Fast Neutron Resonance with Nitrogen

Studies of the ${}_7{}^{}{}_{}{}^{}\mathrm{N}_{}^{14}{}_{}{}^{}\mathrm{}(n,a)\mathrm{}{}_5{}^{}{}_{}{}^{}\mathrm{B}_{}^{11}{}_{}{}^{}$ reaction indicate the emission of heavy particle groups possibly as a result of resonance transmutation by fast neutrons from a Ra - Be source. When a nitrogen absorber is placed before the nitrogen detector, the heavy particle groups apparently do not appear. Upon interposition of carbon as a retarding material between nitrogen absorber and detector, the reappearance of some of the groups in question occurs. This behavior would appear to indicate that nitrogen has a larger than normal probability to undergo transmutation by certain fast neutron groups. Two interpretations suggest themselves: (1) the experimental points, while based on more than 100,000 pulses, possess statistical fluctuations sufficient to produce the observed apparent resonance phenomena for fast neutrons or (2) nitrogen has a fast neutron absorption cross section of the order of 60×${10}^{-24\mathrm{}}$ ${\mathrm{cm}}^2$, much larger than the theoretical upper limit of about 0.7×${10}^{-24\mathrm{}}$ ${\mathrm{cm}}^2$. The resonance interpretation is supported by supplementary evidence. Further development of these techniques should make it possible to (1) estimate widths of nuclear levels, (2) measure nuclear energy levels, (3) check the reality of observed groups, and (4) determine which isotope is responsible for a group. Additional investigation of the subject is indicated.