US3246147A - Magnetic methods and apparatus for manipulating a beam of charged particles - Google Patents

Description

Aprii 12, 1966 s. F. SKALA 3,246,147 MAGNETIC METHODS AND APPARATUS FOR MANIPULATING A BEAM 0F CHARGED PARTICLES Filed Nov. 29, 1965 2 Sheets-Sheet 1 Z mus B 'mv UN\FORM MAGNETIC FIELD -e Xmas X AXlS Y mus (mus INVENTOE 23 SF. kALA ATTO NEY April 12, 1966 s. F. SKALA 3,246,147 MAGNETIC METHODS AND APPARATUS FOR MANIPULATING A BEAM OF CHARGED PARTICLES Filed NOV. 29, 1963 2 Sheets-Sheet 2 United States Patent MAGNETIC METHODS AND APPARATUS FOR MANIPULATING A BEAM OF CHARGED PARTICLES Stephen F. Skala, Chicago, Ill., assignor to Western Electric Company, Incorporated, New York, N.Y-, a corporation of New York Filed Nov. 29, 1963, Ser. No. 326,827 Claims. (Cl. 250-495) The present invention relates generally to methods of virtually extending at least one dimension of the effective cross section of a collimated beam of charged partices, and more particularly to methods and apparatus for uniformally irradiating troublesome product geometries. The general objects of the invention are to provide new and improved methods and apparatus of such character.

Penetrating radiation has, within the past few years, drawn widespread industrial attention as a processing tool. Modern applications of penetrating radiation include the preservation of food, the sterilization of drugs and medical supplies, the cross-linking of plastics to improve their characteristics, the polymerization of monomers to yield polymers with unique qualities, and the initiation of chemical reactions such as catalysis, isomerisation, halogenation and oxidation. The expanding horizons in the industrial utilization of radiation correspondingly increase the demands for more versatile techniques and devices for reducing radiation to a workable tool. 1

A significant problem area related to these demands is the manipulation of charged particles in a beam to increase the effective cross section thereof so that irradiation of substantial areas is facilitated. Many techniques, most of which involve static fields, have been devised for accomplishing this function, but all known techniques have significant limitations. For example, static fields utilized to enlarge or shape a collimated beam of charged particles must affect some charged particles within an instantaneous cross section to alter their course more than others, in order to obtain the varying degrees of angularity requisite for the desired shaping or enlarging of the beam. Even assuming a uniform particle density over a cross section of the initial beam, the resulting cross section of the shaped or enlarged beam invariably has a nonuniform particle density which gives rise to irregularities in the dose distribution and severely impairs the efiiciency of irradiation.

Uninhibited, a collimated beam of charged particles inherently has a nonuniform particle density, the densityat the center being much greater than that at the peripheral portions of the beam. The most widely used technique of enlarging the area of a beam and one which to a limited extent circumvents this problem, is a process termed scanning. This technique involves magnetically oscillating the beam laterally of itself and longitudinally along an opening in a scanning horn to sweep the'beam angularly and momentarily to the normally lowerdensity peripheral areas of the horn opening so that the resulting b am is of relatively uniform radiation density.

It is of course obvious that because the beam oscillates laterally of itself along the horn opening, the initial concentrated beam must be bent through continuously varying degrees of angularity to cover the entire length of the horn opening during a full sweep. To accomplish this, the strength as well as the position of the magnetic field must be continuously varied with precise accuracy.

In addition, since the concentrated beam occupies only a' small portion of the horn opening at any instant of time, the greater the degree of angular displacement of the concentrated beam, the greater the degree of spreading thereof over a portion of the'horn opening, and nonuniform particle density again results; Further, since the from maximum efiiciency and 3,246,147 Patented Apr. 12, 1966 particles at the peripheral areas of the horn are angularly projected against an object with respect to those at the center, the depth of penetration and therefore the radiation dosage is nonuniform over elongated areas traced across the object.

Therefore, it is an object of the present invention to provide a new and improved technique for virtually extending at least one dimension of the effective cross section of a collimated beam of charged particles, wherein the particles are bent through a constant angle and the strength of the magnetic field remains constant, with the result that the radiation density of the beam remains substantially unaltered during the virtual enlargement of the beam. Another object of the invention is to provide new and improved methods of such character, wherein the particle paths remain substantially parallel across the virtually elongated area so that spreading of the beam is uniform thereacross and a uniform dosage of radiation results; and wherein because the angular displacement of the beam is constant and the spreading uniform, one dimension of the beam cross section may thus be elongated practically without limit.

