The Doppler-shift attenuation method was used to obtain the following mean lifetimes (in psec) for the indicated nuclear levels: 10 C(3.36), r=0.155 ±0.025; 10 B(3.59), r=0.150±0.015; 10 Be(3.37), r=0.189 ±0.020; 10 B (2.15), r= 2.7_ 0 .4 +0 -8 . A limit of r <30 fsec is obtained for 10 B (1.74), which is a factor of 8 greater than, and therefore consistent with, the lifetime computed from the analog 0 decay of 10 C. Transition strengths obtained from the 10 B(2.15) and 10 B(3.59) lifetimes are in good agreement with the effectiveinteraction calculations of Cohen and Kurath, as modified by Warburton et at. The 10 C(3.36) and 10 Be(3.37) states decay by analog E2 transitions: 2 + , r=l-»0 + , T=1, with 7%=±l, whose strengths are well described by calculations of Kurath's for an effective charge €«= € p =0.5. An upper limit was obtained for the corresponding transition 5.17 ->1.74 in 10 B(r*=0) which is consistent (factor of 4 greater) with the analog strengths observed in the T e -ztl nuclei.

Levels in Si~were populated with the reaction Mg (e, n)Si 9 and subsequent y radiation from the various levels was detected with a 37-cm Ge(Li) y-ray spectrometer. Beginning with the 4.08-MeV level, y-ray angular distributions (0'~0 & & 90') were measured at incident bombarding energies near threshold (Q0 =0.033 MeV) for levels with excitation energies between 4.08 and 6.38 MeV. The target was a Mg metal foil, on the order of 0.5 mg/cm thickness.Branching ratios and excitation energies of the various levels were deduced from y-ray pulseheight distributions. y-ray angular correlations obtained at G. bombarding energies near threshold were treated as originating from residual nuclei having magnetic quantum numbers m~= 2 and 2. Analysis of these angular correlations in terms of level spin and y-ray multipole mixing was then undertaken. Mean lifetimes (or limits) for these levels were determined using a variant of the Doppler-shift-attenuation method, which involves measurements of the attenuation for two targets of different stopping power. Both Mg foils and Mg 6-Au alloy foils (10 at.% Mg and 90 at.% Au) were used. From these measurements, excitation energies (in keV), level spins, and lifetimes (in fsec) for these levels were deduced; these are, respectively, 4079These data may be combined with the results of other investigations to arrive at a fairly complete level scheme for Si29 in the energy interval 0&E"(Mev) & 6.38, including a description of the electromagnetic decay properties. These properties are compared with model predictions of the properties of Si29.

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Excitation energies and nuclear lifetimes of states in "Ar have been measured by employing the reaction ' Ar(t, p)"Ar at a triton bombarding energy of 2.8 MeV. Protons were detected by an annular silicon surface barrier counter at an average angle of 174', and coincident y rays were detected by a 2&em' Ge(Li) counter positioned at angles of 30 and 120 . The extraction of nuclear lifetimes by the Doppler-shift-attenuation technique was made possible by the use of a solid argon target operated at 15 K. Experimental results for excitation energies (keV) and lifetimes (psec) are: