Nuclides definition

The concept most commonly used when dealing with radioactive nuclides is activity. By definition, the activity of a number of atoms of a nuclide is the number of decay events per unit of time. The law of radioactivity tells us that this activity is equal to the decay constant times the number of atoms. 

Figure 5. A schematic representation of superposed steady-state reservoirs of constant volumes Vi (fractional crystallization is omitted in this schema). At steady-state, Vi/xi=V2/x2=..., where x is the residence time. This is analogous to the law of radioactive equilibrium between nuclides 1 and 2 Ni/Ti=N2/T2=...A further interest of this simple model is to show that residence times by definition depend on the volume of the reservoirs.

Note Care has to be taken when mass values from dated literature are cited. Prior to 1961 physicists defined the atomic mass unit [amu] based on Vie of the mass of one atom of nuclide 0. The definition of chemists was based on the relative atomic mass of oxygen which is somewhat higher resulting from the nuclides and contained in natural oxygen. 

An outstanding feature of inorganic mass spectrometry is its determination of precise and accurate isotopic abundances and isotope ratios. Isotopes of the same element (of the same number of protons or atomic number of element, Z) are, by definition, nuclides with different mass m and mass number A (A = Z + N) due to the different number of neutrons (N) in the nucleus. Isotope analyses are of special interest for characterizing the composition of samples with respect to stable and unstable isotopes in quite different concentration ranges - from the analysis of matrix elements down to the trace and ultratrace concentration level.1-9 Of 1700 isotopes, nearly 16 % (264 isotopes) are stable. The chemical elements Tc, Pm, Th, U and the transuranic elements do not possess stable isotopes. 

The consolidated titanate waste pellets are similar in appearance to their glass counterparts, i.e., both are dense, black and apparently homogeneous. Microscopic analyses, however, reveal important differences between these two waste forms. While little definitive work has been done with glassy waste forms, it is apparent that several readily soluble oxide particulates of various nuclides are simply encapsulated in the glass matrix. The titanate waste form has undergone extensive analyses which includes optical microscopy, x-ray, scanning electron microscopy, microprobe, and transmission electron microscopy (l ) The samples of titanate examined were prepared by pressure sintering and consisted of material from a fully loaded titanate column. Zeolite and silicon additions were also present in the samples. 

I and the shielded nuclide 136Cs correlations have definite curvature. 

The half-life for a given nuclide can be derived from Equation (3.6) when the value of the decay constant is known. In accordance with the definition of the term half-life, when A /A0 = 1 /2, then t = tx /2. Substituting these values into Equation (3.6) gives... 

A radioactive nuclide (radioisotope) is spontaneously converted to another nuclide by one of the processes below each definition is followed by an example. As discussed above, all are accompanied with a loss of mass and a release of energy. 

The negative quantity in brackets is an irrational number known as the golden ratio, t = 0.61803. The solution Z = — iV(1.61803...) = — nuclide stability, as defined on both plots, converges to a point on the line r = Nx = r at A 267, the maxinum possible mass number for nuclides, stable against /1-type decay. By definition, this maximum,... 

More definitions are necessary to attempt this sort of optimization Potential californium is a measure of the maximum amount of californium that can be produced from a given batch of feed, taking into account the fact that many atoms undergo fission along the path from feed to product. The efficiency of a particular irradiation is the amount of californium produced divided by the amount of potential californium consumed in the irradiation and subsequent processing. This efficiency measure takes into consideration the destruction of the 2 2Cf by decay and neutron capture and processing losses of all the nuclides in the chain. 

This nuclear technology is based on both the nuclear and the chemical properties of the atom. At the beginning of the twentieth century fewer than 90 chemical elements were known and there was only a dawning awareness of isotopes. Today, largely because of the nuclear industry, thousands of isotopes (or nuclides, depending on the properties of interest) have been identified. Brief definitions of several chemical and nuclear terms are given in Table 21.1. 

TABLE 21.1 Definitions of Atoms, Chemical Elements, Isotopes, Nuclides, and Isomers... 

The word particle (e.g. nuclide or electron) is used routinely, and has ascribed to it measured properties such as total energy E, as well as spin parameters / and Mj. However its actual definition is fraught with danger (particle/wave conundrum, and its sub-structure mystery), and the concept of its exact size is nebulous. Its electrical charge too does not bear too close a scrutiny, because of its potential sub-structure composed of other smaller particles. It seems clear that all the particles in our Universe interact, at some range, to some extent. 

Some older literature (especially for nuclides other than hydrogen) uses a definition of 8 in which vs and nR are reversed, so that the 8 scale is reversed in sign. Also, some early NMR chemical shifts are reported on the r scale in which r = 10 — 8. These arcane points are mentioned here only to clarify statements in older literature we shall adhere to the definition and conditions of Eq. 4.5. 

