Doorway States and Intermediate Structure Phenomena

T h e p h e n o m e n o n of the distribution o f a d o o r w a y state over m a n y c o m p l i c a t e d c o m p o u n d nuclear states, i. e . the f o r m a t i o n and properties of a so-cal led micro-giant resonance, are investigated analyt ical ly and n u m e r i c a l l y b y m e a n s of a s i m p l e m o d e l . T h e distribution of the poles in the c o m p l e x p l a n e and the distribution of the residues of the S -matr ix are obtained numerica l ly and used to calculate the average cross-section. I t is shown that the LANE-THOMAS-WIGNER theory applies , e x c e p t for a p o s s i b l e correction to the shape of the resonance occuring in the cross-section averaged over the energy . This shape n e e d not b e descr ibable b y a LoRENTzian. Estimates of the " s p r e a d i n g w i d t h " W a n d the " t o t a l w i d t h " J f 0 a r e g iven f o r particular c a s e s . I t i s noteworthy that the relat ionship JF0 = J F j T need not b e correct even as an order -o f -magnitude est imate , where r is the decay width of the d o o r w a y state.