US3287592A - Particle accelerator assembly having a beryllium-tritium composite target - Google Patents

Description

N 22, 1966 J.J.H1RSCHFIELD ET AL PARTICLE ACCELERATOR ASSEMBLY HAVING A BERYLLIUM-TRITIUM COMPOSITE TARGET Filed Dec.

5 8 E 9 I H a E" w 2 mm a Na nm 4 I! M //Jl\ A 6 up 9 m H 4 5 1 0 4 2 7 M 0 (am-ll n 2) 3 I L Q. 2 9 2 E I 2 8 3 7 m 2 M E; 2 M a J E .2: an a 5 w 8 Mm Mm 3 l F L United States Patent Office 3,287,592 Patented Nov. 22, 1966 3,287,592 PARTICLE ACCELERATOR ASSEMBLY HAVING A BERYLLlUM-TRITIUM COMPOSITE TARGET Jule J. Hirschfield, Brookline, and Bernard A. McDewell, Billerica, Mass., assignors to High Voltage Engineering Corporation, Burlington, Mass., a corporation of Massachusetts Filed Dec. 14, 1961, Ser. No. 159,360 1 Claim. (Cl. 313330) This invention relates to particle accelerator targets and more particularly to novel combinations and arrangements thereof directed toward increasing target life and utility.

Most commonly, man made radiation is produced by bombarding a metal target with a high intensity charged particle beam. The nature of the radiation, that is X-ray, gamma ray, neutron or the like, as well as its wave length and energy are determined by the character of the charged particle beam and by the composition of the metal target. For example, high frequency X-rays can be produced by bombarding a tungsten target with a high energy electron beam, while neutrons will radiate in quantity from a deuteron bombarded beryllium target. When it is desired to utilize the charged particle beam itself, a target that is transparent to the charged particles (more properly a vacuum window) is used. The beam generated by a particle accelerator then may have various applications and may produce various types of radiation depending upon the composition of the target that intercepts it. It is apparent that if a plurality of such targets were readily interchangeable in a radiation generating system, greater utility and economy of time and money would result. This, however, is not the case in the current state of the tart. Since the charged particle beam must be generated in a vacuum system the target to which it is directed conventionally constitutes a vacuum sealed closure of the output aperture of the particle accelerator. Interchanging targets, then, means taking the machine out of operation and breaking the vacuum. Such a procedure is particularly objectionable when the device is used for neutron activation analysis where continuous monitoring of the specimen under examination is often required. Furthermore, such neutron activation analysis requires radiation producing apparatus of considerable flexibility and entails the use of various targets. If any appreciable range of elements is to be examined, high and low energy neutrons as well as so-called fast and slow neutrons mus-t be generated. A copious supply (10 n./se-c./cm. of relatively low energy neutrons, that is in the 3 to 5 mev. range, may be produced by bombarding a beryllium target with a 1.3 mev. deuteron beam. Such a beryllium target is virtually indestructa-ble and the neutron output therefrom is constant and dependable. A 1.3 mev. deuteron beam may be supplied by a conventional particle accelerator such as a Van de Graafi generator or a linear accelerator. While such a neutron supply is adequate for analysis of the majority of elements, some elements, such as oxygen, require irradiation by high energy neutrons, that is in the order of 12 mev., to activate them. Since it would require a prohibitively expensive atomic reactor to generate a deuteron beam adequate to produce 12 mev. neutrons by beryllium bombardment, the use of a beryllium target is not feasible for such an application. Alternatively, a target fabricated of tritium may be used. Such a target consists of titanium or Zirconium into which tritium gas has been diffused and has the property of being capable of producing the desired high energy neutrons from bombardment by a deuteron beam having as low an energy as 0.1 mev. However, unlike the beryllium target which has an almost infinite life and constant neutron output, the tritium target is characterized by diminishing output and short life. Since tritium escapes readily when the target is heated by the impinging deuteron beam, the target decreases in output by almost 50% in forty minutes at kv. and 1 ma. current. Such a short life obviously places severe limitations on the continuous use of such a target. Ideally then, neutron activation analysis apparatus would include a particle accelerator having a beryllium target for normal use, a plurality of tritium targets for special applications and convenient means for switching therebetween. Similarly, like ohjectives prevail in other areas of radiation generation. For instance, in therapeutic X-ray devices it would be desirable to have a plurality of X-ray targets adapted to generate X-ray beams of various configurations and to be able to selectively place such targets in intercepting relationship with the electron beam without disrupting the vacuum system.

Accordingly, it is a principal object of our invention to provide a new and improved particle accelerator target assembly.

It is another object of our invention to provide, for use with a particle accelerator, a composite target assembly whereby any one of a plurality of discrete target members may be positioned in intercepting relationship with the accelerator beam without disturbance to the vacuum system thereof. 1

It is yet another object of our invention to provide, in a particle accelerator for use in neutron activation analysis, a composite target assembly adapted to provide, through the bombardment of various portions thereof by a deuteron beam, the generation of neutrons having at least two discrete energy levels.

It is still another object of our invention to provide, in a particle accelerator for use in neutron activation analysis, a neutron producing target having longer life and greater versatility than has heretofore been possible.

