M. J. A. de Voigt

Shell-model calculations on the nickel isotopes

Abstract Binding and excitation energies, electromagnetic transition rates and multipole moments have been calculated for 57–66 Ni from many-particle shell-model wave functions with neutrons in the 2 p 3 2 , 1 f 5 2 and 2 p 1 2 orbits outside the 56 Ni core. The efiective two-body matrix elements are obtained from the modified surface delta interaction. The average absolute deviation between the calculated and experimental binding and excitation energies is 0.11 MeV (with the exclusion of 66 Ni). Electric quadrupole transition rates and moments are calculated with an effective neutron charge e n = (1.70±0.08) e , obtained from a least-squares fit to experimental data. Magnetic dipole transition rates and moments follow from five fitted effective reduced singleparticle matrix elements. The average absolute deviations between theory and experiment for the strongest E2 transitions (1–15 W.u.) and for the strongest M1 transitions (0.01–0.14 W.u.) are 3.5 and 0.03 W.u., while the average measured strengths are 7.0 and 0.07 W.u., respectively.

Shell-model calculations for masses 27, 28 and 29: electromagnetic transition rates and multipole moments

Abstract Electromagnetic transition probabilities, multipole moments and log ƒt values have been calculated from many-particle shell-model wave functions in a truncated 1 d 5 2 2 s 1 2 1 d 3 2 config space, with a maximum of four holes in the 1 d 5 2 subshell. The electric quadrupole transition strengths and moments are reproduced very well in a least-squares fit to 74 experimental data with one parameter, for the isoscalar effective charge, yielding the values ep = 1.6 e and en = 0.6 e. The results for magnetic dipole transition strengths and moments follow from adjusting two effective reduced single-particle matrix elements in separate least-squares fits to 17 experimental data in A = 27 nuclei and 21 data in A = 29 nuclei. The average absolute deviations between theory and experiment for E2 and M1 transition strengths are 3.0 and 0.05 W.u., while the average measured strengths are 7.7 and 0.08 W.u., respectively. Transitions from excited states above Ex = 4.8 MeV in 27A1 and from some low-lying states in 27Al and 28Si are poorly reproduced by the present model. Calculated strengths of transitions from analogue states are given. Previous conclusions about the single-particle character of M1 transitions and the collective behaviour of E2 transitions are confirmed. The experimental data of seven A = 27–29 nuclei are well reproduced in one general treatment with an appreciably lower number of free parameters than are required to obtain comparable results in collective model calculations.

The reaction 23Na(α, γ)27Al: (I). Yield curve, excitation energies and branchings of 27Al levels

Resonance strengths and decay schemes have been determined for twenty 23Na(α,γ)27Al resonances in the range Eα = 2.0–3.3 MeV. Spectroscopy of bound states is possible, even at relatively weak resonances, through the use of Ge(Li)γ-ray detectors. The reaction preferentially populates high-spin states. Calibration with neutron capture γ-rays leads to precision values for the excitation energies. New levels are reported at Ex = 6512.0 ± 1.5, 7443.7 ± 1.5 and 7661 ± 2 keV. The reaction Q-value is 10087.7 ± 1.3 keV. In addition, a survey is given of the 23Na(σ, γ)27Al resonances in the range Eα = 3.3–4.4 MeV.

The reaction 23Na(α, γ)27Al: (II). Spins, parities and mean lives of 27Al levels

Abstract Angular distribution and Doppler-shift attenuation measurements in the reaction 23 Na(α,γ) 27 Al lead to the spin and parity assignments J π = 7 2 + to the 27 AlE x = 4.58 MeV level, J π = 9 2 + to the levels at E x = 5.43, 5.67 and 7.17 MeV, J π = 11 2 + to the 6.51 MeV level and J π = 9 2 ( + ) to the 7.81 MeV level. The E α = 2.69, 2.79 and 2.81 MeV resonance levels have J π = 11 2 ( + ), 9 2 and 11 2 + , respectively. Several quadrupole/dipole amplitude mixing ratios and γ-ray transition strengths are also reported. The combined evidence of the decay of the resonance levels and bound states leads to lower limits of 7 2 , 3 2 , 5 2 , 5 2 and 7 2 for the spins of the 5.50, 5.96, 6.95, 7.44 and 7.66 MeV levels, respectively, and to similar spin limitations for seventeen resonances. Mean lives of the 3.00, 4.51, 4.58, 5.43, 5.67, 5.96, 6.51, 7.66 and 7.81 MeV levels are τ m = 88 ± 10, 315 ± 40, 19 ± 6, 32 ± 6, 16 ± 4, 24 ± 18, 17 ± 6, 19 ± 6 and 26 ± 6 fs, respectively. Upper limits are given for the mean lives of fourteen other bound states. Eight of these follow from additional 26 Mg(p,γ) 27 Al Doppler-shift attenuation measurements.

Levels of 31P from α-particle capture in 27Al

Resonance energies, strengths and decay schemes have been determined for seventeen 27Al(α, γ)31P resonances in the range Eα = 2.3–3.3 MeV. New levels of 31P are reported at Ex = 6503±3, 6792±3, 7117.7±1.0, 7441.4±1.0 and 8345.5±1.5 keV. The reaction Q-value is found as 9665.1 ±1.3 keV. Doppler-shift attenuation measurements lead to the mean lives τm, = 130±50, 300±80, 90±20, 90±50, 35±18, 220±90, 120±50, 17±14 and 39±10 fs for the 31P levels at Ex = 3.30, 3.41, 4.63, 4.78, 6.45, 6.79, 6.83, 7.44 and 8.35 MeV, respectively, and to eight upper and one lower limits for the mean lives of other levels. These lifetimes and the combined evidence of the decay of the resonance levels and bound states limit the possible Jπ values for many levels of 31P.

A study of the two-particle states in 42Sc from the 41Ca(3He, d) reaction

Abstract Energy levels in 42Sc have been studied in the proton stripping reaction 41Ca(3He, d)42Sc at a bombarding energy of 20 MeV with an energy resolution of about 10 keV. A total of 90 levels were identified below 6 MeV excitation energy. Differential cross sections were measured as a function of reaction anngle, and l-values and spectroscopic strengths were deduced from a DWBA analysis. T = 1 states with f 7 2 2 and f 7 2 p 3 2 configurations were identified from a comparison of the spectroscopic results from the present 41Ca(3He, d) experiment and previous 41Ca(d, p) studies. The individual spectroscopic strengths for the two members of the 0.62 MeV 1+ + 7+ unresolved doublet were determined by a measurement of the deexcitation γ-rays in prompt coincidence with the relevant reaction deuteron group. he results are discussed in terms of sum rules, and effective two-body interaction matrix elements are derived. The spectroscopic strengths for the low-lying transitions agree with the predictions from the coexistence model.