The radiation detectors mentioned previously detect radiation by physical and chemical interaction with the substance of the detector. Neutrons, however, have only scattering interactions and initiate nuclear reactions with the nuclei; thus, the detection of the neutrons is problematic and have only a small amount of efficiency.

The nuclear reactions can be used for the detection and measurement of neu­trons. Two nuclear reactions are mentioned: 10B(n, a)7Li and 6Li(n, a)3H. Boron and lithium are present in the form of boron trifluoride or lithium glass, respectively. In both cases, the emitted alpha particles are detected. The intensity of the alpha radia­tion is proportional to the number of absorbed neutrons. BF3 gas is placed into a proportional counter, i. e., a gas-filled tube is used to detect the alpha particles. In the case of Li-glass, its scintillation property is used up in the detection.

The neutrons are detected by an LiF + ZnS combined detector. In the 6Li (n, a)3H nuclear reactions, two charged particles (the alpha particle and the tritium nucleus) are formed, inducing scintillation of zinc sulfide.