STATISTICAL REACTIONS WITH MEMORY AND THERMALIZED-NONEQUILIBRATED NUCLEAR-STATES

Starting from the Feshbach S-matrix pole expansion we modify the stand ard statistical model for compound reactions by introducing correlatio ns between fluctuating S-matrix elements with different J (total spin) and pi (parity) values. The S-matrix (J, pi)-correlations are obtaine d at the expense of introducing infinitesimally small entrance-exit ch annel off-diagonal (J, pi)-correlations between the random variables o f the statistical model. Although later on these correlations are swit ched off by means of a properly applied limiting procedure, the S-matr ix (J; pi)-correlations do not vanish and can be strong. The physical origin of the S-matrix (J, pi)-correlations resembles the effect of sp ontaneous symmetry breaking while S-matrix (J, pi)-decoherence is due to quantum chaos. Novel reaction mechanism results in the excitation o f peculiar nuclear states: The intermediate system is thermalized so t hat the shape of the spectrum is angle-independent and Maxwellian with angle-independent slope, yet the intermediate nucleus is not equilibr ated since the angular distribution is forward-peaked, i.e., memory of the direction of the initial beam is not lost. The existence of therm alized-nonequilibrated nuclear states is supported by data on the 50-1 00% forward peaking of neutrons in the typically evaporation (1-3.5 Me V) part of the spectrum observed in the Nb-93(n, n') scattering with E -n = 7 MeV.