Measurement of coherent scattering cross-sections of gamma rays at very low momentum transfer

The coherent scattering cross-sections of gamma rays were measured for C, Al, Cu, Sn, Hg, Pb, Bi and Th at very low momentum transfers (in the range of 0.015 to 0.12 mc) using 145 keV photons obtained from a radioactive 141Ce source. The results obtained for high Z elements are then compared with the results obtained from Hartree-Fock-Slater (HFS) form factor calculations and those obtained by Hauser and Mussgnug. Hauser and Mussgnug observed large experimental departures from the form factor values for same high Z elements. However, the present measurements do not confirm the findings of Hauser and Mussgnug. Further as the previously available experimental data at low momentum transfers for low Z elements are not adequate to compare with the form factor values, the present measurements give us an opportunity to check the experimental observations with HFS form factor values. The comparison reveals that the HFS form factor calculations are generally in good agreement at very low momentum transfers for all elements under investigation. (Auth.)