M1 radiation widths in Al27

Nuclear resonance fluorescence from energy levels in Al27 lying between 2 and 10 MeV excitation energy has been measured with bremsstrahlung beams of end-point energies of 7.66 and 10.37 MeV. Values of g0 and g0/ for 39 levels below 10 MeV were obtained from scattering cross section and self-absorption measurements. The measurements give an upper bound of total B(M1) below 7.7 MeV excitation which is about 25% less than the predictions of a large-scale shell model calculation based on the free-nucleon M1 operator. The same shell model wave functions combined with an effective M1 operator based on moments and transitions between low-lying states is in good agreement with the present experimental results.