Still another object of the invention is to provide new' and improved methods of virtually elongating the cross section of a beam of charged particles, wherein all of the particles within the virtually elongated cross section of transverse movement of the product'relative to the beam so that the cross section of the beam may be virtually enlarged to encompass the entire product area to be;

irradiated.

A method accomplishing the above and other objects in accordance with the invention includes the steps of bending a collimated beam of charged particles through a substantial angle relative to the initial beam by arranging a magnetic field in the path thereof, and moving the magnetic field along the initial beam longitudinally thereof to cause the bent portion of the beam to sweep over an elongated area. 'In the more specific environment of irradiating a surface, the initial beam is projected generally parallel to and spaced from such'surface, and is bent toward the surface by the sweeping magnetic field of fixed strength so as to impinge on an elongated portion 'thereof.

The entire surface maybe irradiated by coordinating intermittent or continuous movement of the surface transversely of the-beam with reciprocal movement of the bent portion of the beam so that successive portions (intended to include contiguous portions and overlapping portions) of the surface in turn are irradiated on successive strokes of the bent beam.

In relation to another aspect of the invention, the irradiation of troublesome product geometries also constitutes'an acute problem in the utilization of penetrating radiation as a processing tool. One of the most perplexing product geometries encountered is a generally cylindrical cross section, such as elliptical, ovoidal, polygonal, or similar cross sections, or portions thereof. The difficulty in irradiating generally cylindrical objects stems minimum cost considerations, which require that the maximum available beam energy be absorbed by the object and that the radiation digiribution over the product area be as uniform as poss1 e.

In the case of cylindrical products this means that cylindrical surface at all points therearound for the same increment of time.

While this problem appears to be trivial when it is considered that the cylindrical surface could be rotated with respect to the source of the beam, or vice versa, to effect the desired result, it is not always convenient to rotate the object or the source, and their size and sensitivity often preclude this technique. It is also impractical to have a plurality of independent sources arranged about the circumference of the object, each directing a beam which is incident normal to succeeding contiguous portions around the circumference.

Many other techniques have been employed to alleviate this problem. One such techniquerequires the inversion of one-half of a beam so that the object is irradiated from two sides, thereby necessitating that the object be rotated. through an angle of only 180 to irradiate an entire circumference thereof. As before, however, it is not always convenient and sometimes impractical to rotate either the Object or the source.

It has also been proposed that a single beam, having a width substantially greater than the cylindrical object, be bent in increasing degrees, proceeding from the center of the beam to the peripheral portions thereof, so as to impinge normal to the surface all around a circumference of the object. This latter technique requires a magnetic field having a very critical involute configuration so that the strength thereof varies to bend each particle path with the same radius of curvature, the center of curvature for each successive path being disposed along a tangent to the object at the point of path intersection therewith, to enable successive particle paths to intersect normal to successive portions of the cylindrical surface. Another disadvantage of such a technique is that uniform distribution of the incident particles over the product area is invariably sacrificed to permit simultaneous irradiation of the entire outer surface. Also, the intensity of the incident radiation is nonuniform about the product as a result of nonuniformity of path lengths and air absorption. Finally the size of article that may be irradiated is limited from a practical standpoint, since the initial beam of radiation is limited as to the degree of enlargement obtainable, and must be much wider than the object irradiated.

It is therefore another object of the present invention to provide new and improved methods and apparatus for irradiating a curved surface so that charged particles impinge substantially normal to the surface at all points along the curve thereof. Still another object of the invention is to provide methods and apparatus of such character for irradiating a generally cylindrical surface, wherein a single beam may virtually be rotated about the article without moving either the beam source or the article, and wherein such rotation virtually elongates and expands the cross section of the beam without altering the uniformity of the radiation density thereof.

A further object of the invention is to provide methods and apparatus in accordance with the preceding object, wherein an initial beam of charged particles is acted upon by a simple combination of magnetic fields advantageously employed to direct the beam radially into the product all around a circumference thereof. Still further objects of the invention are to provide methods and apparatus of such character, wherein the beam energy is uniformly distributed over a circumference of the product area, where in the intensity of the radiation is uniform about the product, and wherein the size of product that may be irradiated is practically without limit.

