Neutron Backscatter Technique
A survey method where water content (or more specifically hydrogen content) is established by neutron backscatter.
A radioactive source (Am 241/Be or Cf 252) emits high energy neutrons into the insulation. The neutrons are slowed down or “moderated” by collisions with light elements, in particular hydrogen. They then diffuse back to a thermal neutron detector where the slow neutrons are counted. Moisture in, for example, insulation increases the density of hydrogen nuclei so the number of slow neutrons detected will rise.
CPN Hydrotector in Field Use
FORCE Moisture Probe
General inspection capabilities
Detects moisture under thermal insulation on pipework or vessels. Detection method also works on metal clad insulation. Effective moisture detection capability even where insulation is several centimetres thick.
Hand operated instrument giving on-line readout of results within a few seconds for each location. Detector is sensitive to presence of hydrogen so can be used to detect presence of oil and other liquids with a high hydrogen content.
Detector is very sensitive to water very close and almost completely insensitive to the presence of water farther away. This means that any water within the pipe or vessel will not effect the results. This claim is made by FORCE’s Moisture Probe only.
Inspection limitations
Specialist training is required to operate instrument.
• Not suited for outdoors use during rainfall.
• Needs section of “dry” insulation to calibrate instrument.
• Not suited for use on foam insulation and plastic cladding or any insulation
with high hydrogen content.
• Sensitivity drops very steeply after approximately 50 mm. Therefore has reduced capability for very thick insulation.
• Radiological hazards associated with use of neutron source.
