United States Patent m [in 4,145,629 Devienne [45] Mar. 20,1979 [54] SOURCE OF IONS OF HIGH MASS, [56] References Cited ESPECIALLY IONS OF URANIUM OXIDE FOREIGN PATENT DOCUMENTS uo2 2212044 7/1974 France. [76] Inventor: Fernand M. Devienne, 117 La Primary Examiner—Rudolph V. Rolinec Croisett, 06400 Cannes, France Assistant Examiner— Darwin R. Hostetter Attorney, Agent, or Firm—Flynn & Frishauf [21] Appl. No.: 707,319 [57] ABSTRACT An evacuated chamber contains a source of primary ions, a charge-exchange box, the inlet of which is sup- [22] Filed: Jul. 21,1976 plied by the primary ion source and delivers at the outlet a primary molecular or atomic beam which is at [30] Foreign Application Priority Data least partially neutralized, a target of the material to be ionized which intercepts the emergent primary beam Jul. 25, 1975 [FR] France 75 23353 from the charge-exchange box and which is of such Dec. 18, 1975 [FR] France 75 38913 geometry that the primary beam undergoes multiple reflections from the target, the target being placed [51] Int. C1.2 H01J 27/00 within a chamber which is brought to a potential oppo- [52] U.S. Q 313/230; 313/231.3 site to that of the polarity of the ions produced. [58] Field of Search 313/230, 231, 231.3, 313/362, 363 14 Claims, 4 Drawing Figures U.S. Patent Mar. 20, 1979 Sheet 1 of 2 4,145,629 FIG. 1 U.S. Patent Mar. 20, 1979 Sheet 2 of 2 4,145,629 FIG. 3 FIG. 4 4,145,151 Should it be desired to remove the primary ions as SOURCE OF IONS OF HIGH MASS, ESPECIALLY these latter pass out of the charge-exchange box, provi- IONS OF URANIUM OXIDE U02 sion is advantageously made for primary ion deflecting plates consisting of electrodes brought to a potential This mvention relates to a source of ions of high mass, 5 such as to collect or deflect the primary ions to a suffi- especially ions of uranium oxide UO2. cient extent to ensure that these latter do not reach the As is already known, it is necessary in many applica- target, the neutral particles constituting the molecular tions to produce ion sources of high intensity, these ions jet or beam being unmodified by the presence of these being of high mass such as, for example, the ions con- deflecting plates. taining uranium, among others the uranium oxide UO2. 10 In ion sources of the type above described, the beams In fact, these ion sources containing uranium can be put of neutral particles which arrive on the target produce to use, provided that they are of sufficient intensity, in molecular sputtering of the atoms or molecules of the isotope separation processes in which the separation is target, only part of these latter being converted to ions. carried out from uranium in the state of an ionic com- The greater part of the beam of neutral particles is re- pound. 15 flected from the target without being subsequently em- As will hereinafter become apparent, the ion source ployed and its energy is thus lost. in accordance with the invention makes it possible to In order to obtain ion sources of maximum intensity, obtain ion beams of high mass and of relatively high 4 2 especially sources of ions of uranium oxide UO2 ", it is current density of the order of several mA/cm . an advantage to ensure that the beam of neutral parti- The ion source in accordance with the invention 20 cles which impinges on the target is utilized with the comprises a source of primary ions, for example argon maximum degree of efficiency. ions formed by any suitable means such as high-fre- To this end, the structural design of the source and of quency heating, a charge-exchange box, the inlet of the chamber containing said source is such that the jet which is fed by said source of primary ions, said box being intended to deliver at the output an atomic or 25 of neutral particles undergoes multiple reflections from molecular jet of elements corresponding to the at least the target in order to improve the conversion efficiency partial neutralization of the primary ions, a target which of said ion source by increasing the number of impacts. intercepts the emergent molecular jet from the charge- In other words, the geometrical configuration of the exchange box and is of such geometry that the atomic target is such that the atomic jet undergoes multiple or molecular jet undergoes multiple reflections from the 30 reflections from said target before being extracted from target, said target being intended to contain the com- the chamber which contains said target. In an illustra- pound from which it is desired to produce the highmass tive embodiment of the invention, the target has a sub- ion beam and finally a chamber which is brought to a