Measurements of Thermal Dissociation of Hydrogen, Using Fast Protons

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Abstract
Experiments involving study of the angular scattering of kiloelectron-volt protons from atomic and molecular hydrogen targets have been used to measure directly the fraction of hydrogen gas dissociated in equilibrium with hot tungsten. The state of the hydrogen gas in a tungsten furnace is determined by analyzing the scattered incident particles which result from single collisions between the incoming protons and the hydrogen gas in the furnace. In particular, the number of H— ions among the scattered particles is a measure of the molecular hydrogen density, since H— ions cannot be created in single collisions between protons and hydrogen atoms. Under the present experimental conditions it was possible to achieve a fraction dissociated of over 87.5% at a furnace temperature of 2380°K and still higher fractions at higher temperatures. These measurements are made at hydrogen pressures of the order of 10—2 Torr. The practical conditions under which an atmosphere of highly dissociated hydrogen can be created are described and it is pointed out how the dissociation fraction and also the density of the hydrogen can be directly measured in the otherwise inaccessible interior of the gas. These measurements using a proton beam probe do not require that the pressure or temperature of the hydrogen be known and, in fact, do not require thermal equilibrium conditions.