Neutron detection with proton recoil

Nuclear track detectors can also be used to indirectly detect fast neutrons. Fast neutrons interact with the base material of a special film and cause recoil protons to be released. These protons then cause damage tracks in the film which can be made visible and counted as described above. The number of tracks can be used to determine the neutron dose. 

Detection of neutrons by proton recoil is based on collisions of neutrons with protons and subsequent detection of the moving proton. Since neutrons and protons have approximately the same mass, a neutron may, in one collision, transfer all its kinetic energy to the proton. However, there is a possibility that the struck proton may have any energy between zero and the maximum possible, as a result of which the relationship between a neutron energy spectrum and a pulse-height distribution of the struck protons is not simple. It is the objective of this section to derive a general expression for this relationship. The sections that follow show its application for specific detectors. 

Effect of carbon recoils. Neutrons detected by methane-filled counters collide not only with hydrogen nuclei but also with carbon atoms. The ionization produced by carbon recoils is indistinguishable from that produced by protons. However, carbon recoils produce pulses that are smaller than those from protons because of differences in both kinematics and ionization ability. The maximum fraction of neutron energy that can be imparted to a carbon nucleus in one collision is 0.28 (versus 1 for a hydrogen nucleus), and the relative ionization efficiency of a carbon to a proton recoil is about 0.5. Thus, the effect of carbon recoils is to add pulses at the low-energy region of the response... 

Energetic (fast) neutrons interacting with hydrogen produce proton scattering, sometimes called "proton recoil". The scattered proton causes ionization, and may be detected in order to detect fast neutrons. 

Silicon semiconductor detectors for nuclear radiation monitors of neutron rays have been developed by Kitaguchi et al. (1995,1996). These are diffused p-n junction-type devices with low leakage current coated on the surface of the B-containing sensor element. Neutrons were detected as recoil protons by interaction of the proton radiator and a-particles generated by the nuclear reaction °B (n, a) Li. The energy response of this radiation detector meets the standard recommendations and is suited as an area monitor and a personal dosimeter as well. 

---