Neutron fast’/high-energy, bombardment

The effects of high-energy bombardment of solids have been studied intensively in the last decade by many investigators (/). Large changes in the physical properties of materials are observed particularly upon fast massive particle irradiation, for example, by fast neutrons in a nuclear reactor, which results in the displacement of the atoms from their normal lattice positions. 

High-energy (or fast ) neutrons are produced by the nuclear fission of 92U and have energies of 1 MeV (see Section 2.5). The bombardment of sulfur-32 with fast neutrons (equation 2.12) gives an artificial isotope of phosphorus, but 15P has a half-life of 14.3 days and decays by P-particle emission (equation 2.13). 

Briefly, the experimental procedure consists of bombarding a target of, say, triton with a beam of protons from an accelerator (see Fig. 9.1). The ensuing reaction, as indicated in the above equation, produces high-energy neutrons (in the order of 1 Mev). If the proton beam is applied intermittently, the target will yield bursts of fast neutrons, and some of these in turn will produce neutron-flux transients in a test specimen placed in the vicinity of the target. The time variations in neutron... 

Nuclear reactors (Section 26-15) are also used as neutron sources. Neutrons ejected in nuclear reactions usually possess high kinetic energies and are called fast neutrons. When they are used as projectiles they cause reactions, such as (w, p) or ( , a) reactions, in which subsidiary particles are ejected. The fourth missing element, number 61 (promethium), was synthesized by fast neutron bombardment of neodymium-142. 

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