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, C¹³ and N¹³

Citation

Thomas, Robert G. (1951) 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, C¹³ and N¹³. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/6KAK-R867. https://resolver.caltech.edu/CaltechTHESIS:10042017-134730748

Abstract

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 C¹³(dp)C¹⁴ and C¹³(dn)N¹⁴ are described; the energy levels of N¹⁴ and C¹⁴ are discussed. A measurement of the internally-formed positron spectra from the Be⁹ + 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 O¹⁶(dp)O¹⁷ 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 B¹⁰ and the 1.332-Mev transition of Ni⁶⁰ 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, N¹³ and C¹³

Abstract - part IV

The low energy levels (< 6 Mev) of the mirror nuclei, N¹³ and C¹³, 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 ²S_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 C¹² 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 C¹² + n s-wave interaction is also studied by means of the effective range theory. Some evidence is given that the second excited state of N¹³ is a doublet, one component of which appears at 3.68-Mev and the other at 3.90-Mev in C¹³, and the 3.68-Mev component is most likely ²P_3/2 and the 3.90 ²d. The reduced width of the ground states of N¹³ and C¹³, as calculated from the knowledge of the s-wave C¹²(p γ) and C¹²(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 N¹³. 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 ²P_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.

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