STATISTICAL SIGNIFICANCE OF SPREADING WIDTHS FOR DOORWAY STATES

The strength function constructed as the Lorentz-weighted average of the reduced widths of the Wigner-Eisenbud R matrix (or of a reactance K matrix) is a continuous and well-defined function of energy for a fragmented doorway state (isobaric analog resonance, fission isomer, etc.) in both weak and strong coupling. If the half-width I of the Lorentz weighting function is chosen appropriately, this strength function itself approximates a Lorentzian whose width is the spreading width I+ of Feshbach, Kerman, and Lemmer. An ensemble of 400 doorway systems characterized by coupling strengths ranging from strong to weak is used to study properties of I+ and to determine the accuracy with which it can be determined for a particular doorway by a least-squares fit to the strength function. The results of this numerical study show that (1) I+ is a characteristic of each doorway state system, and that (2) its value can be determined from experimentally measured resonance energies and widths with an uncertainty which is less than the fluctuations in its value from one system to another and which decreases as the coupling strength decreases. NUCLEAR REACTIONS spreading of doorway states, fine structure, isobaric analog states. © 1979 The American Physical Society.