And still another object of our invention is to provide, in a particle accelerator for use in neutron activation analysis, a composite target assembly having a segment of beryllium and at least two segments of tritium as integral parts thereof, together with means for selectively positioning such segments in intercepting relationship with the particle accelerator beam.

' These objects, together with other features and advantages of our invention will become more readily apparent from a reading of the following detailed description in conjunction with the accompanying drawings. While such description and drawings relate to neutron activation analysis apparatus in general and although specific structure is referred to, our invention is not to be construed as being limited thereto, the essence thereof being adapted to a wide variety of applications.

In the drawings wherein like elements are given like reference numerals throughout:

FIGURE 1 illustrates one embodiment of our invention as employed in neutron activation analysis apparatus;

FIGURE 2 is a sectional view of FIGURE 1 at 2-2;

FIGURE 3 is a detail of the target assembly comprehended by our invention; and

FIGURE 4' is a section taken through FIGURE 3 at 44.

Referring now to FIGURES 1 and 2, there is illustrated a target assembly of the type comprehended by our invention in combination with neutron activation analysis apparatus. In operation, particle accelerator 6, in this instance a Van De Graaif generator, generates a deuteron beam that is projected through conduit 13. Conduit 13 constitutes a continuation of the particle accelerator vacuum system and is terminated by target assembly 12. Target assembly 12 comprises a plurality of discrete target segments arranged to selectively intercept the deuteron beam and will hereinafter be described in greater detail with reference to FIGURES 3 and 4. Particle accelerator 6 and the neutron beam generated thereby have a fixed frame of reference with respect to the sample being analyzed, said deuteron beam at all times being directed to pneumatic tube 11 wherethrough said sample is made to pass. The deuteron beam, impinging on one of the targets of target assembly 12 produces a supply of neutrons which irradiate the sample residing in pneumatic tube 11. A container may be filled with water or paraflin should so-called slow neutron irradiation be desired. C-onduit positioning member 9 is mounted on support member 8. Target selection is effected by placing conduit 13 into the one of the recessed notches 14, 15, 16 of conduit positioning member 9 that corresponds to the desired target. Bellows members 7 allows deflection of conduit 13 while maintaining the de-- sired vacuum therein. While it is also feasible to obtain target selection by electrostatically deflecting the deuteron beam, and while our invention is intended to encompass any such methods, the simplicity and dependability associated with mechanically positioning the target with respect to a fixed beam represents a preferred embodiment for most applications.

Target assembly 12 is illustrated in detail by FIGURES 3 and 4. Target frame has a plurality of openings 26 are provided with flanges 40 adapted to seat the target member in flush relationship therewith. Openings 26 are further provided with threaded portions 41 whereby annular nuts 31 secure the target member therein. Indium seals insure a vacuum tight engagement of said target members. In the present illustrative embodiment target members 27 and 28 are of tritium and target member 29 is of beryllium. Any type of target and any combinations thereof may be used, however, without departing from the scope of our invention. The end of conduit 13 is flanged to facilitate the attachment thereto of the target assembly, the vacuum seal 34 is provided to maintain the vacuum system. The target under deuteron bombardment is cooled by pumping water or other liquid coolant through pipes 32. Annular spacer 23, gaskets 35, 39, and end plate 21 provide means for the coolant to circulate past the target. A vacuum seal 38 is required for pipes 32 since they reside within the conduit vacuum. The entire assembly is bolted together by means of bolts 36.

While a particular embodiment of our invention has been shown and described, it is apparent that changes and modifications may be made without departing from the invention in its broader aspects, and therefore the aim of the appended claim is to cover all such changes and modifications as fall within the true spirit and scope of the invention.

We claim:

In combination with a particle accelerator adapted to generate a charged particle beam, means for generating high energy neutrons comprising (1) A composite target assembly having demountable target members, said tar-get assembly constituting a vacuum tight closure of the output aperture of said particle accelerator and being in substantially transverse relationship with said charged particle beam, said target assembly including:

(a) a frame member having a plurality of circular apertures therein, said apertures being threaded and having an inner flange therearound,

(b) a plurality of disc target members each adapted to reside within one of said apertures in abutting relationship to the flange portion thereof, said disc tar-get members comprising one beryllium target and at least two tritium targets,

(0) an annular vacuum seal member associated with each said aperture adapted to hermetically seal a target therein, and

(d) an annular threaded nut associated with each said aperture adapted to secure a target in compressed relationship to its associated vacuum seal;

(2) means for transversely displacing said target assembly to selectively place discrete target members in intercepting relationship with said charged particle beam, and;

(3) means for circulating a coolant fluid in contiguous relationship to said target assembly.

References Cited by the Examiner UNITED STATES PATENTS 2,559,526 7/1951 Van de Graafl et al. 3l3-330 2,816,242 12/1957 Goodman 313-6l5 2,959,700 11/1960 Campanile 31356 2,996,618 8/1961 Goodman et a1 313615 JAMES W. LAWRENCE, Primary Examiner.

RALPH G. NILSON, Examiner.

W, F. LINDQUIST, S. SCHLOS SER Assistant Examiners.

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