THRESHOLD EFFECTS IN NEUTRON ELASTIC SCATTERING

Journal Article · Thu Aug 15 04:00:00 EDT 1963 · Physical Review (U.S.) Superseded in part by Phys. Rev. A, Phys. Rev. B: Solid State, Phys. Rev. C, and Phys. Rev. D

DOI:https://doi.org/10.1103/PhysRev.131.1644· OSTI ID:4669253

Wells, J T; Tucker, A B; Meyerhof, W E

In an attempt to observe the Wigner-cusp phenomenon in neutron elastic scattering near inelastic thresholds, the differential elastic and total cross sections of Li, Fe, Zr, Ba, and Ce near the threshold energy for exciting the firstexcited stutes of the dominant isotopes of these elements were measured. The energy region investigated extended approximately 300 kev on either side of threshold. Successful analysis of observed cusp phenomena can provide information on the spin and parity of excited stutes. In addition, the presence or absence of below-threshold effects in regions of neutron energy and atomic number where energy-averaged'' Wigner-cusp theory applies in principle can give an indication of the interaction mechanism, i.e., direct interaction or compound nucleus formation. The theory of Wigner cusps and energy-averaged'' Wigner cusps is supplemented in the present work by a consideration of slightiy more general angular-momentum situations and by explicit cusp expressions for differential-elastic cross sections. Cusp predictions are given in terms of the coefficients for expansion of the cross sections into a series of Legendre polynomials. This form facilitates comparison of theory and experiment. Unusual features were observed at the inelastic thresholds in the elastic and total cross sections of Li and Fe. Here one expects to notice a below, as well as above, threshold effect characteristic of Wigner cusps. In these cases, however, the interpretation of the experimental results is not unambigaous -in Li because the predicted cusp effect is too small to be observable in the present experiment and in Fe because the resonance structure of the cross sections overshadows the expected cusp effect. A drop, commencing at inelastic thresholds, is observed in the elastic cross sections of Ce, Ba, and Zr. Analysis of this effect in terms of the theory of energy-averaged'' Wigner-cusps yields good agreement between theory and experiment. (auth)

• Research Organization: Stanford Univ., Calif.
• NSA Number: NSA-17-031514
• OSTI ID: 4669253
• Journal Information: Physical Review (U.S.) Superseded in part by Phys. Rev. A, Phys. Rev. B: Solid State, Phys. Rev. C, and Phys. Rev. D, Journal Name: Physical Review (U.S.) Superseded in part by Phys. Rev. A, Phys. Rev. B: Solid State, Phys. Rev. C, and Phys. Rev. D Vol. Vol: 131; ISSN PHRVA
• Country of Publication: Country unknown/Code not available
• Language: English

Related Subjects

ANGULAR MOMENTUM
ATOMS
BARIUM
CERIUM
COMPOUND NUCLEI
CROSS SECTIONS
DIRECT REACTIONS
ELECTRIC CHARGES
ENERGY
ENERGY LEVELS
EXCITATION
INTERACTIONS
IRON
ISOTOPES
LEGENDRE FUNCTIONS
LEGENDRE POLYNOMIALS
LITHIUM
MATHEMATICS
MEASURED VALUES
MOMENTUM
NEUTRONS
NUCLEAR REACTIONS
NUCLEI
PARITY
PHYSICS
RESONANCE
SCATTERING
SPIN
WIGNER SCATTERING
ZIRCONIUM