  Here we investigate ground and metastable negative ion formation in
low-energy electron collisions with the actinide atoms Th, Pa, U, Np and Pu
through the elastic total cross sections (TCSs) calculations. For these atoms,
the presence of two or more open d- and f- subshell electrons presents a
formidable computational task for conventional theoretical methods, making it
difficult to interpret the calculated results. Our robust Regge pole
methodology which embeds the crucial electron correlations and the vital
core-polarization interaction is used for the calculations. These are the major
physical effects mostly responsible for stable negative ion formation in
low-energy electron scattering from complex heavy systems. We find that the
TCSs are characterized generally by Ramsauer-Townsend minima, shape resonances
and dramatically sharp resonances manifesting ground and metastable negative
ion formation during the collisions. The extracted from the ground states TCSs
anionic binding energies (BEs) are found to be 3.09 eV, 2.98 eV, 3.03 eV, 3.06
eV and 3.25 eV for Th, Pa, U, Np and Pu, respectively. Interestingly, an
additional polarization-induced metastable TCS with anionic BE value of 1.22 eV
is created in Pu due to the size effect. We also found that our excited states
anionic BEs for several of these atoms compare well with the existing
theoretical electron affinities including those calculated using the
relativistic configuration-interaction method. We conclude that the existing
theoretical calculations tend to identify incorrectly the BEs of the resultant
excited anionic states with the electron affinities of the investigated
actinide atoms; this suggests a need for an unambiguous definition of electron
affinity.
