Understanding Neutron Radiography Post Exam Reading VIII-Part 2a of 2A

Neutron Detectors
There are several mechanisms and devices used to detect neutrons of
various energies. Ionization chambers, proportional counters, scintillators,
activation foils, track etch detectors, film emulsions, nuclear emulsions and
thermoluminescent phosphors are some of the many devices used to detect
neutrons. The main mechanisms used to detect neutrons in these devices are
the (n, α), (n, p), (n, d), (n, f) and (n, γ) nuclear reactions.
(n, f ) f= fragments
Proportional Neutron Detectors Many fast and slow neutron counters use
proportional counting chambers filled with boron trifluoride (BF 3 ) gas, often
enriched in boron-10. The interaction of thermal (slow) neutrons with boron
gas releases an alpha particle of several mega electron volts that is easily
detected in the proportional mode. Fast neutrons are detected by a similar
counter, in which thermal neutrons are absorbed in an external cadmium
shield; the fast neutrons that pass through the shield are thermalized in
hydrogen rich material and counted in the proportional chambers.
10
5 B + n → 4 2 He2+ + 7 3 Li + γ
Charlie Chong/ Fion Zhang