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Recent years have seen the accumulation of a considerable amount of new information, both experimental and theoretical, pertaining to the location and character of the excited states in the light nuclei. We have attempted in the following sections to summarize the pertinent facts appearing in the literature and to present this material in a systematic way. To a large extend the organization of the present article follows the pattern of the two previous papers on this subject.(1,2) The present article contains a summary of the most important information appearing in the earlier papers and is intended to supersede them entirely.

In most recoilless gamma-ray resonance experiments the magnetic-dipole and electric-quadrupole hyperfine interaction do not cause any shift of the center of gravity of the velocity spectrum. This is usually related to the fact that the trace of the hyperfine-interaction Hamiltonian is zero. Nevertheless a large shift can be caused under proper conditions by a magnetic hyperfine interaction in second order, the so-called "pseudoquadrupole" interaction.(1) This paper reports the first observation of the pseudoquadrupole shift of gamma lines.(2)

Calculations of many physical processes according to the SU(12) theories(1) can be facilitated by the use of appropriate subgroups of SU(12). Direct calculations are difficult because of the complexity of the group and the present lack of available Clebsch-Gordan coefficients. Tables of SU(6) Clebsch-Gordan coefficients do exist,(2) however, and have been used for calculations of non-relativistic processes. In this paper we present SU(6) subgroups which differ from the conventional SU(6) by the replacement of ordinary spin by different SU(2) subgroups of SU(12).

Spectra of stripped atoms, sodium to chlorine.—Grating spectrograms of order three to eight have been obtained of the hot-spark spectra of these elements, which have yielded more accurate values for the (3p2-3p1), (3s-3p2) and (3p1-3d) terms of AlIII, SiIV, PV and SVI, and have enabled the identification and determination within about 5 frequency units (1) of 18 series lines of PV, and thence of the 14 most important term values (3s to 6f′′), (2) of 11 series lines of SVI, and 10 corresponding term values (3s to 5f′), and (3) of the first doublet of the principal series of ClVII at 800.70 and 813.00 A. The position of this doublet was first predicted by use of the method developed in a previous paper(1), based on observed regularities in these spectra. Further evidence is presented for the fact that both the regular and the irregular doublet laws of x-ray spectra, hold also throughout the field of optics. A plot of sqrt[ν/R] for the stripped atom levels as a function of atomic number gives approximately straight lines (Moseley law), those for the 3s, 3p and 3d terms and for the 4s, 4p, 4d and 4f terms being approximately parallel (irregular doublet law). The doublet separations d1d2, however, do not fit well into the relativity doublet law, the ratio of observed to theoretical values decreasing from about .8 for SVI to less than .2 for SiIV, while AlIII and MgII are anomalous, d1 having a greater frequency than d2. The general similarity of the spectra of all these elements is strikingly shown in spectrograms on which appear the "D" doublet of Na and the corresponding "D" doublets of the stripped atoms of Mg, Al, Si, P, S, and Cl in the second, third, fourth, fifth, sixth and seventh ordelrs, respectively, all near 5600 A, that for Na being farthest from the mean position. The frequencies of all the known terms found for the stripped atoms of Na to S, are collected in a table. Ionization potentials of PV and SiVI, computed from the 3s levels of PV and SVI, come out 64.7 and 87.6 volts.

The invited speakers have done an excellent job of describing the various topics within the field of weak interactions. The contributed papers have presented many fascinating results. Furthermore, what is rare these days at a physics conference, there has been plenty of discussion, which has brought out, I think, every point that was overlooked in the speeches. Evidently, there is no need for a summary. A few words about what appear to me to be the principal questions that we would like to have answered in the future are given in the following.

Series spectra of three-valence-electron atoms of P, S and Cl.—By the methods of the preceding paper, 21 lines of PIII have been identified, 20 lines of SIV and 10 lines of ClV, including a pp′ group for each; also 10 term values of PIII have been determined and 10 term values of SIV, including the x level. Screening constants for one, two, and three valence electron systems are collected in a table for Na to Cl. The values increase regularly with the number of valence electrons and decrease with the atomic number, the difference decreasing as the atomic number increases.