No abstract

Energy-storing molecular products of radiation in liquid hydrogen are examined from the point of view that the explusion of potential energy in the form of such products may lead to lower design weights for nuclear rockets. It is found that a significant fraction of the energy deposited by radiation in liquid hydrogen is stored temporarily through the dissociation and excitation of H2 molecules" Experimental and theoretical results are consistent with a rate of dissipation of such energy into thermal motion which is much slower than the rate at which the radiation products are expelled from the tank. It is shown that, if this is the case, relatively high levels of infrared radiation are to be expected but that such energy will not rapidly be translated into thermal motion. It is concluded that, insofar as radiation heating of the propellant is a significant design factor, further consideration should be given to radiation-induced reactions in liquid hydrogen and that any radiation-heating experiments should be interpreted in terms of possible energy-storage effects" 3 Blank page REPORT SUMMARY Hydrogen-propelled nuclear vehicles play a leading role in presently envisaged space missions. Therefore, the processes associated with radiation-heating in liquid hydrogen are worthy of attention. Of particular interest from the standpoint of propellantshield design is the formation of energy•=»storing molecular species through which the production of actual thermal energy is temporarily postponed. Consideration of potential energy expelled from the system in the form of such species may lead to lower overall design weights, owing to less stringent provisions for shielding, pressurevessel construction, and/or boil-off" The object of the present study is to determine whether an appreciable amount of the energy deposited by radiation is stored in radiation products and whether such products survive in the liquid long enough to be expelled from the system. In realistic cases most of the radiation products are formed near the exit, and the time required for their expulsion is only about 20 seconds.Energy deposited in liquid hydrogen by neutral radiation is initially transferred to recoil protons or Compton-scattered electrons in the case of neutrons or gamma rays, respectively.When such charged particle pass through the hydrogen, which is normally almost entirely in the H2 ground state, approximately equal amounts of energy go into the production of H-atom pairs.5 through the formation of the repulsive •^s^ H2 state and into the production of Hg ions. By means of reactions such as HJ + H2=^'H+ -h H : H^ -f e" =^H* + H, the ionization process leads indirectly to further dissociation and excitation. Through ionic ajid dissociative reactions alone, about 43^ of the energy deposited is temporarily stored in the production of H atoms and excited Hg molecules. Most of the remaining energy is initially released by the ejection of H atoms from repulsive molecular configurations. The total amount of energy storage could be sub...