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

Whole atom differential incoherent scattering cross sections for 59.54 keV gamma -rays were measured for a number of elements in the region 29 less th an or equal to Z less than or equal to 82 at scattering angles 90, 60, 45 a nd 30 degrees employing a reflection geometry set up and a graded shielding arrangement. A 6 cm(3) HPGe detector was used to detect the scattered gamm a -rays. All the 49 cross sections reported in this payer constitute the fi rst experimental measurement and serve to fill the existing gaps in the cro ss-section data. The comparison of the measured cross sections with Klein-N ishina theory shows electron binding effects becoming significantly large a t small scattering angles and for high Z elements. Incoherent scattering fu nctions S(x, Z), corresponding to momentum transfer values 3.395, 2.4, 1.84 and 1.242 Angstrom (-1) were extracted from the measured cross sections an d were compared with the theoretical predictions. The non-relativistic Hart ree-Fock theory is found to be comparatively better than the Thomas-Fermi m odel. At small momentum transfer values and for high Z elements experimenta l values deviate more from Hartree-Fock theory also suggesting the need for a more rigorous second-order S-matrix calculations. (C) 2001 Elsevier Scie nce Ltd. All rights reserved.