Structure of 19O from measurement and R-matrix analysis of sigma(theta) for 18O(n,n)18O and 18O(n,n')18Osup(*) (1.98 MeV)

Differential cross sections for neutrons elastically scattered from 18O and inelastically scattered to the first excited state 18Osup(*) (1.98 MeV) have been measured at forty-two incident energies for 5.0 < Esub(n) < 7.5 MeV corresponding to excitation energies in 19O of 8.7 to 11.1 MeV. The cross sections were measured at eleven laboratory angles per energy from 200 to 1600 and show considerable resonance structure. These new elastic and inelastic 1.98 MeV level data have been analyzed together with previously published cross sections for 0 < Esub(n) < 2.5 MeV using a multilevel-multichannel R-matrix program to determine J, π, Esub(lambda) and γsub(lambdac) for states in 19O. The new assignments are compared to previous work where possible. Several previous assignments for resonances in the 0 < Esub(n) < 2.5 MeV region were verified, and disagreements over the Jsup(π) assignments for several levels in this region have been resolved. A total of fourteen new Jsup(π) assignments were made in the 5 < Esub(n) < 7.5 MeV region. An attempt was made to identify T=3/2 analog states in 19F for the newly assigned levels in 19O. On the basis of spin, parity, excitation energy and a comparison of reduced neutron widths in 19O with reduced proton widths in 19F, six previously-identified T=3/2 analogs were verified and eight new T=3/2 analogs were tentatively assigned. Comparisons with existing theoretical work are discussed. (orig.)