Nuclides characteristic

Nuclide Characteristic X-rays Energies [keV] Half-life... 

As the plasma moves through the centre of maximum curvature it is forced through the vacumn interface into a space-time domain of inverted chirahty and decreasing pressme. New matter (antimatter) emerges beyond the interface as an equilibrimn mixture of cosmic rays, in a soup of a-particles, as it is squirted out from the black hole into free space. Some of the newly formed nuchdes decay radioactively on moving into regions of lower curvatme and a set of nuclides, characteristic of local cmvatme, smvives. In the solar system the set consists of the 264 stable isotopes of 81 elements described before. The closed periodic sytem of nuclides and anti-nuclides, related by inversion, is consistent with the proposed mode of cosmic circulation of mass. 

NAA is the most common form of activation analysis. The activation reaction is induced by the interaction of a neutron with the nucleus of an analyte element. Depending on the energy of the incident neutron and the reaction cross sections of the target elements, different types of reactions can take place, leading to activation products as described in O Sect. 30.2. This reaction is commonly followed by the measurement of a nuclide-characteristic de-excitation step (radioactive decay). It is this characteristic gamma-ray decay that is commonly used in the detection and determination of the element of interest. 

Croff, A. G., 1983, A Versatile Computer Code for Calculating the Nuclide Compositions and Characteristics of Nuclear Material, Nucl. Technol. 62, p 335, September. 

Element has no stable nuclides the value given in parentheses is the atomic mass number of the isotope of longest known half-life. However, three such elements (Th, Pa and U) do have a characteristic terrestrial isotopic composition, and for these an atomic weight is tabulated. 

Very few nuclides with Z < 60 emit a particles. All nuclei with Z > 82 are unstable and decay mainly by a-particle emission. They must discard protons to reduce their atomic number and generally need to lose neutrons, too. These nuclei decay in a step-by-step manner and give rise to a radioactive series, a characteristic sequence of nuclides (Fig. 17.16). First, one a particle is ejected, then another a particle or a (3-particle is ejected, and so on, until a stable nucleus, such as an iso tope of lead (with the magic atomic number 82) is formed. For example, the uranium-238 series ends at lead-206, the uranium-235 series ends at lead-207, and the thorium-232 series ends at lead-208. 

Each radioactive nuclide has a characteristic, constant half-life. This means that it acts as a clock, ticking ... 

Modeling of the transport of the long-lived nuclides, especially U, require knowledge of the input at the water table as a boundary condition for aquifer profiles. There are few studies of the characteristics of radionuclides in vadose zone waters or at the water table. Significant inputs are likely to occur to the aquifer due to elevated rates of weathering in soils, and this is likely to be dependent upon climatic parameters and has varied with time. Soils may also be a source of colloids and so provide an important control on colloidal transport near recharge regions. 

River inputs. The riverine endmember is most often highly variable. Fluctuations of the chemical signature of river water discharging into an estuary are clearly critical to determine the effects of estuarine mixing. The characteristics of U- and Th-series nuclides in rivers are reviewed most recently by Chabaux et al. (2003). Important factors include the major element composition, the characteristics and concentrations of particular constituents that can complex or adsorb U- and Th-series nuclides, such as organic ligands, particles or colloids. River flow rates clearly will also have an effect on the rates and patterns of mixing in the estuary (Ponter et al. 1990 Shiller and Boyle 1991). 

In terms of atomic spectrometry, NAA is a method combining excitation by nuclear reaction with delayed de-excitation of the radioactive atoms produced by emission of ionising radiation (fi, y, X-ray). Measurement of delayed particles or radiations from the decay of a radioactive product of a neutron-induced nuclear reaction is known as simple or delayed-gamma NAA, and may be purely instrumental (INAA). The y-ray energies are characteristic of specific indicator radionuclides, and their intensities are proportional to the amounts of the various target nuclides in the sample. NAA can thus... 

De-excitation of 99mTc has specific features. This nuclide decays with a half-life of 6 hours, but its half-life varies slightly according to environmental conditions [30] or chemical states [31,32], Moreover, the emission probabilities of characteristic X-rays just after the isomeric transition 99mTc — "Tc are influenced by environmental factors [33] which result in a change of the K/VKoc X-ray intensity ratio [34],... 

Studies of short-lived radionuclide generators (4-6) do not adequately treat the quantitative problems of the daughter nuclide elution or those specific to their optimal clinical use. Two essential physical characteristics of a generator are the yield of the daughter nuclide and its radiochemical and radionuclidic purity. To realize the full potential of a short-lived radionuclide generator for medical studies requires that these two characteristics are optimized and are compatible with parameters important to clinical use such as total perfused volume and duration of the scintigraphic examination. 

A most important characteristic of a generator other than the elution yield of the daughter is the extent of contamination of the eluate by the parent nuclide. This contamination is defined as breakthrough which can be calculated as shown in equation (14). Breakthrough is dependent on the distribution... 

Elemental composition cannot be obtained by simple analysis of the radiation since (3 emission is continuous. Thus, 7 emission, which accompanies (3 emission and is characteristic of each nuclide, is analysed. These emissions occur in the same spectral range as X-ray fluorescence. 

Pu may be considered as an ideal tracer nuclide for these studies because of its decay characteristics. Its existence or absence in the early solar system can be considered as a crucial test for or against the theories of the synthesis of chemical elements in stars. 

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