Question 5 of 10: Types of Neutron Detectors

Question 5: Types of Neutron Detectors (3 marks)

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Neutron-porosity tools count either thermal or epithermal neutrons returning to a detector after being slowed (moderated) by collisions with hydrogen in the formation; three detector technologies are used commercially:

• Helium-3 (³He) proportional counters. The most common modern detector; a ³He-filled gas tube produces an ionization pulse when a thermal/epithermal neutron is captured (³He + n → ³H + ¹H), with good sensitivity and gamma-ray discrimination.
• Boron trifluoride (BF₃) proportional counters. An older gas-filled detector technology using the ¹&sup0;B(n,α)&sup7;Li capture reaction; largely superseded by ³He but still found in some sondes.
• Scintillation detectors (e.g., lithium-iodide, LiI(Eu)). A solid scintillator crystal doped to capture neutrons and produce a light pulse counted by a photomultiplier tube; used where a compact, rugged solid-state detector is preferred over a pressurized gas tube.