Electromagnetic Excitation Rates for Nuclear Isomers in a Hot Dense Plasma

In high neutron flux environments where isomers can be strongly populated by nucleonic reactions, isotope abundances from reaction network chains can be affected by the population of nuclear isomers. At high temperatures and densities, there is the additional possibility of populating these isomers electromagnetically. Here, we examine the rates for electromagnetic excitation of the isotopes of several isomers of interest both in astrophysics and applied physics (e.g., ²³⁵U, ¹⁹³Ir, and ^87,88Y). We consider six possible electromagnetic processes, namely, photoabsorption, inverse internal conversion, inelastic electron scattering, coulomb excitation, and (,') and (e,e') reactions. We find that for plasma temperatures kT ~ 1 to 10 keV, the electromagnetic reactions rates are negligible. Thus, we conclude that reaction network calculations do not need to include the possibility of electromagnetically exciting nuclear isomers. This is true in both stellar and terrestrial thermonuclear explosions, as well as in plasma conditions expected at the National Ignition Facility.