P. R. de Kock

Shell model calculations on natural parity states in 10≦ A≦14 nuclei

Shell model calculations of natural parity states in the 10≦A≦14 mass region have been performed by assuming an inert4He core with the residual interaction in the 1p shell only. The modified surface delta interaction (MSDI) has been used as an effective two-body interaction. The MSDI parameters as well as the single-particle binding energies have been deduced from a least-squares fit to experimentally known levels in, firstly, the seperate10B,11B-C,12C,13C-N and14N nuclei, and secondly, the whole mass region 10≦A≦14. Multipole moments for ground states and M1 and E2 radiative widths for excited states have been calculated with the resultant wave functions.

Resonance strengths, branching ratios and mean lifetimes of nuclear energy levels in23Na

The gamma decay of the22Ne(p, y)23Na resonances in the proton energy rangeEp=1.0→2.0 MeV has been investigated with a 20cm3 Ge(Li) detector. Implanted targets were used. The absolute strengths of the strongest resonances were determined and the branching ratios of twenty resonance levels and several bound states are reported. Mean lifetimes of the levels atEx=2.078 MeV (18.7±3.5 fs), 2.393 MeV (580−190+370 fs), 2.641 MeV (88−14+20 fs), 2.985 MeV (4.0−1.0+1.3 fs), 3.679 MeV (24−4+5 fs), 3.915 MeV (7.4−2.0+2.5 fs) and 4.775 MeV (<2.0 fs) were obtained from measurements of the gamma ray Doppler shifts.

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.

Lifetime measurements on 26Mg and 29Si by Doppler shift attenuation

Abstract The lifetimes of the lowest bound states of 26 Mg and 29 Si were determined by means of Doppler shift attenuation measurements. The results are τ m = 300 +100 −60 95±25, > 5000and 2100 +4000 −1000 fs for 26 Mg (1) through (4) and τ m = 560±130, 830±260 and 24±14 fs for 29 Si (1) through (3), respectively.

Resonant absorption of the γ-radiation from the22Ne(p, γ)23Na reaction and the effect of rutherford scattering in the target on the width of the absorption curves

Gamma rays of energy 9.404 and 9.700 MeV were obtained from the reaction22Ne(p, γ)23Na at proton energies of 640 and 950 keV respectively and were resonantly absorbed in sodium metal. Isotopically separated22Ne targets on nickel backings were used. The following level widths for23Na were obtained:The 9.404 MeV level: Γ=65 ±40eV Γγ=2.2±0.7eV.The 9.700 MeV level: Γ=9.5−1.0+4.5 eV Γγ=5.6−0.8+1.2 eV.The disagreement between the results for the 9.404 MeV level and the previously determined values can probably be ascribed to proton scattering in the window of the gas target used in the latter measurement.

The calculation of logft values and spectroscopic factors for nuclei in the mass range 10–15

Wave functions obtained in previous shell-model calculations [1, 2] for states of nuclei with massesA=10–15 are used to calculate logft values and spectroscopic factors. These wave functions, which were based on a modified surface delta two-body interaction, comprise the following active shell-model spaces: the 1p3/2 and 1p1/2 orbitals for mass 10–14 nuclei and restricted combinations of the 1p1/2, 2s1/2, 1d5/2 and 1d3/2 orbitals for mass 15 nuclei, leading to four different calculations in the latter case. The calculated results support evidence that the modified surface delta interaction is a valid approximation to the effective interaction in light nuclei.

The widths of the 9.991-MeV and 10.165-MeV levels in 27Al

Abstract Gamma radiation from the decay of two resonances in the reaction 26Mg(p, γ)27Al at Ep = 1.785 MeV and 1.965-MeV, have been resonantly absorbed in aluminium to excite the states at 9.991 MeV and 10.165 MeV, respectively. In addition the γ-decay of the resonances have been studied in detail and angular distribution and yield measurements of the ground-state radiation performed. The following results were obtained: 9.991-MeV Level 10.165-Mev Level J π 7 2 (−) 5 2 + Γ t 1.2 ± 0.3 eV 23 ± 3 eV Γ p 0.5 ± 0.2 eV 22 ± 3 eV Γ γ 0.7 ± 0.2 eV 1 ± 5 eV The spin of the 9.629-MeV state in 27Al, excited at Ep = 1.409 MeV, was also determined and found to be 1 2 .

Relativistic calculations of quasielastic proton-nucleus spin observables using a complete Lorentz invariant description of the NN scattering matrix

Effective-mass-type medium effects are investigated by calculating complete sets of spin observables for quasiefree proton-nucleus scattering. Results are presented for a 40Ca target between 500 and 200 MeV. The principle conclusion is that the use of the incomplete five-term parameterization of the NN scattering matrix (the SPVAT form or the IA1 representation) is to be avoided since it can severely overestimate the importance of effective-mass-type medium effects on quasiefree spin observables.

Non-Normal Parity States in Mass 10-15 Nuclei

The modified surface delta interaction (MSDI) is used as the effective two-nucleon residual interaction in extensive shell-model calculations forA=10–15 nuclei; a He-4 core andj-j coupled extra-core nucleon configurations of the formP3/2nP1/2m (1d5/2,2s1/2)1 are employed. Level energies and wave functions for low-lying non-normal parity states are first obtained from a simultaneous fit to experimental energies over the entire 10–15 mass range. The wave functions are next tested by comparing predicted nuclear properties with experimental data: single-nucleon spectroscopic factors, beta decay lifetimes,M1 andE2 radiative transition widths as well asE1 andM2 radiative widths are calculated. In general good agreement between experiment and theory is obtained.