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How do radiation detectors measure neutrons?

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detector output connected to a measuring circuit — radiation measurement Figure 1: (A) A simple equivalent circuit for the development of a voltage pulse at the output of a detector. R represents the resistance and C the capacitance of the circuit; V(t) is the time (t)-dependent voltage produced. (B) A representative current pulse due to the interaction of a single quantum in the detector. The total charge Q is obtained by integrating the area of the current, i(t), over the collection time, t_c. (C) The resulting voltage pulse that is developed across the circuit of (A) for the case of a long circuit time constant. The amplitude (V_max) of the pulse is equal to the charge Q divided by the capacitance C.

Neutrons are electrically neutral and do not directly ionize matter, so radiation detectors must rely on nuclear reactions or scattering to convert them into detectable charged particles.12

Slow-Neutron Detection

Slow-neutron detectors utilize reactions with a positive Q-value, where the neutron interacts with a target nucleus (such as boron-10, lithium-6, or helium-3) to produce charged particles. These particles deposit energy in the detector, creating a measurable pulse. Common technologies include:1
* Proportional counters: Tubes filled with gases like boron trifluoride or helium-3.1
* Scintillators: Materials incorporating boron or lithium that produce light flashes when struck by reaction products.13
* Fission chambers: Ion chambers lined with fissionable material like uranium-235, used for monitoring intense neutron sources.1

Fast-Neutron Detection

Fast neutrons are detected primarily through elastic-scattering interactions with hydrogen nuclei. The resulting recoil protons are charged and can be detected in hydrogenous gas-filled proportional counters or organic scintillators. Because fast-neutron cross sections are low, detectors are sometimes surrounded by a moderator to slow the neutrons down for easier counting.2