Nuclides table

River runoff and i situ production are the major sources of U-Th series nuclides (Table 1) to the oceans. The concentrations of the various U-Th series nuclides in rivers vary considerably and depend upon several factors prime among them being their chemical reactivity [13], the chemistry of river water, and the nature of the river bed. 

The radioactive emission rate is determined by the relative stability of the nuclide. One valid measure of the stability of the nuclide is its half-life. The idea is that the decay rate obeys Poisson6 statistics, and the number of radioactive nuclei at time t is n(t) = n(0) exp( t/t1/2), where fi/2 is the half-life. Appendix Table A is a complete list of all known nuclides. Table 10.1 lists some nuclides, their decay products, their half-life, and their uses. 

The final members of the decay series are stable nuclides ° Pb at the end of the thorium family, Pb at the end of the uranium-radium family, Pb at the end of the actinium family, and Bi at the end of the neptunium family. In all four decay series one or more branchings are observed. For instance, Bi decays with a certain probabihty by emission of an a particle into Tl, and with another probability by emission of an electron into Po. os-pj decays by emission of an electron into Pb, and Po by emission of an a particle into the same nuclide (Table 4.1), thus closing the branching. In both branches the sequence of decay alternates either a decay is followed by P decay or p decay is followed by a decay. 

The classic idea of a cosmic-ray exposure (CRE) age for a meteorite is based on a simple but useful picture of meteorite evolution, the one-stage irradiation model. The precursor rock starts out on a parent body, buried under a mantle of material many meters thick that screens out cosmic rays. At a time fj, a collision excavates a precursor rock—a meteoroid. The newly liberated meteoroid, now fully exposed to cosmic rays, orbits the Sun until a time ff, when it strikes the Earth, where the overlying blanket of air (and possibly of water or ice) again shuts out almost all cosmic rays (cf. Masarik and Reedy, 1995). The quantity ff — h is called the CRE age, f. To obtain the CRE age of a meteorite, we measure the concentrations in it of one or more cosmogenic nuclides (Table 1), which are nuclides that cosmic rays produce by inducing nuclear reactions. Many shorter-lived radionuclides excluded from Table 1 such as Na (ff/2 = 2.6 yr) and °Co ty = 5.27 yr) can also furnish valuable information, but can be measured only in meteorites that feu within the last few half-Uves of those nucUdes (see, e.g., Leya et al. (2001) and references therein). 

The last matter to be dealt with before the spectrum is plotted is selecting an appropriate zero reference for the signals in the spectrum. This subject was mentioned briefly in Section 1-2, where we saw that reference materials have been agreed upon, for the most part, for each nuclide (Table 1-2) and assigned a relative frequency of zero. We also learned that the compound tetramethylsilane (TMS) serves as an internal zero reference for protons, carbon, and silicon. 

In thermal-neutron reactors has an important advantage over or Pu in that the number of neutrons produced per thermal neutron absorbed, tj, is higher for than for the other fissile nuclides. Table 6.1 compares the 2200 m/s cross sections and neutron yields in fission of these three nuclides. Thorium has not heretofore been extensively used in nuclear reactors because of the ready avaUabihty of the U in natural or slightly enriched uranium. As natural uranium becomes scarcer and the conservation of neutrons and fissile material becomes more important, it is anticipated that production of U from thorium will become of greater significance. 

A wide range of radioactive nuclides ( Table 59.4) may be employed for RTGs as power sources. According to the fabrication method, they may be divided into four groups (Radioizotopnye istochniki elektricheskoy energii 1978, Mashinostroyenie Entsiklopediya) ... 

Most standards for nuclear criticality safety deal with U and, to a lessw degree. and Pu. However, increasing production df other transuranium nuclides that can be made critical has necessitated consideration of the fis e properties. and critical masses of these special materials. A work group (Table I) was formed to draft a new standard that would be an extension of the standard for criticality safety in Operations outside of reactors (NI6.1-197S/ANS- -8.1). Subcritical mass limits for 14 new nuclides (Tables II and. Ill), were developed however, fire major application of thb hew standard is expected to be te setting operational liihits in facilities that handle six important nuclides, namely, Np, " u. Pu, "Aih, and n m. 

Fig. ilC.l. Nuclidic table representation of rare earths and interfering molecular ions for a cerium matrix. 

The activation production cycle requires only neutron irradiation without chemical separation. The target and the product are the same chemical element but have different nuclide compositions. The specific radioactivity of the product is a function of the nuclide composition of the target, the neutron flux environment, the irradiation time, and the half-life of the product nuclide, along with the nuclear cross sections of target and product nuclides (Table 31.8). 

TABLE 4.16 Table of Nuclides Explanation of Column Headings... 

Several portions of Section 4, Properties of Atoms, Radicals, and Bonds, have been significantly enlarged. For example, the entries under Ionization Energy of Molecular and Radical Species now number 740 and have an additional column with the enthalpy of formation of the ions. Likewise, the table on Electron Affinities of the Elements, Molecules, and Radicals now contains about 225 entries. The Table of Nuclides has material on additional radionuclides, their radiations, and the neutron capture cross sections. 

Table 2. Long-Lived Actinide Nuclides Suitable for Investigation...

Our present views on the electronic structure of atoms are based on a variety of experimental results and theoretical models which are fully discussed in many elementary texts. In summary, an atom comprises a central, massive, positively charged nucleus surrounded by a more tenuous envelope of negative electrons. The nucleus is composed of neutrons ( n) and protons ([p, i.e. H ) of approximately equal mass tightly bound by the force field of mesons. The number of protons (2) is called the atomic number and this, together with the number of neutrons (A ), gives the atomic mass number of the nuclide (A = N + Z). An element consists of atoms all of which have the same number of protons (2) and this number determines the position of the element in the periodic table (H. G. J. Moseley, 191.3). Isotopes of an element all have the same value of 2 but differ in the number of neutrons in their nuclei. The charge on the electron (e ) is equal in size but opposite in sign to that of the proton and the ratio of their masses is 1/1836.1527. 

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