Some Experiments with Neutrons slowed down at different Temperatures

Abstract

Experiments are described comparing the effects of neutrons slowed down in paraffin wax at the temperatures of liquid nitrogen and liquid hydrogen with those obtained at ordinary temperatures. It is found that the absorption produced by certain substances increases as the temperature is lowered. The transformations produced in these substances also increase, but generally to a smaller extent, probably owing to more neutrons being absorbed in the paraffin: the exact figure depends on the thickness of the layer of cooled paraffin.A few experiments were also made substituting liquid hydrogen for paraffin wax (without change of temperature). The effect of this also appears to depend on the thickness of the layer, but it is not yet possible to draw definite conclusions.

Further experiments on the slow neutrons transmitted by cadmium: influence of the temperature of the slowing down medium

“…the liquid covering the block, as the space round the block was very thin, and the presence there of liquid hydrogen (density 0-07 g./cm. 3 ) was not found to produce any measurable change in the effects. Experiments by Westcott and Niewodniczanski (3) with boric acid solutions had shown that the slow neutrons emerging in the neighbourhood of the detector (D, Fig.…”

“…The medium in the Dewar vessel could be cooled by pouring in liquid nitrogen or hydrogen. Since liquid nitrogen might absorb the neutrons appreciably, the level was kept below the bottom of the detector during measurements, a little liquid being added frequently between exposures to keep the temperature low (3). With liquid hydrogen it was found preferable to work with -D lOcro.…”

“…It has been known for some time that when a neutron source is placed in a hydrogenous medium, a considerable proportion of the neutrons attains energies as low as the thermal energies of the atoms of the medium, so that the intensity of the effects which they produce depends on the temperature of this medium (1,2,3). Further, the "slow" neutrons obtained in this way are known to be selectively absorbed in certain substances, and, from this absorption, "groups" of neutrons have been identified (2).…”