Nuclear systematics

A happy consequence of nuclear systematics is that element 104 is in Group 4, element 105 is in Group 5, etc. This mnemonic holds to the end of the transition series at element 112 and presumably beyond it can be compared with the similar relation between the group numbers of the post-transition main-group elements (13-18) and the group numbers of the preceding transition elements (3-8). 

Since there is a lack of experimental data on neutron cross sections for Cm-241. fast-neutron cross sections were generated by means of nuclear systematics and nuclear models. The NK.VRREX and 2-PLUS" codes were used to generate the neutron cross sections that were then used to calculate the critical mass of Cm-244 as a function of density. Fig. 1. 

The virtues of collinear-beam spectroscopy for nuclear systematics are best demonstrated by the chart of nuclides (Figure 9) on which the investigated longer chains of unstable isotopes are marked by solid frames. The majority of the results were obtained from collinear-beam measurements, while the rest is shared by a number of more specialized techniques (see, e.g.. Refs. 127-128). In a few cases the measurements cover nearly all known isotopes, and examples of nuclear physics results will be given in Section 5.4. 

In spite of worldly distractions, Glenn Seaborg has never wavered in his life-long commitment to science. He continues his research into the chemistry and nuclear systematics of the actinide elements. Recently, he has focused his attention on the possible existence of still another family of superheavy elements at the end of the Periodic Table, and the development of new methods for the synthesis of superheavy elements. The dedication of these volumes to Glenn Seaborg is not only a testimonial to his scientific achievements, it is also an appreciation of the example that he continues to set. 

Viola Jr, V.E., Seaborg, G.T. Nuclear systematics of the heavy elements—II lifetimes for alpha, beta and spontaneous fission decay. J. Inorg. Nucl. Chem. 28, 741-761 (1966)... 

The paper presents the results from systematic comparisons of contrast and resolution obtained with different types of radiation sources on steel thicknesses from 5 to 40 mm. These results have been taken into account with the definitions of the European standard for radiographic inspection of weldments (EN 1435) that is approved since 1997. Conclusions from practical investigations on pipe line sites, in petrochcemical plants and in nuclear power stations will be discussed as well. Furthermore, the presentation will stipulate a variety of advantages obtained from the new source in terras of coUimation and radiation protection. 

Election nuclear dynamics theory is a direct nonadiababc dynamics approach to molecular processes and uses an electi onic basis of atomic orbitals attached to dynamical centers, whose positions and momenta are dynamical variables. Although computationally intensive, this approach is general and has a systematic hierarchy of approximations when applied in an ab initio fashion. It can also be applied with semiempirical treatment of electronic degrees of freedom [4]. It is important to recognize that the reactants in this approach are not forced to follow a certain reaction path but for a given set of initial conditions the entire system evolves in time in a completely dynamical manner dictated by the inteiparbcle interactions. 

Whatever the derivative considered, the nuclear magnetic resonance spectra of thiazoles are remarkably simple and apparently univoque. The first proton NMR spectrum of thiazole was described by Bak et al. (171). It was followed by a series of works establishing a systematic description... 

Fragola, J. R. et al., 1983, A Systematic Approach to Human Error Categorization in Nuclear Power Plant Tasks ANS Trans. 44 p 176, June. 

The confidence limits of a measurement are the limits between which the measurement error is with a probability P. The probability P is the confidence level and a = 1 - P is the risk level related to the confidence limits. The confidence level is chosen according to the application. A normal value in ventilation would be P = 95%, which means that there is a risk of a = 5 /o for the measurement error to be larger than the confidence limits. In applications such as nuclear power plants, where security is of prime importance, the risk level selected should be much lower. The confidence limits contain the random errors plus the re.sidual of the systematic error after calibration, but not the actual systematic errors, which are assumed to have been eliminated. 

Embrey, D. E (1986). SHERPA A Systematic Human Error Reliability Prediction Approach. Proceedings of the American Nuclear Society International Topical Meeting on Advances in Human Factors in Nuclear Power Systems. 

A further group of elements, the transuranium elements, has been synthesized by artificial nuclear reactions in the period from 1940 onwards their relation to the periodic table is discussed fully in Chapter 31 and need not be repeated here. Perhaps even more striking today are the predictions, as yet unverified, for the properties of the currently non-existent superheavy elements.Elements up to lawrencium (Z = 103) are actinides (5f) and the 6d transition series starts with element 104. So far only elements 104-112 have been synthesized, ) and, because there is as yet no agreement on trivial names for some of these elements (see pp. 1280-1), they are here referred to by their atomic numbers. A systematic naming scheme was approved by lUPAC in 1977 but is not widely used by researchers in the field. It involves the use of three-letter symbols derived directly from the atomic number by using the... 

Probably the most important development of the past decade was the introduction by Brown and co-workers of a set of substituent constants,ct+, derived from the solvolysis of cumyl chlorides and presumably applicable to reaction series in which a delocalization of a positive charge from the reaction site into the aromatic nucleus is important in the transition state or, in other words, where the importance of resonance structures placing a positive charge on the substituent - -M effect) changes substantially between the initial and transition (or final) states. These ct+-values have found wide application, not only in the particular side-chain reactions for which they were designed, but equally in electrophilic nuclear substitution reactions. Although such a scale was first proposed by Pearson et al. under the label of and by Deno et Brown s systematic work made the scale definitive. 

In this review recent theoretical developments which enable quantitative measures of molecular orientation in polymers to be obtained from infra-red and Raman spectroscopy and nuclear magnetic resonance have been discussed in some detail. Although this is clearly a subject of some complexity, it has been possible to show that the systematic application of these techniques to polyethylene terephthalate and polytetramethylene terephthalate can provide unique information of considerable value. This information can be used on the one hand to gain an understanding of the mechanisms of deformation, and on the other to provide a structural understanding of physical properties, especially mechanical properties. 

To properly describe electronic rearrangement and its dependence on both nuclear positions and velocities, it is necessary to develop a time-dependent theory of the electronic dynamics in molecular systems. A very useful approximation in this regard is the time-dependent Hartree-Fock approximation (34). Its combination with the eikonal treatment has been called the Eik/TDHF approximation, and has been implemented for ion-atom collisions.(21, 35-37) Approximations can be systematically developed from time-dependent variational principles.(38-41) These can be stated for wavefunctions and lead to differential equations for time-dependent parameters present in trial wavefunctions. 

The use of computer simulations to study internal motions and thermodynamic properties is receiving increased attention. One important use of the method is to provide a more fundamental understanding of the molecular information contained in various kinds of experiments on these complex systems. In the first part of this paper we review recent work in our laboratory concerned with the use of computer simulations for the interpretation of experimental probes of molecular structure and dynamics of proteins and nucleic acids. The interplay between computer simulations and three experimental techniques is emphasized (1) nuclear magnetic resonance relaxation spectroscopy, (2) refinement of macro-molecular x-ray structures, and (3) vibrational spectroscopy. The treatment of solvent effects in biopolymer simulations is a difficult problem. It is not possible to study systematically the effect of solvent conditions, e.g. added salt concentration, on biopolymer properties by means of simulations alone. In the last part of the paper we review a more analytical approach we have developed to study polyelectrolyte properties of solvated biopolymers. The results are compared with computer simulations. 

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