Analysis of pumping mechanisms affecting the gain of theJ=0-1 andJ=2-1 lines in neonlike selenium

We present collisional-radiative-equilibrium (CRE) gain calculations for the important J=2-1 and J=0-1 3p-3s transitions of neonlike selenium using an extensive set of accurate excited-state couplings and self-consistently calculated ionization and excited-state abundances. An atomic model was put together containing all the most significant processes impacting the gain calculation of these transitions in order to determine the sensitivity of the gain ratio of the J=0-1 to the J=2-1 lines to the monopole excitation cross sections in CRE. It is seen that variations of a factor of 2 or 3 of these cross sections are all that are needed to reverse the calculated J=0-1 to J=0-2 gain ratios. For example, a decrease in the direct excitation rate from the ground to the (1/2,1/2)₀, 3p level by a factor of 3 is sufficient to reverse the gain ratio for the J=0-1 line at 182 {} to the J=2-1 line at 210 {} and move it into agreement with the experimentally observed ratio for these transitions. Experimental observations would suggest that for low-Z elements (Cu, Zn) this ratio is larger than 1, while for high-Z elements (Mo, Sr) it is less than 1. At issue is where the crossover occurs. We draw attention to another instance where the discrepancy between theoretically calculated behavior and experimental behavior can be attributed to the large size of the calculated monopole excitation rate. We also present the calculated temperature and density behavior of the J=0-1 and J=2-1 gains and discuss how this behavior might be used to determine the adequacy of present atomic models to explain experimental neonlike x-ray-laser observations.