I know some neutron detectors use two GM tubes with one having a neutron capturing foil and rely on the differential measurements as a form of neutron detection. I see they can be effective as merely a detector of neutrons - since the neutron activated foil will leave one GM tube with higher activity reading than the other (but even so not for continuous beams of unknown, possibly high, neutron/gamma fluxes).Use two GM tubes, only one with silver foil, one without, and measure the difference.
Use variant of above detector. If neutrons are all thermal, then no moderator is required. BF3 or He3 detectors are good choices. For high fluxes, maybe an ion-chamber enhanced with silver foil will work.
However I am wondering as to their true effectiveness in a fluctuating high gamma and neutron radiation background since the gamma may saturate the signals of both GM tubes rendering differential readings ineffective? Also, unless they are in some kind of high density dual GM tube array, would such a detector (if they only have two GM tubes) not be very directionally dependent in their detection?
I thought most of the differential GM tube detectors with the activation foil tend to have a UHMWPE outer shell as neutron moderators to thermalize the neutrons first to improve effectiveness of activating the foil?