Search Results (18 total)

The ¹⁰B(⁷Be,⁸B)⁹Be reaction has been studied with an 84 MeV ⁷Be radioactive beam. The measured cross section determines the asymptotic normalization coefficients for the virtual transitions ⁷Be+p↔ ⁸B. These coefficients specify the amplitude of the tail of the ⁸B wave function in the two-body channel ⁷Be+p, and may be used to calculate the S factor for the direct capture reaction ⁷Be(p,γ)⁸B at solar energies, S₁₇(0). We find that S₁₇(0)  =  17.8±2.8 eV b.

We consider the single particle level density g(ε) of a realistic finite depth potential well, concentrating on the continuum (ε>0) region. We carry out quantum-mechanical calculations of the partial level density g_l(ε), associated with a well-defined orbital angular momentum l<~40, using the phase-shift derivative method and the Green’s-function method and compare the results with those obtained using the Thomas-Fermi approximation. We also numerically calculate g(ε) as a l sum of g_l(ε) up to a certain value of l_max<~40 and determine the corresponding smooth level densities using the Strutinsky smoothing procedure. We demonstrate, in accordance with Levinson’s theorem, that the partial contribution g_l(ε) to the single particle level density from continuum states has positive and negative values. However, g(ε) is nonnegative. We also point out that this is not the case for an energy-dependent potential well.

The structure of the low-lying levels in the mirror nuclei ⁵⁷Ni and ⁵⁷Cu is described within the extended unified model. The problem of single-particle energies in ⁵⁶Ni is treated in detail. ‘‘Bare’’ single-particle energies are extracted from existing experimental data for the energy levels in ⁵⁷Ni and ⁵⁷Cu by carefully considering the influence of the coupling to excitations of the core. Important contributions arise, influencing especially the results on the spin-orbit splitting. The differences between the Coulomb energy shifts of various orbitals in ⁵⁶Ni are discussed and compared with those resulting from Hartree-Fock calculations carried out using a broad range of Skyrme interactions. The parameters of the Woods-Saxon potential reproducing these neutron ‘‘bare’’ single-particle energies and the charge root-mean-square radius of ⁵⁶Ni are extracted. It is demonstrated that the contributions associated with the Thomas-Ehrman effect and the electromagnetic spin-orbit interaction are important and large enough to account for the differences between the Coulomb energy shifts of the single-particle levels in ⁵⁶Ni. © 1996 The American Physical Society.

The level scheme of ⁵⁷Cu is investigated via the ¹H(⁵⁸Ni,⁵⁷Cu-γ)2n reaction by using the recoil mass spectrometer MARS at the Texas A&M Cyclotron Institute. Three low-lying excited states are observed in ⁵⁷Cu at 1028 ± 4, 1106 ± 4, and 2398 ± 10 keV. The results are compared with well known excited states of the mirror nucleus ⁵⁷Ni. The measured excited states of ⁵⁷Cu allow recalculation of the astrophysical reaction rate for the stellar radiative proton capture reaction ⁵⁶Ni(p,γ)⁵⁷Cu. © 1996 The American Physical Society.

Absolute branching ratios for the β decay of ⁵⁷Cu to excited states up to 3.3 MeV in ⁵⁷Ni have been determined, including the l-forbidden Gamow-Teller transition to the first excited state in ⁵⁷Ni. Four transitions to excited states at 0.768, 1.113, 2.443, and 3.007 MeV are observed in addition to the superallowed decay to the ground state of ⁵⁷Ni. The measured branching ratio to the ground state is 89.9 ± 0.8% and the branching ratios to the four excited states are 0.94 ± 0.09%, 8.6 ± 0.6%, 0.17 ± 0.03%, and 0.35 ± 0.04%, respectively. In addition we have measured the ⁵⁷Cu half-life and find it to be 196.3 ± 0.7 ms, which is in good agreement with the most recent measurement. B(GT) values have been extracted from the new results and are compared to shell model calculations. © 1996 The American Physical Society.

The result of the study of the high-spin states of the ¹⁰²Ru using the incomplete fusion reaction of ¹⁰⁰Mo(⁷Li,[p,d,t]xnγ) at 49 MeV is presented. The experimental data are the result of particle–γ-γ coincidence and in-plane out-of-plane anisotropy measurements. The ground state band is extended up to E_x=5.719 MeV (J^π=16⁺), and two other negative parity bands are also extended to higher spins up to E_x=4.707 (J^π=13^-) and E_x=4.615 MeV. Shape coexistence in ¹⁰²Ru at lower excitation energies was investigated using a two-band mixing model. The high-spin features of ¹⁰²Ru are compared with the prediction of the cranked Nilsson model.

The Kr isotopes with A=72 to 84 are investigated within the interacting boson model (IBM-2) using two different approaches. In the first investigation the single-particle energies of the neutron and proton bosons are assumed equal, ε=ε_ν=ε_π, whereas the second investigation is based on their being different (ε_ν≠ε_π). The results of these calculations are compared with the experimental data and previous theoretical investigations. We also attempt to determine the shape transition in these nuclei.

We have investigated the odd-A Tc isotopes in the mass 100 region using the neutron-proton interacting boson-fermion model. The calculation is based on the validity of the Z=38 subshell closure. The results for the energy spectra and electromagnetic transitions are compared with experimental data and with results from other calculations which considered Z=50 as a valid closed shell for Tc isotopes.

