Measurement of Cross Sections with Neutrons as Targets

The purpose of the experiment described in this report was to test the use of the Chew-Low extrapolation technique for the measurement of cross sections with unstable particles as targets. The test was performed by using the Chew-Low method to measure proton-neutron total cross sections ${\sigma }_{\mathrm{pn}}$ with protons of 161-MeV energy incident on deuterium, and comparing the results thus obtained with values of the neutron-proton cross section previously determined from the scattering of projectile neutrons on hydrogen targets. At two values of the effective incident energy, 125 and 168 MeV, the values found were ${\sigma }_{\mathrm{pn}}=42.9\mathrm{}\pm 5.6$ mb and ${\sigma }_{\mathrm{pn}}=40.9\mathrm{}\pm 5.9$ mb, respectively. These values are in sufficiently good agreement with the corresponding values of ${\sigma }_{\mathrm{np}}$, particularly at the higher energy where the extrapolation distance is shorter, to give confidence in the Chew-Low method for the determination of unknown cross sections.