Mirror nuclides

MIRROR NUCLIDES. Pairs uf nudities, having their numhers of protons and neutrons so related that each member of the pair would be transformed into the other hv exchanging all neutrons for protons and vice versa. 

Classification of p transmutations and selection rules are listed in Table 5.2. The lowest ft values are observed for nuclides that are transformed into a mirror... 

Figure 6-21 illustrates this procedure for an adamantane derivative. The H frequencies are on the vertical axis and the C frequencies are on the horizontal axis. The respective spectra are illustrated on the left and at the top. The 2D spectrum is composed only of cross peaks, each one relating a carbon to its directly bonded proton(s). There are no diagonal peaks (and no mirror symmetry associated with a diagonal), because two different nuclides are represented on the frequency dimensions. Quaternary carbons are invisible to the technique, as the fixed times A and A2 normally are set to values for one-bond couplings. This experiment often is a necessary component in the complete assignment of H and resonances. Its name, HETeronuclear chemical Shift CORrelation, usually is abbreviated as HETCOR, but other acronyms (e.g., HSC, for Heteronuclear Shift Correlation, and H, C-COSY, also are used. The method may be applied to protons coupled to many other nuclei, such as Si, and P, as well as C. 

It generally holds that the intensity of an HMBC cross peak drops off as the number of bonds separating the two coupled nuclides (normally H and C) increases because cross peak intensity roughly mirrors the magnitude of the J-coupling between the two species. 

A strong overlap of initial and final wave functions is expected for mirror nuclei, in which the mass numbers are identical, but the atomic number in one nucleus is equal to the neutron number of the other. The large overlap integral results in a very low fi value (superallowed transitions). Most of the known P emitters decay by allowed or superallowed transitions. Among the light nuclides there are many mirror pairs. 

A Co emission study, at the first glance, is just a simple mirror image of an Fe transmission study only the roles of the source and absorber are exchanged. However, it would be true only if the material investigated contained iron, and the dopant material would be Fe instead of its mother nuclide Co. Thus, the following important differences may be taken into account when emission results are interpreted or compared with transmission studies ... 

The cardinal points of intersection of the hemlines of Fig. 7 at Z/N = 1.04 are arranged symmetrically about Z = 51. On identification of the points Z = 0 and 102, a closed function is generated. Operating with the same element of mirror symmetry on the hemlines, two sets, characteristic of both nuclides and antinuclides, are generated as shown in Fig. 8. 

---