High-Frequency Limit of 15.1-MeV Bremsstrahlung

The 15.1-MeV scattering resonance in carbon is used to study the yield of photons at the high-frequency limit of the bremsstrahlung spectrum. A survey of the yield at 0° was carried out for several elements. The 0° yield at the limit increases strongly with the atomic number in agreement with recent calculations. Measurements of the 15.1-MeV isochromats from a thin thorium ($Z=90\mathrm{}$) target for several angles are presented and compared with available calculations. A value of 1.61±0.16 mb is obtained for $\left(\frac{k}{Z^2}\right)\left(\frac{d\sigma }{\mathrm{dk}}\right)$, the cross section integrated over angle. This is in reasonable agreement with theoretical values of 1.96 mb based on the inverse photoeffect and 1.74 mb as obtained from a direct evaluation of the bremsstrahlung matrix element in the extreme relativistic limit.