Gamma-ray spectra have been measured at the 27-keV ($2^{-}$) and the 49-keV ($1^{-}$) resonances of ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}(n, \gamma ){}_{}{}^{20}{}_{}{}^{}\mathrm{F}$. The $E1\mathrm{}$ transition to ground is virtually absent at both resonances, while the other $E1\text{'}\mathrm{s}$ have strengths that appear normal when compared with heavier nuclei in which the radiation widths are proportional to level spacing. A description is given of the two-parameter instrument by means of which it is possible to measure simultaneously the neutron energy (flight time) and gamma-ray pulse-height spectra for radiative neutron capture.

• Received 30 November 1964

DOI:https://doi.org/10.1103/PhysRev.138.B20