“…Both cases of disk-shaped sources (Hubbell et al, 1961;Epstein and Hubbell, 1963) and rectangular sources (Hubbell et al, 1960) have been systematically studied. Many authors, most of them relying on Hubbell's basic treatment, developed particular aspects of disk sources (Kalla and Al-Saqabi, 1991;Timus and Srivastava, 1997), ring-shaped sources (Timus and Galatanu, 1989;Timus et al, 2000) and rectangular sources (Kalla, 1993;Timus, 1993). Also, a new method for extended gamma source modeling using multipole expansions has recently been elaborated (Loussaief et al, 2006).…”