Energy Spectra of Neutrons Emitted Followingπ−Capture in C, A1, Cd, Pb, and U

The neutron emission from the capture of stopped ${\pi }^{-}$ mesons in C, Al, Cd, Pb, and U has been studied using a time-of-flight detector. The energy spectra are characterized by a low-energy "evaporation" part, and a high-energy component due to the "direct" neutron emission. The general features of the "direct" neutron emission are similar for all the substances studied, with approximately 2 neutrons per ${\pi }^{-}$ capture. In contrast, the relative yield of the low-energy component increases markedly in the heavier nuclei. The neutron multiplicities in the energy range from about 1.8 to 150 MeV were 2.8±0.3, 3.2±0.3, 3.6±0.4, 3.5±0.4, and 5.0±0.5, for C, Al, Cd, Pb, and U, respectively. The total kinetic energy in neutron emission was about 68, 74, 80, 69, and 100 MeV for C, Al, Cd, Pb, and U, respectively. In the case of Cd the data are sufficiently complete to give a good account of the energy balance.