Patent Number: 043604951
Section: summary

The present invention relates to a target arrangement for spallation-neutron-sources, wherein target material is continuously present at the point of incidence of a proton beam. With the most recent developments in acceleration technology of high proton streams (with the range of the order of mA) it has basically become feasible to utilize a spallation (nuclei evaporation) of heavy elements by energy-rich protons (approximately 1 GeV) for the construction of neutron-sources, which neutron-sources are equivalent, or even superior, in their thermal neutron-flow to a high flux reactor. Hereby, in comparison with such high-flux reactors, basic advantages are provided, for example, waiver of fissionable materials, substantially reduced production of radioactive, noble gases, and a substantially reduced potential of endangering the environment, because no critical arrangement is present. Such spallation-neutron-sources could in future replace experimental reactors to a considerable extent and could also gain increasing importance as predecessors for electrical breeder installations. However, the problem of heat removal from the target needs to be satisfactorily resolved. The quantities of heat per unit, of the order of about 10 MW/l, attendant in a spallation target, lead to a rate of heating of the material of 10.sup.4 K/s and up, and, thus, present substantial difficulties. Effective spallation-sources have not been built as yet. Pulsed neutron-sources, which can be considered predecessors, utilize water-cooled stationary target arrangements with quantities of heat per unit of several kW/l in a timewise mean (J. M. Carpenter, Nuc. Inst. Met. 145 (1977), pages 91-112). In accordance with a project proposal of 1966 [Bartholomev G. A and Tunnicliffe P. R., "The AECL-Study for an Intense Neutron Generator", Chalk River, AECL-2600 (1966)] it is suggested to introduce a proton beam vertically into a flowing target comprising liquid lead-bismuth-eutecticum, which is pumped at a high velocity (about 5 m/s) through a circuit. The circuit includes the target and a heat exchanger. Thus, a considerable quantity of liquid radioactive metals (several tons) must be kept in circulation. Up to the present, this concept has been considered to be the only solution of the problem. However, such an installation has the following drawbacks: The proton beam, of an energy of 1 GeV and several milliamperes electric strength, has to be deflected into a vertical direction in order to avoid utilization of a stationary window into which a beam is shot (which window would be destroyed after a short period of time). This is difficult to attain and involves considerable effort. The liquid metal circuit is dependent upon utilization of Pb-Bi-eutecticum. During spallation this causes production of the poisonous mercury isotope 194-Hg which is volatile and of long life, and production, by neutron capture in the bismuth, of the particularly undesirable polonium, undesirable because .alpha.-active and volatile. Both could be avoided when using heavy metals with a high melting point, such as W or Ta. For producing particularly high neutron fluxes it is desirable, under certain circumstances, to utilize the materials Th or U-238 which are fissionable by fast neutrons. Due to the respective high melting points, these can be used, again, only in their solid state. The liquid metal circuit is technically very involved, very expensive, and, due to the stored energy quantity, potentially dangerous in the event of fracture of the highly strained conduits. A retention of the reaction products in the liquid is not assured. It is accordingly an object of the invention to provide a target arrangement which assures to a high degree flexibility in the selection of the target material and in which the target is a solid body so that the reaction products are retained to a large extent. It is further an object of the invention to reduce, in comparison with the liquid metal circuit, the technical complexity and to provide an arrangement which allows the horizontal introduction of the proton beam.