US2670443A - Radiation beam forming unit - Google Patents

Description

Feb. 23, 1954 J. c, PENNOCK ETAL 2,670,443

RADIATION BEAM FORMING UNIT 5 Sheets-Sheet 1 Filed Feb. 28, 1951 [72 van Z07 c 72 6. Pennaciv, A Zerz Tffiaccizz'erz',

Feb. 23, 1954 J. c. PENNOCK ETAL V 2,670,443

RADIATION BEAM FORMING UNIT Filed Feb. 28, 1951 5 Sheets-Sheet 2 I /08 -iiizli- /00 .04 90 Jul/e72 tans 1954 J. c. PENNOCK ETAL 2,670,443

RADIATION BEAM FORMING UNIT Filed Feb. 28, 1951 5 Sheets-Sheet 5 Inventors.- Joizn C. Pennociz',

A Zerz J. Bacck z'erz',

as 2%" 84 3y A zgy.

Feb. 23, 1954 c, PENNOCK ET AL 2,670,443

RADIATION BEAM FORMING UNIT Filed Feb. 28, 1951 5 Sheets-Sheet 4 4M1. QM

At y.

5 Sheets-Sheet 5 Znven tom: 6 Pen nae/1' III II/ I I "a" J. C. PENNOCK ET AL RADIATION BEAM FORMING UNIT Joim A Zert Jfiacckz'erz', y fl4v M Feb. 23, 1954 Filed Feb. 28, 1951 Patented Feb. 23, 1954 UNITED STATES 'ren'r OFFEQE:

RADIATIQN? BEAM EQRMING UNIE.

sachusetts ApplicationFebruany 28, 1951;, Serial Nni 213,174

11 Claims, (01. 250-105) This. invention relates. to devices for forming abeam of radiant energy which. may be used for the treatment. of disease or. the. radiography of structural, materials or. the. like. More..p.articularly. the. invention is. concerned. witha new and improved radiant energy beam-forming. device in which aradioaotivesource isremovably mounted ina shield of radiationabsorbr'ng material with provision for, producing an. opening in. the ab.- sorbing material to form a collimatedbeam of radiations and. embodying new and improved meanspermitting the simple andsaie. loading into the shieldv and unloading. therefrom. oi the radio.- active source, together with a novel fail safe. arrangement, to keep the, source, shielded, in the event. of power failure. to the device.

Devices for. the. purpose stated. abovehave. been usedifior a number ofv years with. radium. as. the sourceof' radiation. Because of the great cost of such. material and the. inherent limitation on the amountoiradiation which. can be obtained; from a naturally radioactive source of givensi'ze (volume specific, activity).,, such devices have never been built to handle more than about 50 grams of radium.

Beam. forming, devices usingradium sources of 1 to 20. grams have usually consisted of a pneumatic device for transporting the radium source froma shielded storage containen which protects the attendant personnel from irradiation, to a collimating device and then back to the shielded.

storage, container. While such a pneumatic transport system is satisfactory for handling radi'ation sources of limited strength, the possibility of'sticking of the'radiation source in the transport tube in a positionin which there is no protection for the attendant personnel. makes sucha device extremely hazardous foruse with very high intensity gamma-ray-sources.

In order to arrive at; some estimate of the; potential danger inherent in the use" of" very high intensity gamma-ray sources, a comparison is given of the time required to receive a meanl'ethal d'ose (assumed to be 250 roentgens over'the whol'ebody) ofgamma-radiation from a 50 gram radium source, and from a 1000 curie and a 3:0;00'0" curie cobalt-60 source if" the entire body is exposed at a distanceoi" one meter from the source.

' Lethal exposure table Source Timex Required 50 Gram Radium. 1,0011, Curio: Cobalt-5 10,000., Curie Cobalt-.60 w,

It becomesobvi'ous from thevabove that the degreeto which the device in which the source will be used must be made fail-proof increases very rapidly with the intensity of the source to be used.

Very high intensity. gamma-ray sourcesare now available and. will become increasingly available in the form of materi'alsrwhich have been made artificially radioactiveby exposure to neutrons in a nuclear reactor; Such materials can be made with a much higher rate of emission of radiant energy per unit volume of source (higher. specific activity) than is. possible with radium. or other naturally radioactive materials and at a much lower cost per unit of radiant energy. Itis, therefore, now possible and economically practical to produce and use radiation sources with gammaray emission equivalent to thousands of grams ofradium;

Several mechanisms which may be used to form collimated' beams of radiations by moving a radioactive source into position in line with a hole in surrounding radiation absorbing mate rial have-been suggested. All ofthe devices which have been suggested have three major disadvantages: First, they require power of some sort to move the source from the beam-forming to the completely surrounded" position and the hazard of having the source in the beam-forming position for longer than is safe if the power supply fails is always present second, it is extremely difficult to-produce a mechanism which will: always position the source in exactly the. same. location for forming the beam. and arry'location difference will change the shape of the gamma ray beam emergingfrom the device; and third, the problems of protection of personnel: during the loading of theradioacirlve source: into a device which requires: that the radioactive. source must. subsequently move: during. the operation of the device are much more difficult of solutionthan the similar problems-with a deviceiinrwhichthe source remains; fixed after it. has been loaded into the device.

