LUDLUM provides portable neutron meters with a cadmium-located polyethylene sphere surrounding a 3He detector of various sizes (according to the purpose of the meter).
The neutron detector is designed to detect thermal and fast neutrons . Neutrons are detected indirectly through nuclear reactions, which result in energetically charged particles.
Neutron Meters

Model 30-7 Series
Lightweight Digital Neutron Survey Meter Small & Light 19.5 cm (7.7 in.) REM Ball

Model 12-4-7
Neutron Dose Survey Meter Smaller, Lighter 7-inch Polyethylene Ball Gamma Rejection up to 0.1 Sv/h (10 R/hr)

Model 30-4
Low-Weight Device Substitutes for Ratemeter 22.9 cm (9.0 in.) REM Ball

Model 12-4
Moderated Neutron Detector 22.9 cm (9.0 in.) REM Ball Gamma Rejection up to 0.1 Sv/h (10 R/hr)

Model 2241-4
Digital Scaler-Ratemeter Model 42-31H 3He Proportional Detector Ratemeter with Built-in Scaler Function

Model 375-31H
Area Monitor with Neutron Detector 3He Proportional Detector 48-Hour Battery Backup

Model 2363 with 42-41L
Neutron and Gamma Detection Analog + Digital Scaler-Ratemeter External Model 42-41L PRESCILA Detector Internal GM Detector

Model 15
Neutron and Alpha-Beta-Gamma Detection 4-Range Analog Meter Model 42-14H 3He Proportional Detector