Dramatic relativistic effects on the ns dipole angular distribution asymmetry parameter β_ns of high-Z atoms

It is well-known that the dipole angular distribution asymmetry parameter β_ns for photoionization from ns subshells takes a value of 2.0 nonrelativistically for closed shell atoms [1]. However, relativistic effects [2] cause the β_ns deviate from its nonrelativistic value. One such case is Cooper minimum (CM) [3] region, at which the β_ns takes a lower value than 2.0, and is energy-dependent,  because the minima in the relativistic dipole channels, ns→εp_1/2 and ns→εp_3/2, do not energetically coincide [4]. In the present work, we address the question: can β_ns deviate from 2.0 in closed shell atoms due to relativistic effects other than CM? To accomplish the objective, we examine the photoionization parameters of the high-Z elements employing the Dirac-Fock (DF) and relativistic-random-phase approximation (RRPA) methodologies. The photoionization from the 6s subshells of Hg (Z=80), Rn (Z=86), Ra (Z=88), No (Z=102), Cn (Z=112), Og (Z=118) and the 7s subshells of Ra, No, Cn and Og are considered.  The present work concludes that β_ns will asymptotically tend to a value lower than 2.0; the degree of deviation depends upon the phase shift difference of spin-orbit split continuum channels that increases with Z. [1] J. Cooper, and R. N. Zare, J. Chem. Phys. 48, 942 (1968); [2] T. E. H. Walker and J. T. Waber, Phys. Rev. Lett. 30, 307 (1973); [3] J. W. Cooper, Phys. Rev. 128, 681 (1962); [4] S. T. Manson and A. F. Starace, Rev. Mod. Phys. 54, 389 (1982).