Gamma-rays other processes

After the ko method was introduced (Simonits et al. 1975), the development of the method required many years of hard work. The ko values were accmately measmed for the gamma rays of 112 nuclides (Simonits et al. 1980 Moens et al. 1984 De Corte et al. 1989a) produced by neutron irradiation, as were other activation and decay properties (De Corte et al. 1989a De Corte and Simonits 1989 De Corte et al. 1989b). The model for the activation process needed to take into account the complex neutron spectrum of any research reactor. Initially, the ko method was seen mainly as a method for modeling the activation process. Of course, the gamma-ray detection process is equally important and the models for it are much more... 

Neutron Activation Analysis Few samples of interest are naturally radioactive. For many elements, however, radioactivity may be induced by irradiating the sample with neutrons in a process called neutron activation analysis (NAA). The radioactive element formed by neutron activation decays to a stable isotope by emitting gamma rays and, if necessary, other nuclear particles. The rate of gamma-ray emission is proportional to the analyte s initial concentration in the sample. For example, when a sample containing nonradioactive 13AI is placed in a nuclear reactor and irradiated with neutrons, the following nuclear reaction results. 

The numerical combination of protons and neutrons in most nuclides is such that the nucleus is quantum mechanically stable and the atom is said to be stable, i.e., not radioactive however, if there are too few or too many neutrons, the nucleus is unstable and the atom is said to be radioactive. Unstable nuclides undergo radioactive transformation, a process in which a neutron or proton converts into the other and a beta particle is emitted, or else an alpha particle is emitted. Each type of decay is typically accompanied by the emission of gamma rays. These unstable atoms are called radionuclides their emissions are called ionizing radiation and the whole property is called radioactivity. Transformation or decay results in the formation of new nuclides some of which may themselves be radionuclides, while others are stable nuclides. This series of transformations is called the decay chain of the radionuclide. The first radionuclide in the chain is called the parent the subsequent products of the transformation are called progeny, daughters, or decay products. 

A sample from a suspected nuclear incident is processed by gamma-ray spectral analysis. The sample does not contain any "Mo, or at least none is observed. Also, the sample contains large amounts of 60Co and 137Cs but no other radionuclides detectable by gamma-ray emission. What do you conclude ... 

The Kinds of Nuclear Reactions. Many different kinds of nuclear reactions have now been studied. Spontaneous radioactivity is a nuclear reaction in which the reactant is a single nucleus. Other known nuclear reactions involve a proton, a deuteron, an alpha particle, a neutron, or a photon (usually a gamma ray) interacting with the nucleus of an atom. The products of a nuclear reaction may be a heavy nucleus and a proton, an electron, a deuteron, an alpha particle, a neutron, two or more neutrons, or a gamma ray. In addition, there occurs the very important type of nuclear reaction in which a very heavy nucleus, made unstable by the addition of a neutron, breaks up into two pans of comparable size, plus several neutrons. This process of fission has been mentioned in Chapter 25 and, is described in a later section of the present chapter. 

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