A statistical equilibrium radiative transfer code, RADEX, is made available for public use as part of the Leiden Atomic
and Molecular Database (LAMDA). RADEX is a
one-dimensional non-LTE radiative transfer code,
that uses the
formulation assuming an isothermal and homogeneous medium without large-scale velocity fields.
RADEX is comparable to the LVG method and provides a useful tool in rapidly analyzing a
large set of observational data providing constraints on physical conditions, such as density and
RADEX provides an alternative to the widely used rotation diagram method which relies upon the availability of many optically
thin emission lines and is useful only in roughly constraining the excitation temperature in addition to the column density.
RADEX makes no extrapolation of collisional rate coefficients outside the temperature range specified in the
molecular data file used as input. Instead they are kept constant.
RADEX is offered both as a on-line version for quick estimations of physical conditions, and as source code for extensive grids of calculations.
The formalism adopted in RADEX is summarized in
Van der Tak, F.F.S., Black, J.H., Schöier, F.L., Jansen, D.J., van Dishoeck, E.F. 2007, A&A 468, 627