Large-Angle Scattering ofNa24Gamma-Radiation

Scattering of the 1.38-Mev and 2.76-Mev gamma-radiation of ${\mathrm{Na}}^{24}$ has been observed at a mean angle of 135°. Mg, Al, Pb, and Hg scatterers were used, and three definite components of scattered radiation were observed. The softest, of energy about 200 kev, is Compton-scattered radiation; the next hardest, of energy 500 kev, is the positron annihilation radiation. The third has an energy between 1.1 and 2.8 Mev. It is due, in part, to bremsstrahlung, but seems to be somewhat too hard to be wholly explained by this process. It is not sharply resonant nuclear scattering since it appears nearly equally in Mg and Al, while only Mg should be sharply resonant. From the lack of sharp resonance with the ${\mathrm{Mg}}^{24}$ level at either 1.38 Mev or 2.76 Mev, it is concluded that these levels must be less than 1/100 ev wide and that the corresponding transitions are of quadrupole or higher order.