Bombardment high-energy radiation sources

High-energy radiation may be classified into photon and particulate radiation. Gamma radiation is utilized for fundamental studies and for low-dose rate irradiations with deep penetration. Radioactive isotopes, particularly cobalt-60, produced by neutron irradiation of naturally occurring cobalt-59 in a nuclear reactor, and caesium-137, which is a fission product of uranium-235, are the main sources of gamma radiation. X-radiation, of lower energy, is produced by electron bombardment of suitable metal targets with electron beams, or in a... 

A variety of sources constantly bombard your body with radiation. Your exposure to these sources results in an average annual radiation exposure of 100-300 millirems of high-energy radiation or 0.1-0.3 rems. Table 24.7 shows your annual exposure to common radiation sources. 

In the second type of analysis, high-energy bombardment of soils with neutrons, on the other hand, leads to what is called neutron activation. Reemission of radiation from neutron-activated soil allows for the identification of the elements present. This type of analysis typically requires a source of high-energy neutrons and so requires special equipment [8],... 

For analytical purposes. X-rays are generated in four ways (I) by bombardment of a metal target with a beam of high-energy electrons. (2) by exposure of a substance to a primary beam of X-rays to generate a secondary beam of X-ray fluorescence, (3) by use of a radioactive source whose decay process results in X-ray emission, and (4) from a synchrotron radiation source. Only a few laboratories in the United States have facilities to produce X-rays from synchrotron radiation. For this reason, wc will consider only the first three sourcc.s. 

In the presence of a high-electric-fleld coldcathode, electron emission may be initiated by injecting a plasma into a vacuum gap from an external source or by bombarding either electrode with high-energy electrons, ions, or radiation from, for example, a laser beam. Any of these processes will lead to breakdown and the formation of a vacuum arc. 

Unstable radionuclei result on subjecting the nuclei of some elements to neutron bombardment. During the decay process, in which the radionuclei return to more stable forms, characteristic radiation is emitted. The energy of the radiation is characteristic of the element, and its intensity forms the basis for quantitative elemental analysis. The advantages of NAA for trace analysis include low detection limits, good sensitivity, multi-element capability and relative freedom from matrix effects. However, for successful application of this technique skilled personel are required and because of the low sample throughput the amount of work involved in the analysis of column fractions, for example, is prohibitively high. In addition, it may take up to several weeks before the results are available. Further, only few laboratories have easy access to a neutron source. 

---