell nuclei

In the level schemes of sd shell nuclei, there is generally at relatively low excitation energies, coexistence of normal 0 ?ω positive parity states and of intruder 1 ?ω negative parity states. The aim of the present work is to describe these intruder states in the full p-sd-pf model space with a ⁴He core allowing one nucleon jump between the major shells. To construct our PSDPF interaction, we first modified the p-sd and sd-pf cross-monopole terms and then applied a fitting procedure to adjust all PSDPF parameters by comparing an extended set of experimental and calculated excitation energies. Results obtained with the new interaction have been finally compared with experimental data for nuclei throughout the sd shell.     

Generalization of the Independent Pair Model to degenerate nuclear states

The equations of the Independent Pair Model for finite nuclei are generalized to nuclear states non describable by a single shell model configuration. As an application of these generalized equations to excited states, the energy of the excitedT=0,J ^π=0⁺ -state of⁴He has been calculated by an approximate solution. Using a spin-averaged square well potential with hard core and Serber exchange character, with all parameters beeing determined from two-nucleon data, the calculation yields an excitation energy of 21.58 MeV compared to the experimental value of about 20.1 MeV.     

Path integral Monte Carlo calculations of4He and6Li

We have performed Monte Carlo calculations to estimate the exact energies of model problems for⁴He and theL=0,1, and 2 states of⁶Li. Using a Feynman path-integral expression for the imaginary-time evolution operator, we recast the ground state energy as a sum over histories, which are then sampled stochastically. Use of a trial wave function dramatically improves the efficiency of the Monte Carlo method. For a state-independent Malfliet-Tjon potential, together with the Coulomb interaction, we find a ground state energy of ?28.00+0.20 MeV for⁴He, and a degeneracy of theL=0,1, and 2 states in⁶Li at about ?59.65+-0.50 MeV. Density distributions for these nuclei are also calculated.     

Study of 31P with the 29Si(3He,p)31P reaction

The ²⁹Si(³He, p)³¹P reaction has been investigated at a bombarding energy of 15.0 MeV. Excitation energies and angular distributions were measured for 28 levels below 7.2 MeV in excitation. L-values were extracted from DWBA fits to the data. Angular distributions for the low-lying states were compared with DWBA curves calculated from Nilsson-model wave functions.     

Structure of light unstable nuclei in continuum energies

The Coulomb breakup reaction of ⁶He into a ⁴He+n+n 3-body system is analyzed by applying the complex scaling method (CSM). We can derive the contributions to El and E2 transitions, not only from resonances, but also 2- and 3-body continuum states, which show the characteristic structure of the many-body unbound states in ⁶He.     

Helium-cluster decay widths of molecular states in beryllium and carbon isotopes

⁴He (i.e., α particle) and ⁶He emissions from possible molecular states in beryllium and carbon isotopes have been investigated using a mean-field-type cluster potential. Calculations can reasonably describe the α-decay widths of studied states in beryllium and carbon isotopes, and also ²⁰Ne, compared with experiments. For the nucleus ¹⁰Be, we discussed α-decay widths with different shapes or different decay modes, in order to understand the very different decay widths of two excited states. The widths of ⁶He decays from ¹²Be and α decays from ^13,14C are predicted, which could be useful for future experiments.     

The effect of expansion of the shell model space on the structure of the mass-15 nuclei

The structure of the natural and unnatural parity states of the¹⁵N-¹⁵O mirror pair, as well as theT=3/2 analogue states of¹⁵C, is discussed in terms of shell model calculations with a modified surface delta two-body interaction. The inert core is recomposed from⁴He to¹²C and the configuration space is systematically expanded to allow for an increasing number of particle excitations from the 1p into the 2s-1d shell. The relative importance of the 2s 1/2, 1d 5/2 and 1d 3/2 orbitals are evaluated. Some electromagnetic properties of levels are also calculated.     

Fragmentation of the yrast band in186Os atI π =18+ and disappearance of the collective minimum

High-spin states in¹⁸⁶Os have been populated by the¹⁸⁶W(⁴He,4n)-reaction at 55MeV. The emittedγ-radiation was detected with the OSIRIS spectrometer. The yrast band, for which the nucleus has a prolate shape, was found to terminate atI ^π =18⁺. Theγ-ray intensity is then distributed between several irregular sequences. Different to other cases of band termination, the minimum in the total routhian surface corresponding to a collective shape is calculated to disappear in this spin region, although the available spin of the valence nucleons is far from being exhausted. A different structure, which is dominated by non-collective states becomes yrast.     

