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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


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.


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 2S1/2 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 2P3/2 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 2P3/2, 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.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:(Physics and Mathematics)
Degree Grantor:California Institute of Technology
Division:Physics, Mathematics and Astronomy
Major Option:Physics
Minor Option:Mathematics
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Lauritsen, Charles Christian
Thesis Committee:
  • Unknown, Unknown
Defense Date:1 January 1951
Funding AgencyGrant Number
Atomic Energy CommissionUNSPECIFIED
National Research CouncilUNSPECIFIED
Office of Naval ResearchUNSPECIFIED
Record Number:CaltechTHESIS:10042017-134730748
Persistent URL:
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:10485
Deposited By: Benjamin Perez
Deposited On:06 Oct 2017 22:21
Last Modified:04 May 2023 21:28

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