Experimental observation of Z-dependence of saturation depth of 0.662 MeV multiply scattered gamma rays Gurvinderjit Singh, Manpreet Singh, Bhajan Singh, B.S. Sandhu * Physics Department, Punjabi University, Patiala 147 002, India Received 6 March 2006; received in revised form 10 May 2006 Available online 12 July 2006 Abstract The gamma photons continue to soften in energy as the number of scatterings increases in the sample having finite dimensions both in depth and lateral dimensions. The number of multiply scattered photons increases with an increase in target thickness and saturates at a particular value of the target thickness known as saturation depth. The present experiment is undertaken to study the effect of atomic number of the target on saturation depth of 0.662 MeV incident gamma photons multiply scattered from targets of various thicknesses. The scattered photons are detected by an HPGe gamma detector placed at 90° to the incident beam direction. We observe that with an increase in target thickness, the number of multiply scattered photons also increases and saturates at a particular value of the target thickness. The saturation depth decreases with increasing atomic number. The double Compton scattered peak is also observed in the experimental spectra. Ó 2006 Elsevier B.V. All rights reserved. PACS: 32.80.Cy; 13.60.Fz; 78.70.g Keywords: Multiple Compton scattering; Intensity distribution; Saturation depth; Double scattered peak 1. Introduction A correct evaluation of the Compton profile requires that the photon scattered by a sample should have under- gone only one Compton collision. In actual experiments, the interactions of photons with the target result in a signif- icant fraction of multiply scattered photons in addition to singly scattered ones. The energy spectrum of such photons is broad and never completely separate from the singly scattered distribution in observed measurements. This leads to the smearing of information associated with the intensity change of scattered photons, since the singly scat- tered distribution comes from the overlap volume defined by the intersection of the incoming beam and the detector collimation, while the multiply scattered photons practi- cally may come from the whole sample. Photons continue to soften in energy as the number of scatterings increases in the sample. Thus, an accurate measurement of intensity distribution of multiply scattered photons is required in various materials as a function of target thickness to cor- rect the data for multiple scattering contaminations. A complete survey of analytical and Monte Carlo simu- lation approaches to study the multiple scattering has been given in our previous measurement [1], to which one may refer for the literature on this study. The experimental measurements of Williams and Halonen [2] and of Halonen et al. [3] provide intensity and spectral distributions of the double scattering in aluminium with different sample thick- nesses for 59.54 keV incident photons scattered through 150°. Halonen and Williams [4] calculated the angular dis- tribution of the double scattering for aluminium and nickel using the relativistic Klein–Nishina cross-section and applied these results to experimental Compton profiles of aluminium and nickel measured at 60 and 159 keV in order to correct for multiple scattering. Pitkanen et al. [5] have 0168-583X/$ - see front matter Ó 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2006.05.019 * Corresponding author. Tel.: +91 172 98728 09265; fax: +91 175 2286412. E-mail addresses: balvir@pbi.ac.in, balvir99@indiatimes.com (B.S. Sandhu). www.elsevier.com/locate/nimb Nuclear Instruments and Methods in Physics Research B 251 (2006) 73–78 NIM B Beam Interactions with Materials & Atoms