This scale is based on the nuclide mass of = 12 by definition, of the most stable or most common isotope is given in brackets. 

When a target nucleus is bombarded with a stream of particles x, there is a definite probability measured by the capture cross-section a of producing a new compound nucleus which rapidly rearranges to give a new nuclide... 

The half-life (t,/2) of a radioactive sample is defined as the time required for the number of nuclides to reach half of the original value (N0/2). We can use this definition in connection with the integrated first-order rate law (see Section 15.4) to produce the following expression for f1/2 ... 

Radioactive contamination Contamination with radioactive matter Radioactive decay Change of unstable atomic nuclei into other stable or unstable nuclei, associated with emission of nuclear radiation Radioactive equilibria Definite ratios between the activities of mother and daughter nuclides, given by their decay constants... 

As mentioned above, it is very useful to split the abundance distribution of the nuclides heavier than iron into three separate distributions giving the image of the SoS content of the p-, s- and r-nuclides. A rough representation of this splitting is displayed in Fig. 12. In its details, the procedure of decomposition is not as obvious as it might be thought from the very definition of the different types of nuclides, and is to some extent dependent on the models for the synthesis of the heavy nuclides. These models predict in particular that the stable nuclides located on the neutron-rich (deficient) side of the valley of nuclear stability are produced, to a first good approximation, only by the r-(p-)process. These stable nuclides are naturally called r-only and p-only nuclides, and their abundances are deduced directly from the SoS abundances. The situation is more intricate for the nuclides situated at the bottom of the valley of nuclear stability. Some of them are produced solely by the s-process,... 

I.U.B. definitions were indicated. Objections were made that the minute is not an S.I. unit. It was proposed to define enzyme activity by a catalytic amount (katal) of a system that catalyzes exactly as many cycles per second of a reaction scheme as there are atoms in 0.012 kg of the pure nuclide 12C. This point of view was adopted and recommended by the commission of Biochemical Nomenclature of I.U.B. in 1972, as appearing in Nomenclature and Classification of Enzymes, together with their units and symbols (revision and extension of recommendations of 1962 and 1964, Elsevier, Amsterdam, 1972). The katal was proposed as a unit of enzymic activity to be used instead of the earlier unit, and this recommendation was approved by the general assembly of the I.U.B. Congress at Stockholm, July 1973. 

Each nucleus is characterized by a definite atomic number Z and mass number A for clarity, we use the symbol M to denote the atomic mass in kinematic equations. The atomic number Z is the number of protons, and hence the number of electrons, in the neutral atom it reflects the atomic properties of the atom. The mass number gives the number of nucleons (protons and neutrons) isotopes are nuclei (often called nuclides) with the same Z and different A. The current practice is to represent each nucleus by the chemical name with the mass number as a superscript, e.g., 12C. The chemical atomic weight (or atomic mass) of elements as listed in the periodic table gives the average mass, i.e., the average of the stable isotopes weighted by their abundance. Carbon, for example, has an atomic weight of 12.011, which reflects the 1.1% abundance of 13C. 

The elements beyond the actinides in the Periodic Table can be termed the transactinides. These begin with the element having atomic number 104 and extend, in principle, indefinitely. Although only six such elements, numbers 104—109, were definitely known in 1991, there are good prospects for the discovery of a number of additional elements just beyond number 109 or in the region of larger atomic numbers. They are synthesized by the bombardment of heavy nuclides with heavy ions. 

A neutral atom consists of a small, dense central nucleus, about 10 cm in diameter, surrounded by a diffuse cloud of electrons whose outside diameter is around 10" cm. The nucleus contains most of the mass of the atom and carries a positive electric charge that equals a whole number times the electronic charge, 1.602101 X 10" C. This whole number is called the atomic number Z of the atom. It is identical with the serial number of the element in the periodic table. Each nucleus is made up of Z protons and a definite number N of neutrons. The total number of particles in the nucleus, N- Z, is called the mass number and is denoted by A. The mass number turns out to be the whole number nearest to the atomic weight of the nuclide. 

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. 

To perpetuate the name of Curie, the quantity of emanation in equilibrium with one gn.m of radium was termed a curie. This is an inconveniently large amount and the milli-micro curie is frequently used as a practical unit. It is the quantity of emanation in equilibrium with one millionth of a milligram of radium. Since one-fiftieth of this can be detected with a sensitive electroscope, this method of detecting the presence of radio-elements is extraordinarily sensitive — more so even than the spectroscope. The above definition of the curie has now been superseded. In July 1950 the Joint Commission on Standards, Units and Constants of Radioactivity defined the curie as the quantity of any radioactive nuclide in which the number of disintegrations per second is 3-700 X io10. 

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