SHORT WAVELENGTH LASER CALCULATIONS IN THE Be I, B I AND C I ISOELECTRONIC SEQUENCES

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Abstract
Short Wavelength Laser Calculations in the Beryllium, Boron and Carbon Isoelectronic Sequences - Level populations of the 2s3p, 2s23p 2 and 2s22p3p configurations in ions of the Be I, B I and C I isoelectronic 2 sequences can be inverted with respect to populations of the 2s3s, 2s23s, and 2s22p3s configurations by electron collisional pumping. In the case of B I and C I ions, the process is analogous to the process for Ne-like ions which has lately received considerable attention. In the case of Be I ions, the inversion is a consequence of the slow radiative decay of the 2s3p 3P2 and 2s3p 3P0 levels. Level populations are calculated for Be-like, B-like and C-like ions with atomic number Z between 18 and 36 and for electron densities from 1015 to 1022 cm-3. For each of the Be I and B I isoelectronic sequences, 20 levels are involved with principal quantum number n equal either to 2 or 3. For the CI isoelectronic sequence 46 levels are involved. Using the level populations, gain coefficients are calculated for transitions of the type 2s3s - 2s3p, 2s23s - 2s23p and 2s22p3s - 2s22p3p. The calculated gain coefficients are compared to previous calculations. At high electron densities where collisional mixing of the excited levels becomes important, the intensities of the X-ray transitions from the 2sk2pm3p levels decrease relative to the X-ray transitions from the 2sk2pm3s and 2sk2pm3d levels where k=1, m=0 or k=2, m=0,1. The density dependence of these X-ray line ratios is calculated elsewhere /16, 17/. These line ratios represent a promising diagnostic for electron density. Finally, the opacities of the 2s2p - 2s3s, 2s22p - 2s23s and 2s22p2 - 2s22p3s transitions are discussed for plasma parameters for which a reasonable gain can be achieved

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