Nuclei 6-strength functions

Examples of large-basis shell-model calculations of Gamow-Teller 6-decay properties of specific interest in the astrophysical s-and r- processes are presented. Numerical results are given for i) the GT-matrix elements for the excited state decays of the unstable s-process nucleus "Tc and ii) the GT-strength function for the neutron-rich nucleus 130Cd, which lies on the r-process path. The results are discussed in conjunction with the astrophysics problems. 

We discuss some features of a model for calculation of p-strength functions, in particular some recent improvements. An essential feature of the model is that it takes the microscopic structure of the nucleus into account. The initial version of the model used Nilsson model wave functions as the starting point for determining the wave functions of the mother and daughter nuclei, and added a pairing interaction treated in the BCS approximation and a residual GT interaction treated in the RPA-approximation. We have developed a version of the code that uses Woods-Saxon wave functions as input. We have also improved the treatment of the odd-A Av=0 transitions, so that the singularities that occured in the old theory are now avoided. 

In the black-nucleus statistical model, Sp — lO (see, e.g., ref. [2]). However, the single particle mode does not dissipate completely and the strength function can be produced as [82]... 

Nuclear magnetic resonance (nmr) requires an atomic nuclei that can absorb a radio-frequency signal impinging it in a strong magnetic field to give a spectmm. The field strength at which the nucleus absorbs is a function of both the nucleus and its immediate electronic environment. The atoms normally used for nmr analysis are as follows (34) H, F, P, Si, and Of these, the most commonly used in polymer analyses are... 

Figure 5.9 Relative energy of both spin states of an / = 1/2 nucleus as a function of the strength of the external magnetic field Bo. After Macomber [160]. Reprinted from R.S. Macomber, A Complete Introduction to Modern NMR Spectroscopy, John Wiley Sons, Inc., New York, NY, Copyright (1998, John Wiley Sons, Inc.). This material is used by permission of John Wiley Sons, Inc.

Chemical shift (8) A dimensionless quantity defined as 8 = (Vsample - vreference)/v0 X 106, where vsample is the resonance frequency of the sample, vreference is the resonance frequency of the reference, tetramethylsilane (TMS defined as zero), and v0 is the observing frequency (e.g., 300 or 600 MHz). The unit for the 8 scale is ppm (parts per million) and is independent of the strength of the applied magnetic field. Exact resonance frequency of a nucleus is a function of the environment (chemical/magnetic) of the observed nuclei. 

However, it is possible to probe such a relativistic dynamics with a second field with a lower frequency, so that multiphoton absorption, leading to ATI, can take place. In order to ionize such a stabilized atom with a significant, probability, the second field must force the electron wave function to explore again the vicinity of the nucleus to be able to absorb energy (i.e. photons). This can he achieved by chosing parallel polarizations and field strength intensities and frequencies such that the characteristic excursion lengths [Pg.114]

The strength of this attraction is based on two factors the distance from the nucleus to the outermost electrons, and the valence electron pattern. The distance factor is a function of the fact that the closer the nucleus is to the outer electrons, the greater the power of the nucleus in pulling in other electrons. This is similar to the observation that a magnet works best when close to an object. As the valence electron pattern approaches the noble gas valence electron pattern, the more effective the element is at attracting electrons. Noble gases have virtually no electronegativity, as they rarely react. 

Figure 2.5. Relative energy of both spin states of an / = nucleus as a function of the strength of the external magnetic field Bq.

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