Deviations from Rutherford scattering in sub-Coulomb heavy-ion elastic scattering

Thesis/Dissertation · Tue Jan 01 04:00:00 EST 1980

OSTI ID:6238189

Lynch, W G

Both theoretical and experimental investigations have been carried out to look for small effects which can cause the differential cross-section of sub-Coulbom heavy ion elastic scattering to differ from the Rutherford cross-section. The present work focused on the elastic scattering of p-shell projectiles, specifically /sup 12/C, /sup 14/N, /sup 15/N, and /sup 16/O, from the doubly magic target nucleus /sup 208/Pb at laboratory bombarding energies ranging from 10 MeV to the Coulomb barrier (which occurs for example at E/sub lab/ approx. 44 meV for /sup 12/C, approx. MeV for /sup 16/O). For these systems, parameter free theoretical calculations which are an integral part of this disseration predicted that these sub-Coulomb data would be sensitive to four major effects: atomic screening, electron-positron vacuum polarization, nuclear polarization (virtual excitation of the giant dipole resonance), and a relativistic effect arising from the use of a relativistic wave equation in place of the Schroedinger equation. These same theoretical calculations indicated that the presence of these effects could be experimentally tested by measuring the energy dependence of the elastic scattering angular distributions. The experimental data were taken with fixed angle excitation functions instead of the more customary fixed energy angular distributions. Care was taken so that the experimental data which consisted of unnormalized measurements of the ratio R/sub b/f/(theta/sub i/)..cap alpha.. sigma(theta/sub i/)/sigma(30/sup 0/) at theta/sub i/ = 145/sup 0/, 150/sup 0/, 160/sup 0/, 170/sup 0/ could be taken with better than 1% accuracy. For pure Rutherford scattering, these ratios should be energy independent. Instead, all of the data consistently show the same projectile independent trend where the Ratio R/sub b/f/(theta/sub i/) steadily decreases with increasing beam energy with a total change in R/sub b/f/ greater than 1% as E/sub lab/ varies from 10 MeV to the Coulomb barrier.

• Research Organization: Washington Univ., Seattle (USA)
• OSTI ID: 6238189
• Country of Publication: United States
• Language: English

Related Subjects

640304* -- Atomic
Molecular & Chemical Physics-- Collision Phenomena
74 ATOMIC AND MOLECULAR PHYSICS
ANGULAR DISTRIBUTION
BASIC INTERACTIONS
CARBON 12 REACTIONS
CHARGED PARTICLES
CHARGED-PARTICLE REACTIONS
COULOMB FIELD
COULOMB SCATTERING
CROSS SECTIONS
DATA
DIFFERENTIAL CROSS SECTIONS
DISTRIBUTION
ELASTIC SCATTERING
ELECTRIC FIELDS
ELECTROMAGNETIC INTERACTIONS
ELECTRONIC STRUCTURE
ENERGY DEPENDENCE
ENERGY RANGE
EXCITATION FUNCTIONS
EXPERIMENTAL DATA
FUNCTIONS
HEAVY ION REACTIONS
HEAVY IONS
INFORMATION
INTERACTIONS
IONS
LEAD 208 TARGET
MEV RANGE
MEV RANGE 10-100
NITROGEN 14 REACTIONS
NITROGEN 15 REACTIONS
NUCLEAR REACTIONS
NUMERICAL DATA
OXYGEN 16 REACTIONS
RUTHERFORD SCATTERING
SCATTERING
TARGETS
THEORETICAL DATA
VACUUM POLARIZATION