Analytic proof of partial conservation of seniority in image shells

A partial conservation of the seniority quantum number in image shells has been found recently in a numerical application. In this paper an analytic proof for this problem is derived as an extension of the work [L. Zamick, P. Van Isacker, Phys. Rev. C 78 (2008) 044327]. We analyze the properties of the non-diagonal interaction matrix elements with the help of the one-particle and two-particle coefficients of fractional parentage (cfpʼs). It is found that all non-diagonal (and the relevant diagonal) matrix elements can be re-expressed in simple ways and are proportional to certain one-particle cfpʼs. This remarkable occurrence of partial dynamic symmetry is the consequence of the peculiar property of the image shell, where all image and 5 states are uniquely defined.