  Neutron-rich light nuclei and their reactions play an important role for the
creation of chemical elements. Here, data from a Coulomb dissociation
experiment on $^{20,21}$N are reported. Relativistic $^{20,21}$N ions impinged
on a lead target and the Coulomb dissociation cross section was determined in a
kinematically complete experiment. Using the detailed balance theorem, the
$^{19}\mathrm{N}(\mathrm{n},\gamma)^{20}\mathrm{N}$ and
$^{20}\mathrm{N}(\mathrm{n},\gamma)^{21}\mathrm{N}$ excitation functions and
thermonuclear reaction rates have been determined. The
$^{19}\mathrm{N}(\mathrm{n},\gamma)^{20}\mathrm{N}$ rate is up to a factor of 5
higher at $T<1$\,GK with respect to previous theoretical calculations, leading
to a 10\,\% decrease in the predicted fluorine abundance.
