Radionuclides beta decay

Radon-222, a decay product of the naturally occuring radioactive element uranium-238, emanates from soil and masonry materials and is released from coal-fired power plants. Even though Rn-222 is an inert gas, its decay products are chemically active. Rn-222 has a a half-life of 3.825 days and undergoes four succesive alpha and/or beta decays to Po-218 (RaA), Pb-214 (RaB), Bi-214 (RaC), and Po-214 (RaC ). These four decay products have short half-lifes and thus decay to 22.3 year Pb-210 (RaD). The radioactive decays products of Rn-222 have a tendency to attach to ambient aerosol particles. The size of the resulting radioactive particle depends on the available aerosol. The attachment of these radionuclides to small, respirable particles is an important mechanism for the retention of activity in air and the transport to people. 

One prominent and well-known kind of nuclear component is that which is produced by the decay of naturally occurring radionuclides (see Table 1). The best- and longest-known examples are He, produced by alpha decay of the natural isotopes of uranium and Th, and " Ar, produced in one branch of the beta decay of " K. (There are several other natural radionuclides which produce He by alpha decay, but whether because of low parent abundance and/or very slow decay, only in very unusual samples is the production of He not strongly dominated by uranium and thorium.) Since radioactive decay laws are well known, the ratio of daughter to parent isotope(s) in a closed system is a simple function of time, whence this phenomenon has been long and extensively exploited as a geochronometer (e.g., see Chapter 1.16). 

There are five radionuclides whose decay is accompanied by significant beta emissions these are Ra, Ac, Pb, Bi and ° T1. 

Some nuclei undergo radioactive decay by capturing an electron from the A or L shell of the atomic electron orbits. This results in the transformation of a proton to a neutron, the ejection of an unobservable neutrino of definite energy, and the emission of an x-ray where the electron vacancy of the or L shell is filled by an atomic electron from an outer orbit. Because the net change in the radionuclide species is from atomic number Z to Z — 1, similar to the nuclide change from positron emission, electron capture generally competes with all cases of positron beta decay. 

More than 300 different nuclides have been observed as the primary products of fission. The term fission products usually refers to the primary fission products, i.e., the fission fragments and their daughters resulting from radioactive decay and neutron absorption. Only a few of the primary fission products are stable, the rest being beta-emitting radionuclides. As a fission-product radionuclide undergoes beta decay, its atomic number increases whereas its mass number remains constant. The direct yield of a fission-product nuclide is the fraction of the total fissions that yield this nuclide, essentially as a direct-fission fragment. The cumulative... 

The typical curve of beta-particle attenuation in aluminum absorbers, shown in Fig. 2.6, at lower energies resembles the exponential attenuation observed for gamma rays (see Section 2.4.4). The final part of the line curves downward to reach the distinct range associated with Fmax- Attenuation curves for the various beta-decay radionuclides differ because of the different beta-particle energy spectra, but both the characteristic range and the approximately exponential attenuation have been used to estimate maximum beta-particle energies (Evans 1955). 

Technetium-99 is a fission-product radionuclide that is analyzed widely in the environment and in radioactive waste. Because of its long (213,000-y) half-life and high fission yield (6.1%), it can remain at detectable levels after shorter-lived radionuclides have decayed. The emitted low-energy, beta particles (0.294 MeV, maximum) are usually measured by LS counting after purification to remove other radionuclides and interfering salts. "Tc also is measured with proportional counters (see Section 6.4.1) or by ICP-MS (see Section 17.8). 

Calibration curves for this method were constructed by use of single beta transitions only. Further tests of the method were necessary to determine the usefulness of the procedure for measurement of samples that contain radionuclides that emit X-rays, gamma rays, auger and compton electrons, and alpha particles. Table 1 compares those efficiencies predicted from the channels ratio calibration curves with the actual counting efficiencies for several radionuclides which decay by various means. Efficiencies obtained by counting with the wide-beta counter are listed for comparison. The predicted results are in good agreement with the actual efficiencies except in the case of and to a lesser... 

Another situation occurs as a result of an (n,y) reaction, in which an intermediate radionuclide decays to the product of interest. This route is followed to make for example, with the Xe(n, y) Xe process. The neutron capture product Xe beta decays to with a 16.9 h half-life. Because the final product can be chemically separated from the target, specific activity may approach the theoretical value for the pure radionuclide. Obviously, the use of high chemical purity targets and processing reagents is necessary to avoid introducing stable nuclides of the same element as the product. In the example, this means that both the... 

Nuclides of an element that have the same number of protons but different number of neutrons are called isotopes of that element. Some nuclides are stable but many are not these are called radionuclides. The process of transformation is called decay. Radionuclides may decay by emitting an electron, i.e., a beta particle, or photons (gamma or X rays) or an alpha particle consisting of two protons and two neutrons. These processes are termed radioactivity. There can be several different isotopes for an element. Different isotopes are indicted by the symbol for the element with the atomic mass number for the isotope. For example, the important radioactive isotopes of iodine (I) are I, I, I, and I. Each of these isotopes will act the same chemically but can be considerably different radiologi-cally. I and 1-131 are the two common ways of indicating a particular isotope. 

Tritium (H-3) and carbon-14 (C-14) are also volatile radionuclides but H-3 has a short half-life (12.3 yr) and its low beta decay energy (18.5 keV) makes it a relatively mild... 

The decay scheme for a single beta-emitting radionuclide is part of this energy parabola with just the two components of parent and daughter. Figure 1.7 shows the simple case of Cs. Here, some beta decays (6.5 % of the total) go directly to the ground state of most... 

A method for estimating the residence time of tropospheric aerosol particles associated with radon decay product radionuclides is based on the radioactivity of a pair of genetically related radioisobars, such as Pb, Bi or Pb, Po according to the sequential disintegrations in the beta decay scheme, as... 

When the nucleus of a radionuclide releases an alpha or beta particle, an atom of a new element is formed. For example, carbon-14 and iodine-131 both undergo beta-decay, which can be described by the following nuclear equations ... 

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. 

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