# PopRatio: A program to calculate atomic level populations in astrophysical plasmas

## Description

Abstract We describe a Fortran 90 program to calculate population ratios of atomic levels. The program solves the equations of statistical equilibrium considering all possible bound-bound processes: spontaneous, collisional or radiation induced (the later either directly or by fluorescence). There is no limit on the number of levels or in the number of processes that may be taken into account. The program may find a wide range of applicability in astronomical problems, such as interpreting fine-struct... Title of program: PopRatio Catalogue Id: ADNZ_v1_0 Nature of problem The purpose of this program is to calculate population ratios of atomic levels. The excited level population ratios may be used to infer the physical conditions from observed fine-structure absorption lines or collisionally excited emission lines (such as coronal emission lines). Another possible use is in calculating cooling rates due to collisional excitation of low-lying levels. Versions of this program held in the CPC repository in Mendeley Data ADNZ_v1_0; PopRatio; 10.1016/S0010-4655(01)00149-7 This program has been imported from the CPC Program Library held at Queen's University Belfast (1969-2019)