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1297reported value of 2.97 Mev. A lower-energy component with a relative abundance of 1.5 percent has its upper energy limit at 0.92 Mev. No strong evidence appeared for the existence of a beta ray at an intermediate energy, as previously reported. 3 The energies of certain gamma rays are observedThe total reflection and selective attenuation properties of mirrors for neutrons were used to obtain essentially higher order free reflections of a beam of reactor neutrons from a quartz crystal. An arrangement of mirror, crystal, and sample, in series was used to measure the total cross section of Au, Ag, In, Ni, and NiO as a function of neutron wave length over intervals in the region between 0.7A and 4.6A. The results on the strong absorbers Au, Ag, and In were analyzed into absorption and scattering contributions. The absorbers exhibited essentially the 1/v characteristic expected. The scattering and absorption cross sections of Au, Ag, and In are compared with previously reported values. For the strong scatterers Ni and NiO, the total scattering, ordered scattering, and disordered scattering cross sections, and the Debye temperature were derived from the energy dependence of the total cross section. The ordered scattering cross section per Ni nucleus was found to be 13.1 ±0.3 barns. The capture and

The neutron polarization cross section of iron has been measured as a function of energy from 0.7 to 3.3 A by two methods: using the single transmission effect in a block of poly crystalline iron at energies selected by a quartz crystal monochromator; and using a single crystal of magnetized magnetite to analyze the beam emerging from the iron polarizer, the magnetite crystal itself serving as monochromator. The measured values are compared with those of other observers and the theoretically expected values. These are found to agree fairly well within the limits of accuracy of the measurements and existing knowledge of the wave function of the iron 3d shell. The two techniques were used also to determine the average polarization (32 percent) as seen by a 1/v detector in a beam of reactor neutrons emerging from a 4-cm thick polarizing block of iron. Problems and techniques associated with the measurement of the average polarization of a continuous spectrum are discussed. A simplified experimental treatment of the problem of beam "hardening" is described. A description is given of the use of the magnetic resonance method in conjunction with a singlecrystal magnetite analyzer for the measurement of neutron polarization. A. INTRODUCTIONM ANY experimental studies 1 " 12 of the polarization of slow neutrons have been made for the purpose of verifying the theory 13-31 of scattering, polarization, and depolarization of neutrons passing through crystalline magnetic materials. Some of the experiments measure the energy dependence of the change in the total cross section upon magnetization of a polycrystalline sample of iron. The rotating shutter 8 and the pulsed cyclotron 9 time of flight methods have been used for the velocity selection. We have used the higher resolution of the single-crystal spectrometer to measure the polarization cross section as a function of energy from about 0.7 to 3.3A, by two methods: using the single transmission effect in a block of polycrystalline iron at energies selected by a quartz crystal monochromator; and using a single crystal of magnetized magnetite to analyze the beam emerging from the iron polarizer, the magnetite crystal itself serving as monochromator. In the first of these methods the polarization cross section is deduced from the change in the intensity of the beam transmitted by the polarizer on magnetization. We have developed the application of the second method, in which the polarization cross section is deduced from the value of the polarization of the beam emerging from the polarizer, as determined from the known analyzing properties of the magnetite crystal. This method is simpler since the problem of lack of complete magnetic saturation is much less severe. Our results exhibit the discontinuities in the polarization cross section due to crystal structure in greater detail than previous work of other observers. The results are found to agree with the theoretically expected values 20 within the limits of accuracy of the measurements and existing knowledge of the boundary co...

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The dependence of the capture cross section of polarized Mn 65 nuclei for polarized neutrons upon relative orientations of incident and bombarded particles has been directly observed. The target material was the paramagnetic substance, manganous ammonium sulfate, which is known to have a large hyperfine structure coupling. It was placed in a magnetic field of 2350 oersteds at a temperature of 0.20°K. Under these conditions the polarization of the paramagnetic electrons is about 85 percent. Because of the large effective magnetic field created by the paramagnetic electrons at the Mn nucleus, the nuclei should achieve a polarization of 16 percent. The 2.6-hour activity of the residual nucleus, Mn 56 , was measured after the sample had been bombarded with a beam of slow neutrons polarized to the extent of 32 percent by passage through magnetized iron. The activity for neutron polarizing field and sample polarizing field parallel was found to be 3.4 percent less than for the fields antiparallel. The difference in the two activities was found to depend upon the sample temperature in accordance with theory. The difference was found to be unaccompanied by a corresponding change in sample transmission. These results are interpreted to mean 1hat the change in sample activity was due to the dependence of the capture cross section of the polarized Mn nuclei upon the relative orientation of the interacting particles. The observations are discussed in terms of available information about the energy level system of the compound nucleus, Mn 56 .