  This letter explains a new, highly sensitive method for the detection of
neutrons, which uses the T$_{1/2}=845$ ns delay in the decay of $^{128}$I at
the 137.8 keV energy level, resulting from the capture of thermal neutrons by
iodine nuclei in NaI and CsI scintillation detectors. The use of delayed
coincidence techniques with a several $\mu {\rm s}$ time frame for delayed
events allows for the highly effective discrimination of neutron events from
any existing background signals. A comparison of ambient neutron measurements
between those identified through the suggested method from a cylindrical, \o$\,
63 \, {\rm mm}\times 63\, {\rm mm}$ NaI(Tl) scintillator and those from a
low-background proportional $^3$He counter experimentally demonstrates the
efficacy of this neutron detection method. For an isotropic, $4\pi$, thermal
neutron flux of 1 ${\rm n}\, {\rm cm}^{-2}\, {\rm s}^{-1}$, the absolute
sensitivity of the NaI detector was found to be $6.5 \pm 1\, {\rm counts}\,
{\rm s}^{-1}$ with a background of $0.8\, {\rm events}\, {\rm day}^{-1}$ and a
delay time frame of $\Delta {\rm t}=1\, \mu $s. The proposed method can provide
low-background experiments, using NaI or CsI, with measurements of the rate and
stability of incoming neutron flux to a greater accuracy than 10$^{-8}\, {\rm
n}\, {\rm cm}^{-2}\, {\rm s}^{-1}$.