stantially cylindrical structure and can accordingly positive potential opposite to that of the polarity of the constitute an internal lining of the chamber. The genera- secondary ions produced and which surrounds said 35 tor-lines of said cylindrical chamber are substantially target. perpendicular to the direction of the primary jet and the normal to the wall of the target on which the initial The primary beam which is at least partially neutral- ized detaches ions from the target when it bombards the impact of the primary jet takes place is inclined with surface of this latter, said ions being extracted from the respect to the direction of said primary jet at an angle 9 target by means of an extraction potential applied to the 40 of the order of 60°, for example. chamber which surrounds said target. In accordance with one mode of execution of this The determining advantage which arises from the use illustrative embodiment of the ion source in accordance of a molecular (or atomic) jet which is neutral or at least with the invention; that portion of the target on which partially neutralized lies in the elimination of the space the initial impact of the primary jet of neutral particles charge phenomenon which takes place when the target 45 takes place is constituted by two walls forming a dihe- is bombarded with an ion beam such as, for example, in dron, the edge of which is perpendicular to the genera- conventional methods of cathodic sputtering. The exis- tor-lines of the cylinder. In order to ensure that the ions tence of this space charge prevents the ions of the pri- produced as a result of impact of the molecular or mary beam from reaching the surface of the target with atomic jet of netural particles on the target are extracted a high flux, thus resulting in a concomitant reduction of 50 more effectively, it is an advantage in accordance with the intensity of the secondary ion flux of high mass the invention to place an electrode having a negative emitted by said target in accordance with the invention. potential with respect to the target in the vicinity of the The primary beam employed is thus either composed exit of the beam of secondary ions produced by impact of neutral particles or of a mixed beam of neutral parti- of the primary neutral-particle jet on the target. cles and ions with a proportion of ions which can be 55 It is readily apparent that the geometrical structure of variable according to the nature of the substance. the source contained in the chamber can be varied with In a preferred alternative embodiment of the inven- a view to obtaining multiple reflections and can have, tion, a grid brought to a negative potential is placed in for example, the shape of a torus or of a cone frustum the vicinity of the target, thus making it possible to which is open at both ends. accelerate and orient the ions towards the outlet of the 60 Further characteristic features and advantages of the chamber in which the target is placed. invention will become more readily apparent from the The charge-exchange box in which neutralization of following description of examples of construction the primary ion beam takes place is of a conventional which are given by way of explanation without any type as described, for example, in the work by M. De- limitation being implied, reference being made to the vienne: "Jets mol6culaires de hautes et moyennes ener- 65 accompanying drawings, wherein: gies" (Molecular jets of high and medium energies) FIG. 1 is a general diagrammatic representation of a (published by Laboratoire de Physique Moleculaire des form of construction of the ion source without the mul- Hautes Energies 06 —Peymeinade — France, 1972). tiple target reflection feature of the invention; 4,145,629 4 FIG. 2 is a general diagrammatic representation of an The intensity of the ion beam emitted by the target 2 illustrative form of construction of the ion source in depends on the radius of the chamber 4, on the arrange- accordance with the invention, in which the incident ment of the target 2 and of course on the target itself, primary beam undergoes successive multiple relfec- the physical and chemical characteristics of which are tions; 5 of considerable importance in regard to the intensity of FIG- 3 is a diagrammatic sectional view of a particu- the beam 18, namely in particular the secondary ionic lar form of target limited by two concentric circular emission ratio of the target and also the bombardment cylinders; energy. FIG. 4 illustrates another possible form of target When negative ions are obtained as a result of molec- having a structure in the shape of a cone frustum.