NEUTRON DETECTION AND SPECTROSCOPY

Since neutrons do not directly ionize atoms, they are detected indirectly upon producing a charged particle or a photon, which is then recorded with the help of an appropriate detector. The charged particle or the photon is the result of a neutron interaction with a nucleus. If the mechanism of the interaction is known, information about the neutron can be extracted by studying the products of the reaction. Many types of interactions are used, divided into absorptive and scattering reactions. 

Absorptive reactions are (n, a), (n, p), in,y), or (n, fission). In the case of an (n, y) reaction, the neutron may be detected through the interactions of the gamma emitted at the time of the capture, or it may be detected through the radiation emitted by the radioisotope produced after the neutron is captured. The radioisotope may emit /3 or or y or a combination of them. By counting the activity of the isotope, information is obtained about the neutron flux that produced it. This is called the activation method. If the reaction is fission, two fission fragments are emitted being heavy charged particles, these are detected easily. 

The main scattering reaction used is neutron-proton collision, called the proton-recoil method. The knocked-out proton is the particle recorded. 

With the exception of the proton-recoil method, which functions for fast neutrons only ( 1.0 keV), all the other interactions can be used with neutrons of any energy. However, at every neutron energy, one method may be better than another. The best method will be selected based on the neutron 

This chapter discusses in detail all the neutron detection methods mentioned above, as well as the Bragg crystal spectrometer, the time-of-flight method, compensated ion chambers, and self-powered neutron detectors (SPND). Other specialized neutron detectors, such as fission track recorders and thermoluminescent dosimeters, are described in Chap. 16. 

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