Additional objects of the invention are to provide new and improved apparatus for irradiating cylindrical articles, wherein simple, magnetic tools in everyday use are advantageously combined to direct a single beam of charged particles radially into the article all around a circumference of the article, wherein two pairs of magnets are combined so that rotation of one pair effects rotation of 4 the other, and wherein the combined rotational move ment of both causes virtual rotation of the beam about the article to bombard the article radially with charged particles all around a circumferential portion thereof.

The above and other objects may be accomplished in accordance with the invention by projecting a collimated beam of charged particles generally parallel to a tangent to a curved surface to be irradiated and spaced from the curved surface, and bending the beam with a first magnetic field so that the beam follows the curve of the surface. The curved portion of the beam is then bent further by a second magnetic field so that the beam impinges on a portion of the curved surface. The second magnetic field is moved along the curved beam so that the particles therein are continuously directed into the moving second magnetic field and are deflected thereby into all portions of the surface which the curved beam overlies.

Apparatus in accordance with a preferred embodiment of the invention for irradiating a generally cylindrical object includes a first pair of magnets which may be arranged concentrically about the object and spaced apart in opposed parallel relationship. The first magnets produce a uniform magnetic field therebetween which is circumferentially continuous about the object, and which is arranged relative to a beam of charged particles so that the beam enters the field transversely, between the first magnets, and tangentially, beyond the outer surface of the object.

The strength and polarity of this first magnetic field is selected to exert a force on the charged particles which causes the particles in the beam to orbit the object. A second pair of magnets, each of which is carried by one of the first magnetic sources, is arranged to create a second magnetic field along a portion of the orbital path of the particles designed to deflect the orbiting particles radially into the object. Mechanism is provided for rotating the first magnets, thereby to rotate the second magnetic field about the object so that the orbiting particles, directed into the moving second magnetic field, are deflected radially into all portions of the surface which the orbital path overlies.

Other objects, advantages and aspects of the invention .will appear from the following detailed description of a preferred embodiment thereof when taken in conjunction with the appended drawings in which:

FIG. 1 is a diagrammatic illustration of the interaction of an electron with a magnetic field in accordance with an elementary physical principle underlying the invention;

FIG. 2 is a diagrammatic illustration of the interaction of an electron with a magnetic field exemplary of a second and equally elementary physical principle underlying the invention;

FIG. 3 is a perspective view depicting a preferred apparatus embodying the invention in a refined form;

FIG. 4 is an elevational cross section of the preferred embodiment in FIG. 3, taken generally along the center line of the apparatus of FIG. 1;

FIG. 5 is a front elevational view, partly in section, of a specific embodiment illustrating the invention in a broader context;

FIG. 6 is a front elevational view, partly in section, of the apparatus in FIG. 5, exhibiting the effect of displace ment of a magnetic field along a beam of radiation; and

FIG. 7 is a side elevational view, partly in section, of the apparatus depicted in FIGS. 5 and 6, illustrating further the relationship of the magnetic sources, the initial beam of radiation and the article to be irradiated.

As stated at the outset, penetrative radiation has been found to have many applications in industrial processing. Of particular interest in a preferred embodiment of the invention is the irradiation of plastics, such as polyethylene, to improve such characteristics as strength, temperature resistance, and insulating properties of the plastics. The chemical mechanism accomplishing the improvement of such characteristics as .a result of irradiation is a phenomenon termed cross-linking.

Exposure of a plastic material to penetrative radiation causes ejection of an individual hydrogen atom from various carbon chains. The vacated bonds on separate carbon chains subsequently move relative to each other and eventially combine effectively to cross-link the chains. Because of the attendant advantages of crosslinked plastics, such technique has great utility in improving the characteristics of plastic insulation on wires or cables, particularly in the telephone industries where the literally hundreds of thousands of miles of wire manuf actured each day must meet extremely stringent quality requirements.

The problem that immediately arises and one which is well recognized by those skilled in the art, is the difiiculty in irradiating certain troublesome product geometries, such as the cylindrical cross section of a wire or cable. The radiation must uniformly impinge normal to the surface at all points around the circumference thereof in order to obtain optimum depth of penetration and a uniform distribution of beam energy over the product surface. Since such criteria are determinative of irradiation efiiciency, and since the utilization of radiation as a processing tool is still an expensive proposition, the necescity of meeting the above criteria is apparent.

