Abstract. New assignments of quantum numbers have been obtained for more than 50 levels in 2ssi between 8953 and 15915 keV excitation energy. They are based on the measurement of 7-ray angular distributions or anisotropics on 29 resonances of the 27Al(p,7) reaction and on the 24Mg(c~,7) resonance at E~ = 3355keV. A total of 15 high-spin states with I = 5-7 has been obtained and the spectrum of T = 1 states has been identified up to 15 915 keV excitation energy and a maximum spin I=6.

Abstract. The systematics of 7-decay modes and radiative widths of highly excited states in 28Si has been extended by taking 7-ray spectra on 60 resonances of the 27Al(p, 7) reaction in the range 1097keV_< E,_< 4492keV (12643 keV _< Ex _< 15915 keV) and on the 24Mg(e,7) resonances at E~ = 3355, 3431, 4003 keV (Ex = 12860, 12925, 13415 keV). The y-decay modes of levels in the sub-resonance region (Ex = 10-12.5 MeV) were studied with both the 27Al(p, 7) reaction and the 27Al(d, nT) reaction at Ee = 4, 5, 6 MeV. Information on radiative widths of levels was obtained by measuring the resonance strengths S 7 = (2I + 1)FpF~fF for 52 resonances of the 27Al(p, 7) reaction with an emphasis on prospective T = 1 states.

New shell model calculations have predicted several high-spin (P = 5 + and 6 +) levels in 28Si near 10 MeV excitation energy which are missing from or ambiguous in existing experimental studies. Angular distributions, linear polarizations and Doppler-shifts of ),-rays have been measured for the 7-decay of the Ep = 1,911 and 2,073 KeV resonances of the 27Al(p, 7) reaction in an attempt to discover these missing states or confirm the discrepancies between experiment and theory. The excitation energies and spin-parities of the resonances were determined as 13,424.4 _+ 0.2 keV, P=5 § and 13,582.3_+0.5 keV, P=6 +. States populated in the 7-decay of these resonances were assigned spins and parities as follows: 11,777keV, F=5+; ll,331keV, P=6+; 10,417keV, P=5+; 9,417 keV, P=4 + and 8,945 keV, P=5 +. On the basis of 7-ray transition rates T=I is assigned to the 13,424 keV level and T=0 to the 10,417 and 11,777 keV levels. With the new data excellent agreement is achieved between the experimental spectrum of 28Si and the new shell model predictions. These data provide evidence for a K~=3 + rotational band comprised by the 6, 276, 6,889, 8,945 and 11,331 keV levels. This band emerges also from the shell model wave functions as do the/U=0 + bands based on the ground state and the 6,691 keV state.

Abstract. The 2*Si level scheme up to 14.5 MeV excitation energy is reevaluated using information from two preceding papers. It consists of approximately 250 levels which are almost completely characterized according to the quantum numbers 1, re, T of the levels. The properties of positive-parity states are compared to the predictions of shell model calculations within the complete s-d basis space using the unified s-d shell Hamiltonian. A spectrum of 48 experimental T = 1 states between 9.3 and 16 MeV is reproduced with a rms deviation of only 150 keV. A calculation of radiative widths and 7-decay modes which uses free-nucleon 9-factors yields excellent agreement with experiment and confirms that quenching of M1 transitions is only marginal in 2ssi. The detailed shell model analysis of the T = 0 spectrum is extended to the limiting energy where T = 1 wave function admixtures, not contained in the theory, become important experimentally. This happens at 6-8 MeV above the yrast state, depending on the spin value. Altogether it appears that a spectrum of 171 levels below 14.5 MeV, which have positive or unassigned parity, is almost completely accounted for by the model. Apparent intruder states from outside the s-d shell space are observed at Ex=lO945keV (U=4 +) and 12860 keV (U= 6 +) and are interpreted as members of a K S = 0 + rotational band.

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