Patent Number: 047602660
Section: summary

The invention relates to a device for the generation of thermal neutrons, including a housing containing a transportable neutron source and a moderator and having a neutron outlet opening. German Patent No. DE-PS 30 31 107 describes such a device. Normally, cost-intensive basic materials are needed for the production of neutron sources. Therefore, the need to improve the ratio of the source size to the number of thermal neutrons exiting the source housing has existed for a long time. However, the solutions to this problem suggested thus far by specialists continue to be unsatisfactory. It is accordingly an object of the invention to provide a device for the generation of thermal neutrons, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and which improves the ratio of the source capacity to the thermal neutrons produced With the foregoing and other objects in view, there is provided, in accordance with the invention, a device for the generation of thermal neutrons, comprising a gas-filled housing having a wall with inner surfaces and a neutron outlet opening, a spherical moderator housing disposed in the gas-filled housing, a transportable neutron source disposed in the spherical moderator housing, and cups formed of moderating material disposed between the moderator housing and the inner surface of the wall of the gas-filled housing, the cups being spaced at a given distance from the inner surface of the wall of the housing, from the moderator housing and from each other defining spaces between the cups, and the spaces between the cups defining openings directed toward the neutron outlet opening. The moderator cups serve both for the reflection of the neutrons primarily thermalized in the moderator housing and for the secondary moderation of a not inconsequential number of higher energy neutrons (E&gt;E.sub.therm) exiting the moderator housing. In accordance with another feature of the invention, the cups are coaxial to the moderator housing. This improves the reflection characteristic. In accordance with an added feature of the invention, the housing wall is in the form of another outer cup having free ends forming the neutron outlet opening. This improves the effect of the secondary moderation. In accordance with an additional feature of the invention, there is provided neutron-permeable material enclosing the moderating material. This is done if a liquid is used as moderator. In accordance with a further feature of the invention, there are provided brackets fastened to the cups and extended between the moderator housing and the inner surface of the wall of the gas-filled housing. This maintains the specified spacings between the cups. In order to form a neutron holder, in accordance with yet another feature of the invention, the spherical moderator housing or ball has a step-shaped canal formed in the center thereof defining at least one shoulder and ending at opposite sides of the gas-filled housing, the neutron source being supported on the at least one shoulder. Due to the fact that the canal passes through from one side of the housing to the other, on one hand it is easy to introduce the neutron source into the moderator sphere or to remove it therefrom and on the other hand, if the housing is disposed in a water seal of purifier, there is assurance that water will flow through the canal. In accordance with yet a further feature of the invention, the moderator housing has a center, the neutron outlet opening is disposed in a given plane and the cups are in the form of half shells having circular, ring-shaped openings in a plane running parallel to the given plane of the neutron outlet opening and intersecting the center of the moderator housing. The neutrons secondarily moderated or reflected in the vicinity of the cups thus reach the neutron outlet opening along the shortest path. In accordance with a concomitant feature of the invention, the gas-filled housing includes a cylindrical part, and including a collimator with a collimator inlet side and at least one collimation path, the collimator inlet side having a plastic or synthetic plating, coating or lining disposed thereon defining a free, open collimation path, and a plastic or synthetic plating, coating or lining disposed on the cylindrical part of the housing extending in a continuous taper to the collimator inlet side and forming part of the plating on the collimator inlet side. It is therefore seen that it is possible to use the device in combination with a collimator. With this embodiment, the higher energy neutrons still flowing in the direction toward the neutron outlet opening after their primary moderation, are also moderated secondarily, thus contributing to a further improvement of the efficiency of the neutron source. Other features which are considered as characteristic for the invention are set forth in the appended claims. Although the invention is illustrated and described herein as embodied in device for the generation of thermal neutrons, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.