The present invention, in a refined context, is directed to methods and apparatus for irradiating such troublesome product geometries by orbiting charged particles of a collimated beam about the product and directing the orbiting particles radially into such product from all points along the orbit.

The fundamental concepts embodied in the present invention are grounded in two basic principles of physics. Considering the first of these principles with reference to the three dimension-a1 coordinate system in FIG. 1, an electron -e traveling at a velocity v along the X axis perpendicular to a magnetic field having a flux density B along the Z axis, is subjected to a force F in a direction perpendicular to a plane containing the magnetic field and the direction of electron travel, and therefore along the Y axis. This phenomenon is governed by the vectorial equation:

F=-eii x E which, in this special case becomes:

/ F levB/ The second basic principle relied upon, illustrated in FIG. 2, is that an electron -e traveling in the plane of the .X and Y axes with a velocity v perpendicular to a uniform magnetic field which has a flux density B along the Z axis, can be maintained in an orbit defining a circle of radius r if a continuing force F is exerted on the electron by the magnetic field which equals the centrifugal force acting upon the electron in the orbital path. Expressed as an equation, this relationship becomes:

in which in is the realistic mass of the electron because the speed of electrons used for irradiation is significant compared to the speed of light. Since the mass of the electron then becomes the sum of the rest mass and the kinetic energy which equal, respectively, 0.51 m.e.v.s and from 0.5 to 1 m.e.v.-s, the mass will vary between 0.51+O.5=1 and 0.51+1=1.5 m.e.v.s.

Referring now to the preferred embodiment illustrated in FIG. 3, the polyethylene jacket on a cable 11 is to be irradiated, the cable having a generally cylindrical geometry. The cable is axially passed through the central opening 12 in each of a pair of annular permanent magnets 1313 which are spaced apart in opposed, parallel relationship. A hollow, axially elongated, annular envelope 14 is mounted intermedite the annular magnets 1313 so as to permit rotational movement of the magnets relative thereto. The inner and outer walls 15 and 16, respectively, of the envelope 14 are closed at the ends to define a chamber radially coextensive with the annular magnet-s 1313 and the chamber is evacuated to provide a high vacuum therewithin.

The outer wall 16 and the closing ends of envelope 14 are preferably formed of a material suitable to absorb the particular type of radiation employed, yet pervious to magnetic fields, such as glass in the instant case. The outer wall 16 is preferably provided with an integral tube 17 (FIG. 4) extending transversely and tangentially of the envelope 14, and communicating with and interconnecting the evacuated chamber and an electron accelerator 18 to define an evacuated path for a beam 19 of accelerated electrons. The inner wall 15, however, must be formed of a thin foil which is pervious to the radiation because it constitutes an exit window for the radiation. It has been found that foils such as 2 mils of titanium, or 5 mils of aluminum, or 7 mils of stainless steel are transparent to accelerated electrons and yet can withstand the vacuum required.

The permanent magnets 1313 are designed to produce therebetween a uniform magnetic field which is circumferentially continuous about the cable 11 and which permeates the evacuated chamber within the envelope 14. The strength and polarity of the uniform magnetic field are selected to exert a force on the electrons in the beam 19, in accordance with the second physical principle discussed above, which substantially counters the centrifugal force acting upon such particles in a circular orbit concentric within the envelope 14. Since the entire orbital path lies within the magnetic field and since the magnetic field is circumferentially uniform within the glass envelope 14, the electrons in the beam will be deflected into and maintained in the orbital path defined by the envelope 14.

The orbiting electrons are deflected radially into the cable by a second magnetic field created between two permanent magnets 2121 each of which is fixedly incorporated in one of the annular permanent magnets 1313 (as for example in a bore the-rein) in opposed, aligned relationship with the other. The size of the permanent magnets 21 21 is selected so that the magnetic field created therebetween occupies only a small circumferential portion of the chamber defined by the envelope 14. The strength and the polarity of the second magnetic field are selected to exert a force upon the orbiting electrons, in accordance with the first physical principle discussed above, which deflects the orbiting electrons radially into the cable. Hence, the electrons in the beam 18 enter the uniform magnetic field and travel in an orbital path about the cable 11 until they enter the second magnetic field where they are deflected radially into the cable.

