Neutron Total Cross Sections in the kev Region by Fast Time-of-Flight Measurements

A new method employing millimicrosecond time measurement has been used to study neutron total cross sections in the 2- to 30-kev energy range. The method has been applied to the nuclides Na²³, Al²⁷, P³¹, K³⁹, K⁴¹, Rb⁸⁵, Rb⁸⁷, Sr⁸⁶, Sr⁸⁸, Y⁸⁹, Bi²⁰⁹, and to natural Ti, Se, and Pb. A general result is that with the improved resolution of the new instrument, some new levels have appeared and a few previously reported were not observed. Of some special interest is the 2.8-kev resonance in Na²³ which was definitely shown to have $J=1$, σ₀=380±10 barns. It was observed that the strength function drops about a factor of ten when two protons are added to Rb⁸⁷ to make Y⁸⁹.