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

Abstract

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 ${\mathrm{Na}}^{23}$, ${\mathrm{Al}}^{27}$, ${\mathrm{P}}^{31}$, ${\mathrm{K}}^{39}$, ${\mathrm{K}}^{41}$, ${\mathrm{Rb}}^{85}$, ${\mathrm{Rb}}^{87}$, ${\mathrm{Sr}}^{86}$, ${\mathrm{Sr}}^{88}$, ${\mathrm{Y}}^{89}$, ${\mathrm{Bi}}^{209}$, 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 ${\mathrm{Na}}^{23}$ which was definitely shown to have $J=1\mathrm{}$, ${\sigma }_0=380\mathrm{}\pm 10$ barns. It was observed that the strength function drops about a factor of ten when two protons are added to ${\mathrm{Rb}}^{87}$ to make ${\mathrm{Y}}^{89}$.