The interacting boson model is examined from a microscopic viewpoint using the generalized seniority scheme. The present discussion focuses on regions of the periodic table in which the many nondegenerate nucleon orbits can be approximated in terms of two nondegenerate orbits, the sum of whose occupancies is chosen to be the same as the total occupancy of the major shell being studied. Predictions for the interacting boson model parameters are obtained by constructing the zeroth-order boson images of the corresponding fermion operators. Calculations are carried out for the tungsten isotopes, and the predicted interacting boson model parameters are found to be in good overall agreement with the empirically determined values for the tungsten isotopes. The calculations reproduce the observed SU(3) or rotational character of the low-lying energy states in the N = 96 to 114 mass region.

NUCLEAR STRUCTURE Interacting boson model, microscopic determination of model parameters for two nondegenerate $j$ shells. Use of theoretical parameters to predict experimental results for tungsten.

Nuclear structure wave functions for the ground and excited states of light deformed nuclei are obtained by diagonalizing a "realistic" many nucleon Hamiltonian (kinetic energy plus a Brueckner $G$ matrix based on the Hamada-Johnston potential) in a suitably truncated nonorthogonal space of angular momentum projected deformed Slater determinants being constructed out of self-consistent Hartree-Fock single nucleon orbits. Possible spurious admixtures due to the center of mass motion are eliminated at least approximately by a separate diagonalization of the center of mass Hamiltonian. Taking into account a rather large single particle basis, calculations using this method are performed for the two $\mathrm{sd}$-shell nuclei ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$ and ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$. Besides energies and wave functions, using alternatively an oscillator and a Woods-Saxon representation, the electromagnetic ground state transitions of both parities and of various multipolarities are also calculated as well as the corresponding spectroscopic amplitudes. The results are compared, where possible, with the experimental data and the results of other calculations. Special attention is paid to the strength distributions obtained for the various multipolarities. Though completely microscopic, the model yields fair qualitative agreement with the available experimental information. Furthermore, possible improvements of the method are discussed.

NUCLEAR STRUCTURE ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$, ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$; calculated level schemes and electromagnetic transitions. Angular momentum projected Hartree-Fock and particle-hole method. Structure of the giant multipole resonances.

From the momentum space Faddeev equations we derive approximate expressions which describe the Coulomb-nuclear interference in the three-body elastic scattering, rearrangement, and breakup problems and apply the formalism to $p-d$ elastic scattering. The approximations treat the Coulomb interference as mainly a two-body effect, but we allow for the charge distribution of the deuteron in the $p-d$ calculations. Real and imaginary parts of the Coulomb correction to the elastic scattering phase shifts are described in terms of on-shell quantities only. In the case of pure Coulomb breakup we recover the distorted-wave Born approximation result. Comparing the derived approximation with the full Faddeev $p-d$ elastic scattering calculation, which includes the Coulomb force, we obtain good qualitative agreement in $S$ and $P$ waves, but disagreement in repulsive higher partial waves. The on-shell approximation investigated is found to be superior to other current approximations. The calculated differential cross sections at 10 MeV raise the question of whether there is a significant Coulomb-nuclear interference at backward angles.

NUCLEAR STRUCTURE Coulomb effects, approximation formulas; three-body elastic scattering, rearrangement, breakup; applied to $p-d$ scattering.

From an analysis of the experimental data, we assign $I^{\pi }=3^{-}$ (and $I=4^{+}$) levels in even ${}_{86}{}^{}{}_{}{}^{}\mathrm{Rn}$ nuclei. These levels, together with known levels with $I^{\pi }=1^{-}$ in ${}_{86}{}^{}{}_{}{}^{}\mathrm{Rn}$ and negative parity levels $K^{\pi }=0^{-}$; $I=1^{-},3^{-},\mathrm{and}{5}^{-}$ in ${}_{88}{}^{}{}_{}{}^{}\mathrm{Rn}$, ${}_{90}{}^{}{}_{}{}^{}\mathrm{Th}$, and ${}_{92}{}^{}{}_{}{}^{}\mathrm{U}$, demonstrate features of strong Coriolis coupling. The existence of strong Coriolis coupling effects is typical only for rotational bands based on one-phonon octupole vibrational states which include particles with large$j$ ($j_{\frac{15}{2}}$, $i_{\frac{13}{2}}$, etc.), but not for bands based on states $K^{\pi }=0^{-}$; $I=1^{-}$ with stable octupole deformation.

