Search Results (10 total)

The level structure of ^132,134Ba was investigated in (p,t) transfer reactions. High resolution spectra (7–8 keV full width at half maximum) with targets from a mass separator allow us to resolve levels up to 4.0 MeV. New 0⁺ states are identified. The monopole transfer strength shows distributions similar to those observed for ^194,196Pt. This is consistent with the O(6) limit of the interacting boson approximation (IBA-1) model, without ruling out other, more microscopically based interpretations for the low-lying structure of these nuclei. We also compare with the IBA-2 model and geometrical model calculations. © 1996 The American Physical Society.

We have made experimental measurements in ¹⁷⁰Tm of the following: secondary γ rays, conversion electrons, and γ-γ coincidences from thermal neutron capture in ¹⁶⁹Tm, primary γ rays from average resonance capture with 2-keV and 24-keV neutron beams, and proton spectra from the (d,p) reaction on ¹⁶⁹Tm. From these data and those of previous investigations, we have identified more than 130 excited levels in ¹⁷⁰Tm below 1550 keV. Of these, 62 (with connecting transitions) are placed in 18 rotational bands with assigned Nilsson configurations. These results are in good agreement with a semiempirical modeling of ¹⁷⁰Tm level structure. Values for seven Gallagher-Moszkowski splittings and four Newby shifts have been obtained. These matrix elements show remarkably good agreement with calculation. Among the observed K^π=1^- and 2^- rotational bands, configuration mixing appears to play a significant role. © 1996 The American Physical Society.

This paper is an extension of a previous study of the ²⁰⁶Pb nucleus in the framework of the homology concept. It is concerned with the multiplet of states homologous to the 1.484 MeV, 11/2^- level of ²⁰⁵Tl, due to ‖9/2^-⊗ 11) / 2 ^-〉 coupling. The results obtained and the new assignments attributed to ²⁰⁶Pb confirm the importance of the homology concept in the spectroscopy of high excitation energy levels.

The two-neutron transfer reaction ¹⁴⁷Sm(p,t)¹⁴⁵Sm was studied at E_p=26 MeV. Angular distributions were measured for θ_lab=5°–50°. The strength of the two neutron monopole pairing phonon⊗particle configuration (n_-=1,n₊=1)⊗ν2f_7/2 is identified in odd mass ¹⁴⁵Sm and is found to be quasi-uniformly spread in two narrow groups of as many as 8+5=13 states. This unexpected large fragmentation is compared with the one in the core nucleus ¹⁴⁴Sm and with that from its isotone ¹⁴³Nd where the monopole pairing vibration is less fragmented. The couplings with other excitation modes are extracted.

Two-nucleon spectroscopic amplitudes are investigated using cross-section measurements and tensor analyzing powers for the ⁵⁸Ni(d→,α)⁵⁶Co and ⁴⁸Ti(d→,α)⁴⁶Sc reactions. Angular distributions of cross sections, and analyzing powers A_y, A_xx, and A_yy, were measured in steps of 5° from 10° to 65° at a bombarding energy of 22 MeV. Data were analyzed using full finite-range DWBA calculations including a realistic α-particle wave function. The L-mixing ratios for several strong unnatural-parity transitions have been determined from comparison of calculations with analyzing power data. These ratios are compared to predictions of shell-model calculations to deduce predominant two-nucleon configurations.

Wave functions of the α particle corresponding to different S- and D-state deuteron-deuteron overlaps, 〈dd‖α〉, were investigated using exact finite-range distorted-wave Born-approximation (DWBA) analyses of (d→,α) reactions. Cross sections, vector, and tensor-analyzing powers were measured for (d→,α) reactions populating the lowest J^π=7⁺ state in ⁵⁶Co at bombarding energies E_d of 16 and 22 MeV, the lowest 7⁺ state in ⁴⁸Sc at E_d=16 MeV, and the lowest 7⁺ state in ⁴⁶Sc at E_d=22 MeV. We find that DWBA analyses of tensor-analyzing powers produce satisfactory agreement with the data and that A_xx is especially sensitive to the D-state component of α-particle wave functions generated by different realistic nucleon-nucleon interactions.

The reaction ¹⁴⁴Sm(p,p’) has been studied with an energy resolution of 4–5 keV using 22 MeV protons. Angular distributions for states up to 4 MeV excitation energies are compared with distorted-wave and coupled-channels calculations including one-step and two-step excitations to study direct and sequential strength distributions. The results are compared with calculations in the nuclear field theory approach where quasiparticle-random-phase-approximation-like states and their mixing with two-phonon (quadrupole and octupole) states is taken into account. Reasonable agreement is obtained for both the positive and the negative parity states.

The ²⁰⁹Bi(p→,α)²⁰⁶Pb reaction has been studied at an incident proton energy of 22 MeV using a polarized proton source and a quadrupole-dipole-dipole-dipole spectrometer. The differential cross sections and asymmetries for transitions to levels of ²⁰⁶Pb up to an excitation energy of 5.333 MeV have been measured. Evidence for the presence of multiplets of ²⁰⁶Pb states homologous to the parent ²⁰⁵Tl states is discussed. The differential cross sections and asymmetries for the transitions to these homologous states are interpreted in terms of the experimental differential cross sections and asymmetries of the parent states as well as by theoretical calculations using both conventional Woods-Saxon and double-folded α-particle potentials. The differential cross sections and asymmetries for the low-energy states of ²⁰⁶Pb which involve the pickup of the h_9/2 proton outside the closed shell are analyzed.

Components of α-particle wave functions corresponding to d-d configurations are used to predict analyzing powers in the (d,α) reaction. Tensor analyzing powers, especially A_xx, are shown to clearly distinguish between wave functions generated by different realistic nucleon-nucleon interactions. Data for the ⁵⁸Ni(d,α)⁵⁶Co reaction to the 7⁺ stretched-nucleon-orbital state at 2.283-MeV excitation in ⁵⁶Co, measured with 22-MeV deuterons, are compared to predictions from the Argonne and Urbana interactions. Similar comparisons are made to data for the lowest J ^π=7⁺ state in ⁴⁸Sc populated by the ⁵⁰Ti(d,α)⁴⁸Sc reaction at 16 MeV.

The (p→,α) reaction on ²⁰⁸Pb has been studied at an incident proton energy of 22 MeV using a polarized proton source and a spectrometer. The angular distributions and the asymmetries for transitions to levels of ²⁰⁵Tl up to an excitation energy of 3 MeV have been measured. The analysis of these data by means of the finite-range distorted-wave Born approximation theory using either conventional Woods-Saxon and double-folded α-particle potentials has allowed us to make several new attributions of spin and parity.