Relativistic effects in photoionization

Conference · Sat Dec 31 04:00:00 EST 1994

OSTI ID:199590

Pratt, R H ^[1]

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1. Univ. of Pittsburgh, PA (United States)

The author asks what further information is accessible when photoionization is studied at higher energies, as in the x ray and {gamma}-ray regimes. For a {open_quotes}complete{close_quotes} experiment it is in fact not generally sufficient, even at low energy, to determine the energy dependence of the usual dipole parameters. Rather, such parameters should be determined for each multipole or, alternatively, the energy and angle dependence of angular distributions and polarization correlations. However, it is known that in some circumstances, particularly for total cross sections from s-subshells, relativistic and higher multipole contributions tend to cancel well into the {gamma}-ray regime, leaving a non relativistic dipole description useful. Conversely, it has been shown that in some circumstances quadrupole effects remain of some importance at low energy in angular distributions, even for light elements and even at threshold. In general, and neglecting small relativistic effects, except for bound state normalization the high energy photoeffect matrix element is given by the matrix element in the nuclear point Coulomb potential. Consequently, at all energies the dependence of the photoionization matrix element on atomic properties is given by dipole and quadrupole terms, plus small octupole contributions, within an accuracy of 1%. This result, demonstrated within independent particle approximation, is expected to remain valid when many-electron correlations are included.

• OSTI ID: 199590
• Report Number(s): CONF-941129--
• Country of Publication: United States
• Language: English

Related Subjects

66 PHYSICS
ATOMS
ENERGY DEPENDENCE
GAMMA RADIATION
MULTIPOLES
PHOTOIONIZATION
X RADIATION