Investigation of low-energy scattering in the nnpp system on the basis of differential equations for Yakubovsky components in configuration space

The s-wave differential equations for the Yakubovsky components characterizing the nnpp system have been solved by the method of cluster reduction. Two-cluster scattering at energies below the three-particle threshold in the singlet and triplet spin states has been considered. The MT I–III potential model has been used to simulate nucleon-nucleon interaction, and the Coulomb interaction between the protons has been taken into account. The singlet and triplet scattering lengths have been calculated for proton interaction with the triton (³H) and for neutron interaction with the ³He nucleus, and the deuteron-deuteron scattering length has also been determined. The low-energy behavior of the phase shifts and inelasticity factors in the corresponding scattering channels has been investigated. The features of the 0⁺ resonance in the ⁴He nucleus have been determined.     

Isospin mixing in the electric-dipole He(γ, n) and He(γ, p) reactions

Possible isospin mixing of the J^π = 1⁻ excited states of ⁴He leading to sizable differences in the ⁴He(γ, n)³He and⁴He(γ, p)³H cross sections in the giant-resonance region is examined in a bound-state approximation. Results indicate that the general features of certain experimental data can be accounted for by the presence of Coulomb mixing of the (S = 1, T = 0) and (S = 1, T = 1) states in addition to the usual spin-orbit mixing of the (S = 0, T = 1) and (S = 1, T = 1) states.     

A uniform quasi-classical description of radiative transitions for asymmetric rare-gas atom-atom collisions

The uniform quasi-classical approximation [14] is used to describe the optical spectra formed during asymmetric collisions between atoms of rare gases in which one of the atoms is in a metastable state. We consider the reactions He(2¹S) + Ne → He(1¹S) + Ne + ?ω and Ar(³P₂) + He → Ar(¹S) + He + ?ω, in which the optical transition mechanisms are typical of most rare gases. Quasi-molecular terms of excited states and radiative widths calculated in a unified semiempirical approach are used. Spectral characteristics are calculated for thermal collision energies in the entire frequency range, including the center and both wings of the forbidden line. For the blue wing, our results are consistent with the widely used Condon approximation at collision energies E ≥200 cm^?1. At lower collision energies and in the region of the red wing and center of the forbidden line, the spectral distributions that cannot be described in the Condon approximation are reproduced in the uniform quasi-classical approximation. Comparison with quantum-mechanical calculations by the strong-coupling method confirms the high accuracy of the uniform quasi-classical approximation in the entire range of radiation frequencies.     

Correlation investigations of the low-energy 10He spectrum

The spectrum of low-lying states in the ¹⁰He nucleus is investigated for the two-neutron transfer reaction ³H(⁸He, p)¹⁰He. The secondary beam of ⁸He nuclei with the energy 21.5 MeV/nucleon and a cryogenic tritium target are used in the experiment. The ¹⁰He ground state is observed in the missing mass spectrum at the energy of 2.1 MeV (Γ ～ 2 MeV) above the decay threshold. Analysis of the angular correlations of the ¹⁰He decay products yields the spin and parity of two excited ¹⁰He states, J ^π = 1^? in the energy range from 4 to 6 MeV and J ^π = 2⁺ at energies above 6 MeV.     

Constrained variational calculations of closed shell nuclei with the reid potential

Lowest-order constrained variational calculations with harmonic oscillator wave functions are carried out for ⁴He, ¹⁶O, and ⁴⁰Ca nuclei with the Reid potential. The results obtained with this simple method are in very close agreement with those obtained by renormalized Brueckner-Hartree-Fock theory with orthogonalized plane wave intermediate states. The A-dependence of the difference between the experimental and calculated binding energies for A = 2, 3, 4, 16, 40 and ∞ can be explained by a three-body cluster term coming either from a wrong off-energy-shell behavior of the Reid potential or a three-body force. The calculated radii of ¹⁶O and ⁴⁰Ca are ≈ 10% too small, indicating that the Reid potential may not be very realistic.