Thermal-neutron capture by {sup 14}N

Journal Article · Tue Jul 01 04:00:00 EDT 1997 · Physical Review, C

DOI:https://doi.org/10.1103/PhysRevC.56.118· OSTI ID:549760

Jurney, E T; Starner, J W; Lynn, J E ^[1]; Raman, S ^[2]

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1. Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)
2. Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831 (United States)

The energies and intensities of 58 {gamma} rays emitted in thermal-neutron capture by nitrogen (99.63{percent} {sup 14}N) have been measured accurately. A major reason was to establish this reaction as a standard for similar measurements on other nuclides. These {gamma} rays have been placed between 19 known levels (including the ground state and the capturing state) in {sup 15}N. The primary {gamma} rays of both electric dipole (E1) and magnetic dipole (M1) types have been analyzed with existing theories of slow-neutron capture. Unlike many other light nuclides, the cross sections for E1 transitions in {sup 15}N differ drastically from the calculations of pure direct-capture theory. The role of the resonance-capture contribution from the proton-unbound, neutron-bound level at 29{plus_minus}2keV below the neutron separation energy was considered. Some of the properties of this level are quite well known from the {sup 14}C(p,{gamma}) reaction, and others can be derived from an R-matrix analysis of the total cross section as a function of neutron energy. The thermal-neutron capture {gamma}-ray spectrum is different from the proton-capture {gamma}-ray spectrum, but if proper account is taken of the interference among the compound-nuclear processes, the valence-neutron mechanism, and potential capture, the data can be satisfactorily explained. In the thermal-neutron reaction, compound-nuclear E1 and direct-capture E1 contributions are of comparable magnitude. Valence-neutron capture forms a significant component of capture by the neutron-bound level at {minus}29keV. Largely destructive interference between compound-nuclear and valence processes in a few transitions in thermal-neutron capture gives rise to a much smaller total cross section than would be obtained from the compound-nuclear process alone. The M1 transitions also show some evidence of a direct process but not a dominant one. (Abstract Truncated)

• Research Organization: Oak Ridge National Laboratory
• DOE Contract Number: AC05-96OR22464; W-7405-ENG-36
• OSTI ID: 549760
• Journal Information: Physical Review, C, Journal Name: Physical Review, C Journal Issue: 1 Vol. 56; ISSN PRVCAN; ISSN 0556-2813
• Country of Publication: United States
• Language: English

Related Subjects

66 PHYSICS
CAPTURE
COMPOUND NUCLEI
E1-TRANSITIONS
ENERGY
GAMMA RADIATION
GROUND STATES
NITROGEN 14
NITROGEN 15
R MATRIX
THERMAL NEUTRONS