The Production and Properties of Low Temperature Neutrons

Abstract

Evidence has been found that (a) hydrogenous substances so cold that nearly all the molecules are in the ground state can cool only those neutrons whose kinetic energies are great enough to excite the molecules to their first state, e.g., the temperature of neutrons cooled by a crystal of such molecules at the absolute zero will approximate the temperature at which the specific heat begins to rise above the normal curve of the Debye type for crystalline specific heat; (b) the probability of energy loss to a liquid or crystal as a whole seems to be small; (c) for hydrocarbons, the limiting temperature for cooling neutrons appears to decrease with increase in length of the hydrocarbon chain. A neutron thermometer, using the absorption by boron, has been tested and calibrated approximately.