Interference Phenomena in the Scattering of Slow Neutrons

Transmission measurements of the neutrons absorbed by cadmium (C neutrons) are described which show that the total cross sections for various elements are dependent to a marked degree upon the physical and chemical state of these elements. This is shown by (1), the transparency of single crystals as compared with the same material in a polycrystalline form, and (2), the nonadditivity of the cross sections for chemical compounds and alloys. The de Broglie wave-length of the C neutrons is such that the above effects can be interpreted in terms of interference. The nature of the results is well illustrated by the SiO₂ measurements. The cross section for the molecule computed from measurements on the component elements is 10.5. The cross section for the molecule in sand is 8.8±{}1; in fused quartz 8.1±{}1; and in single crystals of quartz 4.3±{}0.6, all in units of 10^-24 cm².