NUCLEAR STRUCTURE $A\gtrsim 218$ Rn, Ra, Th; analyzed levels, $\alpha$, $\beta$, $\gamma$ hindrances for octupole bands; deduced $I^{\pi }$ in ${}_{}{}^{218,220,222}{}_{}{}^{}\mathrm{Rn}$.

Excitation functions for inelastic scattering of ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ leading to the first $5^{-}$ state and ($2^{+}$ + $3^{-}$) states in ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ have been measured at the first maxima of the angular distributions. A monotonic increase with bombarding energy is observed for these cross sections, with no indication of the oscillatory structure seen for the 180° elastic scattering excitation function.

NUCLEAR REACTIONS ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$(${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$') inelastic scattering; $E_{\mathrm{lab}}=50-70\mathrm{}$ MeV, 0.5 MeV steps; coupled channel analysis.

We exploit a simple direct reaction model to explain the characteristic behavior of isotope production in heavy ion reactions. The temperature parameter can, in this way, be related to the mean energy loss per nucleon transfer and to the transfer probability. It is not connected with the thermodynamical temperature of a partially equilibrated nuclear system.

NUCLEAR REACTIONS Theory, statistical aspects of heavy-particle-induced transfer reactions.

Gadolinium isotopes were separated from a tantalum target which had been irradiated with 800-MeV protons. The concentrations of ${}_{}{}^{148}{}_{}{}^{}\mathrm{Gd}$ in weighed aliquots of a solution of the isotopes were determined by isotope dilution mass spectrometry. Other aliquots were counted on a low geometry alpha counter to determine the disintegration rate of ${}_{}{}^{148}{}_{}{}^{}\mathrm{Gd}$ per unit weight of solution. From the data obtained the half-life of the isotope was found to be 74.6±3.0 yr.

[RADIOACTIVITY ${}_{}{}^{148}{}_{}{}^{}\mathrm{Gd}$ measured $T_{\frac{1}{2}}$.]

It is shown that the formula for the breakup-fusion cross section, used successfully to explain observed massive transfer cross sections, having been derived originally by Kerman and McVoy, can be rederived, based on the optical theorem involving a complex potential.

NUCLEAR REACTIONS Breakup-fusion cross section.

The $B(E2,0^{+}\to 2^{+})$ value of the transition between the first excited $2^{+}$ state at $E_x=1.565\mathrm{}$ MeV and the ground state of ${}_{}{}^{86}{}_{}{}^{}\mathrm{Kr}$ has been measured by Coulomb excitation with ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ at bombarding energies ranging from 42 to 52 MeV. The result is $B\left(E2\mathrm{}\right)=0.128\mathrm{}\pm 0.10e^2{\mathrm{b}}^2$, if reorientation effects are neglected.

NUCLEAR REACTIONS ${}_{}{}^{86}{}_{}{}^{}\mathrm{Kr}$(${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$) ${}_{}{}^{86}{}_{}{}^{}\mathrm{K}$ŕ, $E=42-52\mathrm{}$ MeV, measured $\sigma (E,\theta )$, deduced $B\left(E2\mathrm{}\right)\mathrm{}$ value, Coulomb excitation.

It is shown that the energy dependence of the ratio of the strength of the Lorentz-scalar component to that of the Lorentz-vector component of the relativistic nucleon-nucleus potential as calculated from the $\sigma$,$\omega$ Hartree-Fock model is in fair agreement with the energy dependence found in phenomenological analyses.

NUCLEAR REACTIONS Energy dependence of scalar and vector components of relativistic optical model. Comparison between Hartree-Fock approximation and empirical evidence.

Distorted wave Born approximation calculations of differential cross sections for inelastic excitation of the giant dipole resonance with helium projectiles through the Coulomb field are presented. Competition with the nuclear excitation of the giant monopole resonance is discussed.

NUCLEAR REACTIONS ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$($\alpha$,${\alpha }^{\prime }$); $E_{\alpha }=96, 172.5, 480$ MeV; calculated $\sigma \left(\theta \right)$, giant resonances, Coulomb excitation.

It is shown that in the case of infinite nuclear matter the method recently introduced by Anastasio, Celenza, and Shakin for reducing the Dirac equation to a nonrelativistic Schrödinger equation yields the same Schrödinger-equivalent potential as a method used by previous authors.

NUCLEAR REACTIONS Equivalence in the limit of nuclear matter of two reductions of the Dirac equation to Schrödinger form.

The ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ ($\gamma$,$p_0$) reaction has been studied with linearly polarized bremsstrahlung photons in and below the giant $E1\mathrm{}$ resonance. The parity of the absorbed radiation was determined from the observed azimuthal asymmetry of the emitted protons. Combined with unpolarized measurements the polarized results determine the proton decay amplitudes of the $M1\mathrm{}$ resonance at $E_x=16.2\mathrm{}$ MeV in ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$. The shape of the unpolarized ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ ($\gamma$,$p_3$) angular distribution in the giant $E1\mathrm{}$ resonance was derived from the measured analyzing power.

NUCLEAR REACTIONS ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$($\gamma$,$p$), $E=15-25\mathrm{}$ MeV; measured analyzing power $\theta =90\mathrm{}°$ linearly polarized bremsstrahlung; ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ dipole levels deduced $\pi$; 16.2 MeV $1^{+}$ resonance deduced $p_0$ decay amplitudes; ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ GEDR deduced $p_3$ angular distribution.

In the past year several papers were published discussing, from very different points of view, the relation between the interacting boson approximation and the Bohr-Mottelson model. We show that, under certain assumptions about the measure in the Hilbert space, these approaches are equivalent.

NUCLEAR STRUCTURE Nuclear collective models, interacting boson approximation, Bohr-Mottelson model.

The newly observed $M1\mathrm{}$ states in the ($p$,$p^{\prime }$) experiment on the Zr isotopes are considered within the simple shell model. The calculation with a constant strength $\delta$ function interaction reproduces the excitation energies and the slight increase of the $M1\mathrm{}$ strength at small momentum transfer with mass number. We need about a factor of 2 quenching to reproduce the cross sections at small angles, which is in accordance with the general finding for magnetic transitions.

NUCLEAR STRUCTURE ${}_{}{}^{90-96}{}_{}{}^{}\mathrm{Zr}$; shell model calculations, $1^{+}$ states.

We have performed distorted-wave Born approximation calculations for the ${}_{}{}^{32}{}_{}{}^{}\mathrm{S}$($t$,$p$)${}_{}{}^{34}{}_{}{}^{}\mathrm{S}$ reaction, using two-neutron transfer amplitudes from a complete $2s-1d$-shell-model calculation. Results are in good agreement with previously published data for low-lying $0^{+}$ and $4^{+}$ levels, but fail to account for mixing of strengths among $2^{+}$ levels. Location of ${\mathrm{}\left(\mathrm{fp}\right)\mathrm{}}^2$ strength is confirmed.

NUCLEAR REACTIONS ${}_{}{}^{32}{}_{}{}^{}\mathrm{S}$($t$,$p$); calculated $\sigma (\theta ,E_p)$ with shell-model transfer amplitudes.

Level parameters in ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ have been determined by means of the resonance gamma-ray absorption technique and measurement of the azimuthal distribution of the elastic scattering of plane-polarized photons. The radiation was produced in suitably chosen ($p$,$\gamma$) reactions. The 7.1 MeV doublet was found at $E_x=7063.5\mathrm{}\pm 0.2 \mathrm{and} 7083.3\pm 0.3$ keV with ground-state radiation widths of 19.1 ± 1.5 and 9.1 ± 1.3 eV. A unique negative parity assignment could be made to both levels, in agreement with other observations. The 4.84 MeV bound level has an excitation energy $E_x=4842.2\mathrm{}\pm 0.2$ keV, and is most probably a $J^{\pi }=1^{+}$ level.

NUCLEAR REACTIONS ${}_{}{}^{34}{}_{}{}^{}\mathrm{S}$($p$,$\gamma$)Cl, ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ res. abs., ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ res. fluor., $E=4.8, 7.1$ MeV; measured $\sigma (E,E_{\gamma })$. ${}_{}{}^{208}{}_{}{}^{}\mathrm{Pb}$ deduced levels $\pi$, $\Gamma$, levels. Enriched lead sample.

Errors in earlier derivations of the density of unbound particle-hole states in the Griffin model are corrected. New expressions for the densities of states accessible in the two-body interactions are also derived. State densities calculated with the modified equations are compared with results of exact counting. Particle emission spectra calculated within the Griffin model are essentially unchanged, but the equal a priori probability assumption, found to be violated in the earlier work, is verified to a high degree of accuracy when the revised state densities are used.

NUCLEAR REACTIONS Rederived densities of unbound particlehole states and two-body interaction rates in Griffin preequilibrium statistical model. Verified equal a priori probability assumption.