Direct measurement of natural line widths in delayed-neutron energy spectra

Delayed-neutron spectra of mass-separated fission products from the TRISTAN facility at Brookhaven are being investigated to develop systematics of neutron resonances in the 1 to 100 keV range in neutron-rich nuclides as a unique experimental basis for testing theoretical extrapolations of level parameters and neutron cross sections from stable to very unstable nuclides. Aims, methods, and early results have been described elsewhere. The time-of-flight system yields resolved peaks, >10 between 3 and 100 keV in Rb-95 and Rb-97. Natural line widths have been deduced to date for two Rb-95 peaks: 414 +- 33 eV for the 14.44 +- 0.09 keV resonance and 670 +- 270 eV for the 26.70 +- 0.13 keV resonance, found by fitting the experimental data to a Lorentzian convoluted with a calculated system response function. Similar analysis of further peaks and deduction of level densities and other parameters await additional data from newly improved apparatus and planned experimental checks of the resolution calculation by measuring the Br-87 spectrum and comparing it with known resonance parameters of the Kr-86 + n cross section. 5 refs