A ring gear22 is rigidly mounted about each of the annular permanent magnets 13-13 (FIG. 3) in meshing relationship with a driving gear 23 fixed to a shaft 24 driven at a constant speed in the direction indicated by the arrow A. Rotation of the gears 23 on the shaft 24 causes rotation of the combined magnetic unit (designated generally by the numeral 26 and consisting of the annular permanent magnets 13-13 and the permanent magnets 21-21) about the central axis of the annular magnets in the direction indicated by the arrow B. Rotation of the annular magnets in no way affects the first magnetic field because of the circumferential uniformity and the symmetry thereof.

Rotation of the unit 26 in turn results in rotation of the second magnetic field about the cable along a path substantially coincident with the orbital path of the electrons. As the second magnetic field rotates about the cable, the

electrons follow along therebehind in their orbital path until they enter the moving second magnetic field and are deflected radially into the cable. Therefore, upon rotation of the second magnetic field through one complete revolution, all portions of the cable which the orbital path of the electrons overlies are subjected to radial bombardment by electrons.

In order to effect irradiation of the entire length of cable, the cable may be displaced intermittently or at a constant speed (preferably the latter) longitudinally of the unit 26, in the direction indicated by the arrow C, by any conventional device, such as a capstan. The 1ongitudinal movement of the cable and the constant speed rotational movement of the unit 26 may be coordinated to irradiate overlapping circumferential portions (intended to include axially contiguous circumferential portions as well) of the cable on successive revolutions of the second magnetic field in such a manner that substantially the entire length of cable receives a uniform dose of radiation. In the case of constant speed displacement of the cable, the resulting path of the radially incident radiation relative to the cable defines a helix. Optimum uniformity of dose distribution is achieved in such case by having successive convolutions of the helical path about the cable overlap a substantial amount.

In the specific application contemplated, it is most convenient to irradiate the cable immediately after the polyethylene jacket has been extruded therearound, thereby eliminating the additional handling which would be required in an irradiation operation at a remote location. The openings in the annular magnets 1313 and the envelope 14, are therefore made larger by a substantial degree than the outer dimension of the cable so that no frictional engagement results therebetween.

In the above embodiment, therefore, the present invention advantageously accomplishes virtual rotation of the beam about the cable. The revolution of the magnets 21 and the resultant rotation of the bent portion of the beam, virtually elongates the cross section of the beam while the actual size of the beam remains unchanged and the uniform particle density thereof is maintained. Also, since all particles in the beam are bent through the same angle, beam spreading is uniform. Further, uniform distribution of the incident particles over the product area is effected since all portions around the surface are exposed to all portions of the rotating beam for the same increment of time.

Finally, the intensity of the incident radiation is substantially uniform all around the circumference of the cable. This becomes apparent when it is considered that beam attenuation arises from an interfering media such as the atmosphere. Since substantially all interfering media is evacuated from the envelope, absorption is completely eliminated and the beam intensity is substantially uniform for all orbiting particles deflected into the cable. It is apparent, therefore, that the variations in particle path lengths within the glass envelope is of negligible consequence insofar as it affects beam intensity.

The preferred technique of irradiating troublesome product geometries thus evolved, includes bending the initial beam of radiation with a circumferentially uniform magnetic field so that the particles in the beam orbit the product, deflecting the orbiting particles radially into the product with a second magnetic field disposed along a portion of the orbital path, and moving the second mag netic field along a path substantially coincident with the orbital path so that all portions of the surface which the orbital path overlies may be irradiated.

It is to be noted that a radially uniform and constant first magnetic field may not be desirable; that is, it might be desirable to provide for a certain degree of flexibility with respect to the velocity of the accelerated particles. Particles with varying velocities entering a radially uniform and constant magnetic field designed to orbit particles traveling at a particular velocity, might very well spiral out of the intended orbit. To accommodate such variation in particle velocities, it is suggested that the strength of the magnetic field be increased at progressives ly greater radii. A certain minimum strength may be selected for the inner radius of the magnetic field to orbit particles having a lower limit of the particle velocities, and a certain maximum strength may be selected for the outer radius of the magnetic field to orbit particles hav-. ing an upper limit of the particle velocities, the field strength at intermediate radii being uniformly incremental therebetween. The field strength must, however, be circumferentially uniform and constant at all radii of the field. With such radially increasing magnetic field strength, all particles with velocities between the upper and lower limits will be urged toward an orbital path of a mean radius.