Energy spectra, B(E2) values, and ratios of the neutron-rich even-even Mo isotopes in the mass 100 region have been investigated in terms of the neutron-proton interacting boson model. Two different approaches were used. The first investigation is based on the validity of the Z=38 subshell closure considering ⁸⁸Sr as a doubly magic core. In the second calculation Z=50 and N=50 were considered as valid closed shells leading to ¹⁰⁰Sn as a core. The results from both calculations are compared with experimental data.

The structure of ¹⁰¹Tc has been studied using the ¹⁰⁰Mo(⁷Li,α2n) reaction at 49 MeV. Both particle-γ and particle–γ-γ coincidence experiments were performed. The intensities of γ rays both in and out of the reaction plane were measured to obtain information on the ΔI of the transitions. A new band based on the πg_9/2 configuration was identified for the first time. To investigate the shape coexistence or configuration dependent deformation in this nucleus, interacting-boson-fermion-model and cranked shell-model calculations have been performed. Cranked shell-model calculations were used to interpret the states at higher excitation energies.

Breakup of 63-MeV and 42-MeV ⁷Li near the α-t threshold is examined from the astrophysical point of view. A new approach is made to extract indirectly astrophysical S factors. The S factors are compared with those deduced from radiative-capture measurements. It is shown that the energy dependence favors the recent capture data of Schröder et al.

High-spin states in ¹⁰³Rh have been studied using the ¹⁰⁰Mo(⁷Li,4nγ) reaction at 45 MeV. The in-beam techniques employed included relative γ-ray excitation functions, γ-γ coincidences, and γ-ray angular distribution measurements. Low-lying collective bands built on the 1g_9/2 and 2p_1/2 quasiproton states show large signature splitting. At higher excitation energies (2.346 and 3.399 MeV), two strong ΔI=1 cascades are also observed with small signature splitting. These latter bands probably arise from three quasiparticle configurations. The one quasiparticle bands are interpreted within the framework of the axially symmetric rotor-plus-particle model with a variable moment of inertia, the generalized particle-asymmetric-rotor model, and the interacting boson-fermion model. High-spin features of ¹⁰³Rh are compared with the predictions of the cranked shell model. All of the models indicate that ¹⁰³Rh is a soft nucleus which exhibits shape coexistence.

An investigation of the β^- decay of 0.59 s ¹⁴⁵Cs into levels of ¹⁴⁵Ba was undertaken to search for evidence of intrinsic reflection asymmetry in light rare-earth nuclei. E_γ, I_γ, γ-γ coincidence, angular correlation coefficients, and internal conversion coefficients were measured. The level scheme for ¹⁴⁵Ba up to 1.3 MeV has been constructed. The proposed spin and parity assignments are based upon the measured transition multipolarities and the γ?(hyγ angular correlation coefficients. The levels at 112, 175, 277, and 416 keV may be members of a decoupled K=1/2^- band with a decoupling parameter of -2 and a rotational parameter of 20 keV. The octupole deformed rotational structure which is observed in the light odd-A actinides is not readily identified in ¹⁴⁵Ba.

In-beam γ-ray spectroscopy in concert with both massive transfer and fusion reactions has been used to study high-spin states in the relatively neutron-rich ¹⁰²Ru and adjacent mass 100 transitional nuclei. Backbending in ¹⁰²Ru is shown to result from the alignment of a pair of h_11/2 neutrons. Blocking arguments and cranked shell model calculations support this. Alignment of a pair of h_11/2 neutrons in the g_9/2 proton band of ¹⁰³Rh changes the signature splitting and B(M1)/B(E2) ratios.

The level structure of the N=60 isotone ⁹⁹Y has been studied via the decay of ⁹⁹Sr. γ singles and γ-γ coincidence measurements have resulted in 71 γ transitions placed in a decay scheme with 26 levels. γ-ray multiscaling measurements give a ⁹⁹Sr half-life of 270±10 ms. Five rotational bands, including the previously identified K=(5/2) ground-state band, have been identified in ⁹⁹Y. Nilsson orbitals, with bandhead energies in keV in parentheses, associated with these five bands are (5/2)[422] (0), (5/2)[303] (487), (3/2)[301] (536), (1/2) [431] (1011), and (3/2)[431] (1119). The rotational features are consistent with an axially symmetric deformation in the range 0.3 to 0.4. The characteristics of these bands and their associated γ-ray transitions are discussed.

Six rotational bands have been found in ₃₉⁹⁹Y₆₀, ₃₉¹⁰¹Y₆₂, ₃₈⁹⁹Sr₆₁, and ₄₀¹⁰¹Zr₆₁. All bands have small and very similar values of ℏ² / 2I that indicate deformations of ∼ 0.3-0.4 and imply that these nuclei are among the most deformed known, with I∼0.8I_rigid. Relative strengths of intraband γ transitions suggest Nilsson orbital assignments of π5 / 2 [422] for the Y ground bands.

Beta-ray end-point energies for Rb and La fission products were measured on an on-line mass separator using a hyperpure Ge β spectrometer. Coincidence measurements were used to establish feeding relationships and to verfy level schemes in daughter nuclides. Q_β values are reported for ^88,94,96,98Rb and ^146,148La. Our results are compared with those from other experiments and with predictions of mass formulae.

RADIOACTIVITY ^88,94,96,98Rb, ^146,148La [from ²³⁵U(n, f)]; measured E_β, E_γ, βγ, γγ coin; deduced Q_β mass excess. On-line mass separation, HpGe, Ge(Li) detectors.