The 26Al(n,p)26Mg reaction has been studied using neutron spectra which closely resembled Maxwell-Boltzmann (M.-B.) distributions with thermal energies of kT=40 x l0 6, 31 and 71keV and also for E,= 270-350 keV. These energies correspond to stellar temperatures T9=4.6 x 10 -7, 0.36, 0.82 and 3.1-4.1, where T 9 is in units of 109 K. The partial cross sections for the p0-(pl-)transition are found to equal 26+10(1,850 • 150), 13 • 6 (124 • 17), 16 + 13 (84 _ 14) and 21 • 8 (72 • 15) mb for the above neutron spectra, respectively. The astrophysical reaction rate is determined for the combined Poand p 1-transitions to be NA(av) =(0.324+O.026, 20.5+2.7, 22.6+_4.3 and 38.7• • 106 cm 3 mole-1 s-1. The results are compared with previous investigations and with statistical model calculations.

Using Doppler-fm tw-photon excitation from the ground state 4fi46s2 'So the even-parity J = 2 levels of the 4f1'6s7d and 4f1'6s8d configurations as well e w the 4f1'6p2, 4f136s26p and 4fI35d6s6p configurations between 44760.4 and 47341.8 cm-' in neutral ytterbium have been investigated with regard to the hyperfine structure of the excited states and the isotope shift of these transitions. The experimental results for the hyperfine splitting constants have been analysed regarding passible singlet-triplet and configuration mixing. The experimental values have been compared with theoretical results obtained in an ab initio calculation. A strong iduence for the second-order hyperfine interaction could be established in both the 4f1'6r7d 3D2 and the 4f1'6s1Os 'So states.

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