Measurements have been made of the energy spectra of neutrons inelastically scattered from 14.8 Mev into the interval 0.5-4 Mev. Carbon, aluminum, copper, tin, and lead scatterers were used. 100-kev deuterons were extracted from a cyclotron and allowed to strike a target of tritium absorbed in zirconium. The resulting reaction ${\mathrm{T}}^3(d, n){\mathrm{He}}^4$ (17.7 Mev in the center-of-mass system) yielded a 14.8-Mev neutron accompanied by a recoil 3-Mev alpha particle. A scintillation counter within the vacuum system, subtending a solid angle of $\frac{4\pi }{100}$ at the target, detected recoil alpha particles with ∼100 percent efficiency, delivering a fast signal whenever a neutron started on a path within a cone chosen to avoid scattering material for a distance of several meters. Within the cone and close to the target a scatterer was placed. The inelastically scattered neutrons emerged from the scatterer with approximate isotropy, while few elastically scattered neutrons were deflected through large angles. A proton-recoil neutron counter placed at ∼90° to the cone axis was thus prevented from detecting almost all undesired neutrons. The distance from the scatterer to the counter was 50 to 100 centimeters, and neutron energies were obtained from the measured flight times over this path length, with the recoil alpha signal serving as a time zero. The flight times, which were from 20 to 65 millimicroseconds, were measured by a time analyzer having nine 4.7×${10}^{-9\mathrm{}}$ second channels, recording directly on mechanical registers. Experimentally, neutron energies after scattering could be approximated by number/unit energy $E=E\exp (-\frac{E}{T})$ with $T$, the "nuclear temperature" in Mev obtained from the raw data being: Pb, 0.75; Sn, 0.62; Cu, 0.84; Al, 1.06; C, 0.93. These results are in general agreement with photographic plate data. The experimentally observed angular distributions were isotropic within the limits of error of ∼15 percent. Over-all limits of error of ±15 percent in the nuclear temperatures are assigned.

• Received 25 May 1954

DOI:https://doi.org/10.1103/PhysRev.95.1235