I. Spectrometer Measurements of the Rates of Gamma Radiation and Internal Pair Formation from Some Nuclear Reactions in Light Nuclei. II. Theory of the Energy Levels of the Mirror Nuclei, C^(13) and N^(13)

I. SPECTROMETER MEASUREMENT OF THE RATES OF GAMMA-RADIATION AND INTERNAL PAIR FORMATION FROM SOME REACTIONS IN LIGHT NUCLEI ABSTRACT - PARTS I - III In part III the measurements with beta-ray spectrometer of the gamma-rays and internally-formed positrons from the reactions C 13 (dp)C 14 and C 13 (dn)N 14 are described; the energy levels of N 14 and C 14 are discussed. A measurement of the internally-formed positron spectra from the Be 9 + d reactions is described, and an attempt is made to determine the multipolarity of the 2.87- and 3.38-Mev transitions from the ratio of the rates of pair emission to gamma radiation; the results are in agreement with electric-dipole assignments to the transitions. Also described is the measurement of the internal conversion electrons associated with the 0.871-Mev radiation from the O 16 (dp)O 17 reaction; the result is shown to be consistent with an electric quadripole assignment to this transition. In Part II methods are developed for analyzing the date of Part III. These include the measurement of absolute gamma-ray intensities by Compton conversion of the radiation in thick foils and photoelectric conversion in thin foils. Methods for analyzing internal-pair spectra and internal conversion spectra are given and several problems discussed. Measurements of the internal conversion coefficients of the 0.713-Mev transition of B 10 and the 1.332-Mev transition of Ni 60 are described. Part I is concerned with the penetration of the secondary electrons through the converters in which they are produced. The effective stopping power of aluminum and beryllium are calculated for use in the Compton thick - converter method of measuring gamma-ray intensities developed in Part II. Also included is a discussion of the scattering of electrons in the converters. II. ENERGY LEVELS OF THE MIRROR NUCLEI, N 13 AND C 13 ABSTRACT PART IV The low energy levels ( 13 and C 13 , are studied on the assumption that rr and pp nuclear forces are equal. By means of dispersion theory it is shown that the first excited states of these nuclei are 2 S 1/2 and that the large displacement is due to their large reduced width and the difference in the extra-nuclear wave functions for the odd particle; the magnitude of the reduced widths suggests that a one-body type of interaction is involved between the odd particle and the C 12 core. In particular, a square-well type of model gives a satisfactory account of the level shift, reduced widths, and the low-energy (< 1 Mev) scattering of neutrons by carbon. The C 12 + n s-wave interaction is also studied by means of the effective range theory. Some evidence is given that the second excited state of N 13 is a doublet, one component of which appears at 3.68-Mev and the other at 3.90-Mev in C 13 , and the 3.68-Mev component is most likely 2 P 3/2 and the 3.90 2 d. The reduced width of the ground states of N 13 and C 13 , as calculated from the knowledge of the s-wave C 12 (p γ) and C 12 (n γ) cross sections, is about 1/10 of the value expected for a familiar one-body type of interactions, but it is nearly equal to the reduced width of the 3.52-Mev level of N 13 . This reduced width is used to calculate the ground-state level shift due to the difference in the extra-nuclear wave functions. The shift of the second pair of excited states, if they are 2 P 3/2 , can be about 1/3 accounted for as due to the difference of the extra-nuclear wave functions for the odd particle and about 1/3 as due to the difference in the electromagnetic spin-orbit interactions of the odd particle.