Disintegration by neutrons
The discovery of the neutron placed a very important atom-splitting missile at the disposal of physicists. Apart from a-particles, only two controllable particles had been available for the bombardment of nuclei, namely, the proton and deuteron (heavy hydrogen nucleus). The positive charge on both of these particles enablesthem to be speeded up to high energies by electric fields, but at the sam e time their charge was also a disadvantage. It meant that they were strongly repelled away from nuclei, and consequently very few were able to penetrate nuclei. Owing to the fact that it has no electric charge, the neutron does not possess this disadvantage.
In the early 1930s it was found that the majority of the elements could be successfully disintegrated by neutron bombardment, and many interesting and useful products were obtained. Take the case of lithium-6 for example. If this is struck by a neutron it produces the radioisotope of hydrogen called tritium (iH), which is a beta emitter with a half-life of 12.26 years. In nuclear reactions a neutron is represented by the symbol bn, signifying that it is a particle of mass number one and zero electric charge. We can therefore represent the lithium-neutron reaction thus:
Another interesting case is the action of a neutron on magnesium, which is typical of a number of reactions in which the end-product is identical with the original. On capturing a neutron the magnesium is transmuted into sodium-24, accompanied by the ejection of a proton. The sodium nucleus formed is a radioactive isotope with a half-life of about 15 hours, which eventually decays back into magnesium with the emission of a 1-particle. These reactions are represented as follows:
Irradiation of magnesium by neutrons
Beta decay of the sodium isotope