Electron-capture decay results

For many of the analytical techniques discussed below, it is necessary to have a source of X-rays. There are three ways in which X-rays can be produced in an X-ray tube, by using a radioactive source, or by the use of synchrotron radiation (see Section 12.6). Radioactive sources consist of a radioactive element or compound which spontaneously produces X-rays of fixed energy, depending on the decay process characteristic of the radioactive material (see Section 10.3). Nuclear processes such as electron capture can result in X-ray (or y ray) emission. Thus many radioactive isotopes produce electromagnetic radiation in the X-ray region of the spectrum, for example 3He, 241Am, and 57Co. These sources tend to produce pure X-ray spectra (without the continuous radiation), but are of low intensity. They can be used as a source in portable X-ray devices, but can be hazardous to handle because they cannot be switched off. In contrast, synchrotron radiation provides an... 

Beta decay is a general term applied to radioactive decay processes that result in the mass number A remaining constant while the atomic number Z changes. There are three types of beta decay beta-minus (/3 ) decay, positron (/3+) decay, and electron capture decay. It should be mentioned that (3 decay is often referred to as just beta decay, which is not strictly correct, because it is only one type of beta decay. 

Electron Capture Decay. Electron capture decay is a competing process to positron decay and thus results in an increase in the neutron-to-proton ratio in the nucleus. In this process, a bound, inner orbital electron is captured by the nucleus, resulting in the conversion of a proton into a neutron, the emission of a neutrino, and, if the daughter nucleus is left in an excited state, the emission of one or more gamma rays. The net reaction is shown below ... 

The K0 IKa x-ray intensity ratios by photoionization and electron-capture decay have been calculated for several chemical compounds of 3d elements by the use of the discrete-variational Xo (DV-Xa) molecular orbital method. The calculated results indicate that the K/3lKa ratios depend on the excitation mode as well as the chemical effect. For the similar chemical environments the K0 /Ka ratio by photo ionization is larger than that by electron-capture decay, due to the excess 3d electron in the latter case. However, the difference is small, sometimes negligible in comparison with the chemical effect. Possible reasons for large difference in earlier experiments are discussed and future experiments are suggested. 

Emission of an a-particle produces a new nucleus with a reduction in atomic number by two and in mass number by four. When a nucleus emits a /3-particle, the atomic number of the new nucleus increases by one (over that of the decaying nucleus), but the mass numbers are unchanged. Some radioactive nuclei do not increase in atomic number in decay, but decrease by one unit of mass number due to the emission of a positron (a positively charged /3 ray). Eor example, in /3 decay with electron emission, is converted to yN, whereas in positron f3 decay, uNa is converted to i a. An alternative process to f3 decay involves the absorption of an orbital electron by the nucleus in a process known as electron capture, which results in a decrease in the atomic number of the product nucleus, for example, Wu decaying to Pt. Gamma-ray decay results in no change in either mass number or atomic number. 

An interesting application of Mossbauer emission spectroscopy is illustrated by the study of Co(pyridine)2Cl2 which was used as a source against a single-line absorber. The resulting emission spectra clearly reveal the presence of the phase transition and indicate that this polymeric material is able to withstand the damage associated with the electron capture decay of the Co. 

The emission of y rays follows, in the majority of cases, what is known as P decay. In the P-decay process, a radionuclide undergoes transmutation and ejects an electron from inside the nucleus (i.e., not an orbital electron). For the purpose of simplicity, positron and electron capture modes are neglected. The resulting transmutated nucleus ends up in an excited nuclear state, which prompdy relaxes by giving offy rays. This is illustrated in Figure 2. 

Helium is the second most abundant element in the universe (76% H, 23% He) as a result of its synthesis from hydrogen (p. 9) but, being too light to be retained by the earth s gravitational field, all primordial helium has been lost and terrestrial helium, like argon, is the result of radioactive decay ( He from a-decay of heavier elements, " °Ar from electron capture by... 

Normally, in impact ionization, outer electrons are removed. Infrequently, however, an inner electron may be ejected or a K-process may occur such as an orbital electron capture or /3-decay. In such cases, the result is an electronic rearrangement, in preference to emission. Since enough energy is available, frequently the resultant ion is multiply charged. The cross section for this process follows the usual Bethe-type variation -T 1 ln(BT), where B is a constant (Fiquet-Fayard et al., 1968). In charged particle irradiation, the amount of energy lost in the K-processes is very small, usually much less than 1%. On the other hand, some specific effect may be attributable to that that is, experiments can be so designed. 

Electron capture accomplishes the same end result as positron emission, but because the nuclear charge is low, positron emission is the expected decay mode in this case. Generally, electron capture is not a competing process unless Z 30 or so. 

A fourth mode of decay, which results in the nucleus reducing its proton number by one, is called electron capture, whereby a proton from the nucleus captures one of the extranuclear (orbital) electrons, converting itself into a nuclear neutron. The daughter is isobaric (same mass) with the parent, but has a proton number which is decreased by one ... 

Ne-b V. Electron capture is a form of beta decay that results in the atomic number... 

Radioactivity is the spontaneous emission of radiation from an unstable nucleus. Alpha (a) radiation consists of helium nuclei, small particles containing two protons and two neutrons (fHe). Beta (p) radiation consists of electrons ( e), and gamma (y) radiation consists of high-energy photons that have no mass. Positron emission is the conversion of a proton in the nucleus into a neutron plus an ejected positron, e or /3+, a particle that has the same mass as an electron but an opposite charge. Electron capture is the capture of an inner-shell electron by a proton in the nucleus. The process is accompanied by the emission of y rays and results in the conversion of a proton in the nucleus into a neutron. Every element in the periodic table has at least one radioactive isotope, or radioisotope. Radioactive decay is characterized kinetically by a first-order decay constant and by a half-life, h/2, the time required for the... 

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