Accurate determination of Compton backscattering in germanium at 86.5 keV on an absolute scale

The double-differential cross section d(2)sigma/d Omega dE for Compton backscattering in germanium was measured at the photon energy of 86.5 keV. The experimental setup with two high-purity germanium detectors operating in the coincidence mode was applied. A multiline radioactive sourer of Eu-155(63) was used as the source of photons. The Compton spectrum with a very small background was obtained. A fast cascade was found to little influence the data due to the 86.5 keV crossover transition. The contribution of a group of processes, which is described as double cross talk between the two detectors, was also studied and results of calculations show their weak intensity. The calculations of other processes were made as in our earlier papers. The values of d(2)sigma/d Omega dE were determined to an accuracy of better than 4% on an absolute scale in a broad energy region. The calculated values using the impulse approximation with hydrogenlike wave functions do nor, reproduce well the cross sections in some energy regions.