  An effective field theory technique that combines the standard nuclear
physics approach and chiral perturbation theory is applied to the $hen$
process, ${}^{3}{He}+n\to {}^{4}{He}+ \gamma$. For the initial and final
nuclear states, high-precision wave functions are generated via the variational
Monte Carlo method using the Argonne $v_{14}$ potential and Urbana VIII
trinucleon interactions, while the relevant transition operators are calculated
up to ${\cal O}(Q^4)$ in HB$\chi$PT. The imposition of the renormalization
condition that the magnetic moments of ${}^{3}{He}$ and ${}^{3}{H}$ be
reproduced allows us to carry out a parameter-free calculation of the $hen$
cross section. The result, $\sigma=(60\pm 3\pm 1) \mu b$, is in reasonable
agreement with the experimental values, $(54\pm 6) \mu b$ and $(55\pm 3) \mu
b$. This agreement demonstrates the validity of the calculational method
previously used for estimating the reaction rate of the solar $hep$ process.
