Discontinuities in the level spacings observed with 52Cr + n resonances

The total neutron cross section of 52Cr has been measured using the neutron time-of-flight technique at the pulsed electron linear accelerator (GELINA) of CBNM, Geel. Data analysis has been performed over the neutron energy range 1 keV to 1 MeV with an R-matrix multilevel multichannel code to determine the resonance parameters. The following non-statistical effects in the level spacings are indicated in the resonance parameter set: two gaps are observed in the s-wave level distribution, where at least two resonances for each gap are missing; a strong discontinuity in the level spacing is observed for p-wave resonances whereby three energy ranges, up to 600 keV, with different level spacings may be distinguished. This energy dependent behaviour of the p-wave level density causes parity dependence of nuclear states in the range (200-600) keV. The p-wave strength function is constant except for the strong local enhancement of the level spacing at 250 keV. These deviations in the resonance parameters from statistical behaviour may be explained by doorway structures with a small spreading width, as has been observed for 28Si and 32S which, like 52Cr, have a multiple of four nucleons in the target nucleus. (author)