  A construction of a thermal neutron testing detector with a thin
[ZnS(Ag)+$^6$LiF] scintillator is described. Results of an investigation of
sources of the detector pulse origin and the pulse features in a ground and
underground conditions are presented. Measurements of the scintillator own
background, registration efficiency and a neutron flux at different objects of
the BNO INR RAS were performed. The results are compared with the ones measured
by the $^3$He proportional counter.