Turning now to a description of the invention in a broader context, the object to be irradiated may have other troublesome geometries, even nonsymmetrical ge-. ometries. The same technique may be employed;.however, in this instance the beam is initially directed along a path substantially conforming to the contour of and spaced from the surface to be irradiated, which path coincides with at least one surface dimension. The beam is deflected from such path in a direction inwardly toward the surface, and the point of deflection is simultaneously caused to move, at least intermittently, along such path so that the beam sweeps over an elongated area along the chosen surface dimension.

Or, the object may have a simple plane surface which is to be irradiated, such as the article 36 in FIGS. 5, 6 and 7. In this embodiment, only a single magnetic field is required and the beam is projected parallel to and spaced from the surface to be irradiated. The magnetic field is produced between a pair of permanent magnets 3131 (FIG. 7) spaced apart in opposed, parallel relationship on opposite sides of an evacuated envelope 32 having an exit window 33 of suitable foil material. The envelope 32, as in the preferred embodiment, communicates with an electron accelerator 34 to provide an evacuated path for a collimated beam 35 of accelerated electrons. The magnets 3131 are mounted at the upper ends of opposite legs of a yoke 36; so as to be disposed on opposite sides of the beam, as shown in FIG, 7, and the yoke is slidably mounted on a pair of guide rods 37-- 37 for movement along the beam longitudinally thereof. This movement may be effected by apparatus such as the cylinder and piston arrangement 38 shown in FIGS. 5 and 6.

The strength and polarity of the magnetic field is selected to exert a force on the electrons in the beam, in accordance with the first relationship disclosed above, to deflect the particles through a prescribed angle of substantial magnitude, preferably toward the surface to be irradiated. Displacement of the yoke 36 in the direction of the arrow D so that the magnetic field traverses the surface of the article 30 at a constant speed (from the left extreme shown in FIG. 5 to the right extreme shown in FIG. 6), effects uniform distribution of the beam energy over the portions of the surface which the beam overlies. Since the beam impinges at right angles to the surface, optimum depth of penetration is also obtained.

In the case of small products to be irradiated, such as that depicted in FIGS. 5-7, the article may be moved transversely of the beam, by a simple mechanical device, so that the entire surface of the object may be irradiated. Uniform distribution of beam energy over the product area may be maintained by coordinating intermittent movement of the product transversely of the initial beam with reciprocal movement of the magnetic field longitudinally along the beam, so that contiguous or overlapping portions of the surface are irradiated on each successive stroke of the field across the surface.

In the case of large products, however, it may be desirable to invert the yoke with respect to FIGS. 5 through 7, so that it lies entirely on the same side of the product as the beam, in which case the movement of a continuous surface may be coordinated with the reciprocal movement of the magnetic field in the above manner to irradiate the entire surface.

Where uniform distribution of beam energy over the product surface is an important factor, the movement of the product in either of the above cases should be intermittent. if uniform distribution is not important, product movement may be continuous. In the latter case, overlapping portions of the product surface will be irradiated on successive strokes of the second magnetic field, and the degree of overlap will vary within each stroke.

The unique result obtained by all the above techniques is that the area of a collimated beam of radiation may be virtually elongated substantially without limit by bending the beam with a magnetic field and moving the magnetic field longitudinally along the beam. The beam may be virtually enlarged to encompass an entire surface of the article by coordinating intermittent or continuous longitudinal movement of the article with movement of a magnetic field.

While a preferred embodiment is described in detail hereinabove and a more general description is provided of the invention in a broader context, various modifications may be made without departing from the spirit and scope of the invention and it is intended that all such modifications be interpreted as contemplated by the invention.

What is claimed is: -1. A method of extending at least one dimension of the effective cross section of a collimated beam of charged particles, which comprises the steps of:

bending the beam through a prescribed angle of substantial magnitude relative to the initial path of the beam by arranging a magnetic field in said path; and

moving the magnetic field along the initial path of the beam longitudinally thereof to cause the bent portion of the beam to sweep over an elongated area.

2. A method of irradiating portions of a surface of an article, which comprises the steps of:

projecting a collimated beam of charged particles generally parallel to and spaced from the surface to be irradiated;

bending the beam by arranging a magnetic field in the path thereof, through -a prescribed angle relative to the initial path of the beam and toward said surface so that the bent portion of the beam impinges on a portion of said surface; and

moving the magnetic field along the initial path of the beam longitudinally thereof, to cause the bent portion of the beam to traverse at least one dimension of said surface.

