Incoherent scattering of 59.54 keV γ-rays at small momentum transfers

Abstract

Whole atom differential incoherent scattering cross sections for 59.54 keV γ-rays were measured for a number of elements in the region 29⩽ Z⩽82 at scattering angles 90, 60, 45 and 30° employing a reflection geometry set up and a graded shielding arrangement. A 6 cm 3 HPGe detector was used to detect the scattered γ-rays. All the 49 cross sections reported in this paper constitute the first experimental measurement and serve to fill the existing gaps in the cross-section data. The comparison of the measured cross sections with Klein–Nishina theory shows electron binding effects becoming significantly large at small scattering angles and for high Z elements. Incoherent scattering functions S( x, Z), corresponding to momentum transfer values 3.395, 2.4, 1.84 and 1.242 Å −1 were extracted from the measured cross sections and were compared with the theoretical predictions. The non-relativistic Hartree–Fock theory is found to be comparatively better than the Thomas–Fermi model. At small momentum transfer values and for high Z elements experimental values deviate more from Hartree–Fock theory also suggesting the need for a more rigorous second-order S-matrix calculations.