Fine Structure Discussion of Parity-nonconserving Neutron Scattering at Epithermal Energies

The large magnitude and the sign correlation effect in the parity non-conserving resonant scattering of epithermal neutrons from Th is discussed in terms of a non-collective 2p− 1h local doorway model. General conclusions are drawn as to the probability of finding large parity violation effects in other regions of the periodic table. PACS numbers: 25.40.Ny, 11.30.Er, 24.10.Ht, 24.80.Dc CTP# 2296 September 08, 1994 * This work is supported in part by funds provided by the U. S. Department of Energy (D.O.E.) under cooperative agreement #DE-FC02-94ER40818. † Permanent address: Instituto de F́ısica, Universidade de São Paulo, C. P. 20516, São Paulo S. P. Brazil. Supported partly by FAPESP (Brazil) ‡ Supported by Conselho de Desenvolvimento Cient́ıfico e Tecnológico(CNPq) 1 The discovery of sign correlation in parity non-conserving (PNC) epithermal neutroninduced compound-nucleus reactions involving the heavy nucleus Th has prompted intensive theoretical discussion concerning their origin. The great interest in the TRIPLE data [1]stems from the fact that the statistical theory (ST) of these reactions, although it predicts the possibility of large PNC at individual resonances as the data also show, rules out any sign correlations in the longitudinal asymmetry, contrary to what the data show. The quantity usually analysed is the longitudinal asymmetry. At a given p1/2 resonance in the compound nucleus P = σ (+) R − σ (−) R σ (+) R + σ (−) R (1) where σ (±) R is the resonance neutron cross-section for ± helicities at a given p1/2 resonance. We now use the usual formula for the total cross-section σ (±) T = 4π k Imf (0) = σ (±) 0 + σ (±) R , (2) with f (0) = f 0 − 1 2k ∑