3. A method of irradiating portions of a surface of an article, which comprises the steps of:

projecting a collimated beam of charged particles generally parallel to and spaced from the surface to be irradiated;

bending the beam by arranging a magnetic field in the path thereof, through a prescribed angle relative to the initial path of the beam and toward said surface so that the bent portion of the beam impinges on a portion of said surface;

moving the article parallel to said surface thereof and transversely of the initial path of the beam; and moving the magnetic field along the initial beam longitudinally thereof;

whereby at least two dimensions of said surface may be traversed by the bent portion of the beam.

4. A method of irradiating a prescribed surface area of an article, which comprises the steps of:

projecting a collimated beam of charged particles generally parallel to and spaced from the surface area to be irradiated;

bending the beam by arranging a magnetic field in the path thereof, through a prescribed angle relative to the initial path of the beam and toward said surface area so that the bent portion of the beam impinges on a portion of said surface;

moving the article to cause the bent portion of the beam to trace a first path over the prescribed surface area;

moving the magnetic field along the initial path of the lbeam longitudinally thereof to cause the bent portion to trace a second path over the prescribed surface area generally perpendicular to the first path; and

coordinating the movements of the article and of the magnetic field so that the movement of one is reciprocal across the corresponding dimension of the prescribed surface area at a rapid rate relative to the movement of the other, whereby the entire prescribed area may be irradiated.

5. A method of irradiating a prescribed surface area of an article, which comprises the steps of:

projecting a collimated beam of accelerated electrons generally parallel to and spaced from the surface area to be irradiated; bending the beam by arranging a magnetic field in the path thereof, through an angle of substantially relative to the initial path of the beam and toward said surface area so that the bent portion impinges on a portion of said surface; moving the article generally parallel to said surface area thereof and transverse to the initial beam; and

reciprocably moving the magnetic field along the initial path of the beam longitudinally thereof to traverse said surface area, the reciprocal movement of the magnetic field being coordinated with the movement of the article so that successive portions of the prescribed surface area may be irradiated in turn on successive strokes of the magnetic field, whereby the entire prescribed surface area of the article may be irradiated. 6. A method of irradiating objects of complex shape and objects having large surface areas, with a single collimated electron beam, without appreciably affecting the initially established particle density distribution across the cross-section of the collimated beam, which comprises the steps of:

forming and collimating a high energy electron beam; directing the collimated beam along an initially established path closely adjacent to at least one surface dimension of an article to be irradiated; and

deflecting the beam at a substantial angle in a direction inwardly toward the article to be irradiated by moving a magnetic field through at least a plurality of points in succession along at least a portion of the initially established path, thereby causing the beam to irradiate at least a portion of the article surface along the chosen dimension thereof.

7. Apparatus for deflecting charged particles in a collimated beam into an orbital path about an object and for deflecting the orbiting particles into the portions of the object which the orbital path overlies, which comprises:

first magnetic means rotatable about its polar axis for producing a fixed, continuous and uniform magnetic field about the object;

means for producing a collimated beam of charged partioles directed into the first magnetic field transversely thereof and outwardly of the periphery of the object, the strength and polarity of the first magnetic field being selected to exert a force on the charged particles which substantially counters the centrifugal force acting upon such particles in following a circumferential path about said axis of the object, so that the particles may orbit the object with said axis defining the center of rotation;

second magnetic means carried by said first magnetic means at substantially the radius of the orbital path of the charged particles, for producing within the first magnetic field a second magnetic field having a 1 1 strength and polarity selected to deflect the particles from their orbital path and into the object; and means for rotating said firs-t magnetic means about said axis, thereby to rotate the second magnetic field about said axis along a path generally coincident with the orbital path of the particles;

whereby the orbiting particles are deflected into all portions of the object which the orbital path of the particles overlies.

8. The apparatus as recited in claim 7, wherein: an evacuated envelope is disposed within the magnetic field produced by the first magnetic means and is continuous about the object, to enclose the initial beam pathand the orbital path of the charged particles and to provide a low density medium of travel therefor so that beam intensity may be substantially uniform all about the object regardless of unequal distances of particle travel, said evacuated envelope being substantially transparent to the magnetic fields.

