The 7-decays of levels in 26Mg have been investigated up to 12.5 MeV excitation energy by proton-7-ray coincidence measurements in the Z3Na(0~,pT) reaction at 14.2 and 16 MeV bombarding energy. Lifetime-measurements, made with the Doppler-shift attenuation method, and proton-7-ray angular-correlation measurements were performed at E,= 14.2 MeV. Many high-spin states were observed, among them levels at 6,978989(6 +) and 12,479(8 +, 7-) keV excitation energy. The spectrum of positive-parity states and their electromagnetic properties are reproduced with good accuracy by shell-model calculations which employ a unified s-d shell Hamiltonian and the unrestricted configuration space of the 0ds/2-1s1/2-0d3/~ shell. Members of five inferred rotational bands, with K~= 0 +, 2 +, 3 +, 0 + and 3-have been observed up to at least I= 6. The K~= 2 + band shows strong anomalies of excitation energies and E2 transition rates near the I= 6 state. The static intrinsic quadrupole moments calculated from the shell model wave functions indicate transitions from prolate to oblate deformation within the K~= 2 + band and also the ground state band. The lowest lying U =4 +. state appears to be "spherical" and cannot be associated with a rotational band.

A search for high-spin states in 288i has been performed by n-7 coincidence measurements in the 25Mg(e, nT) reaction at E~= 14 and i5.5 MeV. Spin-parity assignments of the observed levels were obtained from n-7 angular correlation and lifetime measurements at E~= 14.5MeV. The ?,-decay of the 9,t64keV level was investigated separately with the 27Al(p,?,) reaction at the Ep=2,160 and 2,312keV resonances. Rotational bands with K~=3 -(comprising levels at E~=6,879, 8,413, 10,188 and 12,204keV), K ~ = 5-(comprising levels at E~ =9,702, 11,577 and 13,741 keV) and K ~ =0 + (comprising levels at E~=6,691, 7,381, 9,164 and ll,509keV) were observed. The finding of the latter band supports the idea of coexisting oblate and protate shapes in zsSi. A level at 14,643keV excitation energy has the properties of the I~=8 + member of the ground state band. There are additional positive-parity high-spin states which do not fit into rotational bands. All types of positive-parity states are well accounted for by shell model calculations.

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Gamma-decay modes and spin(-parity) assignments of levels in 25Mg have been systematically investigated up to 10 MeV excitation energy by particle-y-ray angularcorrelation measurements with the 24Mg(d, PY) reaction at 6.5 MeV bombarding energy and with the 22Ne(e, ny) reaction at 11.8, 12.5, 14.4 and 15.5 MeV bombarding energy. A level scheme has been established which is comprehensive up to 8.3 MeV excitation energy for I<9/2 and up to 10 MeV for 9/2

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