9. Apparatus for irradiating a generally cylindrical object so that the radiation penetrates the outer surface of the object radially at all points around a circumference thereof;

a pair of annular magnets axially spaced apart in opposed, parallel relationship and arranged to permit the object to pass axially therethrough, said annular magnets producing a magnetic field therebetween which is circumferentially continuous and uniform about such objects;

means for producing a collimated beam of charged particles directed into the first magnetic field transversely and tangentially thereof at a radius beyond the outer surface of the object, the strength and polarity of the first magnetic field being selected to exert a force on the charged particles which substantially counters a centrifugal force acting upon such particles in following a circumferential path about the object so that the particles may orbit the object;

a second pair of magnets, each fixedly incorporated;

in a portion of one of said annular magnets at substantially the radius of the orbital path of the particles, said second pair of magnets being aligned parallel to the axis of said annular magnets; said second magnets producing a magnetic field thereb-etween having a strength and polarity selected to 12 exert a force on the orbiting particles which deflects them from their orbital path radially into the object so as to penetrate the portions of the surface thereof which the intersection of the orbital path and the second magnetic field overlies; and

' means for rotating said annular magnets in synchronism about the axis thereof, thereby to rotate the second magnetic field about the object along a path generally coincident with the orbital path of the particles;

whereby the charged particles are deflected by the second magnetic field radially into all portions of the core which the orbital path of the particles overlies.

10. The apparatus as recited in claim 9, wherein:

the annular magnets comprise a pair of annular permanent magnets;

an evacuated envelope having a central opening therethrough is interposed between said annular permanent magnets with the central openings therein communicating with the central opening in said envelope, said envelope having inner and outer walls which are closed at the ends and an integral tube communicating with and connected to the beamproducing source to enclose completely the path of the initial collimated beam and the orbital path of the charged particles in a vacuum, the inner wall of said envelope being substantially transparent to the charged particles, and the outer wall and closing ends being substantially transparent to the magnetic fields; and

the second pair of magnets are permanent magnets.

References Cited by the Examiner UNITED STATES PATENTS 2,741,704 4/1956 Trump et a1 25049.5 2,858,441 10/1958 Gale 250-495 2,897,365 7/1959 Dewey et a1 250-495 3,010,018 11/1961 Zitfer 25052 3,104,321 9/1963 Smith 25049.5 3,109,931 11/1963 Knowlton et a1 25049.5

FOREIGN PATENTS 789,456 1/ 1958 Great Britain.

RALPH G. NILSON, Primary Examiner.

Claims (2)

1. A METHOD OF EXTENDING AT LEAST ONE DIMENSION OF THE EFFECTIVE CROSS SECTION OF A COLLIMATED BEAM OF CHARGED PARTICLES, WHICH COMPRISES THE STEPS OF: BENDING THE BEAM THROUGH A PRESCRIBED ANGLE OF SUBSTANTIAL MAGNITUDE RELATIVE TO THE INITIAL PATH OF THE BEAM BY ARRANGING A MAGNETIC FIELD IN SAID PATH; AND MOVING THE MAGNETIC FIELD ALONG THE INITIAL PATH OF THE BEAM LONGITUDINALLY THEREOF TO CAUSE THE BENT PORTION OF THE BEAM TO SWEEP OVER AN ELONGATED AREA.

7. APPARATUS FOR DEFLECTING CHARGED PARTICLES IN A COLLIMATED BEAM INTO AN ORBITAL PATH ABOUT AN OBJECT AND FOR DEFLECTING THE ORBITING PARTICLES INTO THE PORTIONS OF THE OBJECT WHICH THE ORBITAL PATH OVERLIES, WHICH COMPRISES: FIRST MAGNETIC MEANS ROTATABLE ABOUT ITS POLAR AXIS FOR PRODUCING A FIXED, CONTINUOUS AND UNIFORM MAGNETIC FIELD ABOUT THE OBJECT; MEANS FOR PRODUCING A COLLIMATED BEAM OF CHARGED PARTICLES DIRECTED INTO THE FIRST MAGNETIC FIELD TRANSVERSELY THEREOF AND OUTWARDLY OF THE PERIPHERY OF THE OBJECT, THE STRENGTH AND POLARITY OF THE FIRST MAGNETIC FIELD BEING SELECTED TO EXERT A FORCE ON THE CHARGED

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