The invention has for its primary object the overcoming oi the foregoing; difficulties by providing; adeviceiorforming a collimated. beam of penetrative radiations which will close ofii the beam automatically in. case of; failure of the supply ofipower'tothe device and which makes. provision for the easy loading into. and unloading from thesurrounding absorption material of the radioactive. source.

A further object of the invention is to; provide a devices-of theforegoing class: inwhichthe radioactive source is stationary durin v operation; Withtthe -foregoing objects in mind, theinvention is featured by the provision of a shielded container adapted to be loaded with and thereafter to hold an extremely intense radioactive source in a fixed position generally at its center, the shield being composed of radiation absorbin material of sufficient thickness to reduce the radiation intensity at or near its surface to a tolerable level and having a collimating slot extending from the location of said source to its surface for forming a beam of radiations, the shield also having a slot intersecting the collimating slot and adapted to receive a shutter of radiation absorbing material, the shutter being so mounted and arranged that, in the event of power failure, it will be moved by the force of gravity alone to its closed position, blocking said collimating slot, even in a wide variety of different positions of the container, the collimating slot also being preferably provided with an iris for adjusting the crosssectional area of the beam of radiations.

The novel radioactive source holder, shielding carrying container therefor and the special arrangement for loading of the source into the radiography container have been made the subject matter of a separate divisional application co-pending herewith.

Still another object of the invention is to provide a radiation beam-forming unit having a gravity operated shutter for closing off the beam and which will permit the proper functioning of such shutter in a variety of different positions of the device.

Still a further object of the invention is to provide a device of the character described which may be loaded with a radioactive source or unloaded without danger to the operatin personnel.

With the foregoing objects, features and advantages in view, the invention consists of the novel features, combinations and arrangement of parts as disclosed in the following detailed description taken in connection with the accompanying drawings which disclose a preferred embodiment thereof and in which like numerals refer to like parts in the several views.

Fig. 1 is a front view of the outside of the beam forming unit;

Fig. 2 is a side view of the same;

Fig. 3 is a bottom view of the unit which shows only the face of the iris;

Fig. 4 is a section with portions cut-away on line 4-4 of Fig. 1 showing the shielding sphere shutter, shutter supports, shutter operating mechanism, and the iris;

Fig. 5 is a section with portions cut-away on line 55 of Fig. 4 showing further details of the shutter, shutter supports, shielding sphere, and source cylinder;

Fig. 6 is a fragmentary sectional view on line 66 of Fig. 4 showing the details of the movable mounting for the shutter supports on the shielding sphere;

Fig. 7 is a fragmentary section on line 1-1 of Figs. 2 and 4 showing the movable mounting of the iris on the shielding sphere;

Fig. 8 is a fragmentary sectional view taken on line 8-8 of Fig. 7 showing further details of the mounting of the iris;

Fig. 9 is a sectional view on line 99 of Fig. 7 showing further detail of the movable mounting of the iris;

Fig. 10 is a view taken on line id-IO of Figs. 2 and 4 showing the iris;

' Fig. 11 is a partially diagrammatic view of one of the block guides of the iris, including the supports for the cable rollers;

Fig. 12 is a schematic diagram showing the arrangement of the cables used to move the absorbing blocks in the iris;

Fig. 13 is an elevation with portions cut-away of the source holder; and

Fig. 14 is a fragmentary representation illustrating the manner of loading the source cylinder into the shielding sphere.

In the preferred embodiment here disclosed, the device consists of a shielding sphere 22 in which is mounted a shutter 29 which is movably connected to the shielding sphere 22 through the shutter support arm 24, the shutter support bear ings 26, and the shutter support tracks 28. Said shutter 20 may be made to move linearly between the closed position in which it is shown in Fig. 2 and the open position in which it is shown in Figs. 4 and 5 by means of a solenoid 30 or other device for producing linear motion. The solenoid 3') acts through the solenoid core fork 32, shutter lever 34, fulcrum fork 36, and shutter support fork 38 to move the shutter 26. The motion of the shutter 20 to open position is just sufficient that the collimating opening 49 is square in cross-section in a plane perpendicular to the vertical center line of the device. When the solenoid is not activated, the shutter 20 moves to closed position automatically; when the solenoid 30 is activated by passing an electric current from a power source (not shown) through the wires 42 and thence through the solenoid 38, the shutter 20 is drawn into the open position. The shutter 28 is so mounted that the force of gravity always acts in the direction of moving the shutter 20 to the closed position as will be described below in the description of the shutter mounting. Thus the shutter 20 is always in the closed position except when power is applied to the solenoid 30.

The shielding sphere 22 is constructed of a strong material which also has the property of strongly absorbing radiations emanating from the source used, in this case gamma rays. Such a material as tungsten or an alloy containing a high percentage of tungsten is suitable. The shielding sphere 22 may also be constructed of a sturdy shell which need not have the additional property of strongly absorbing gamma rays but which is filled with another material which has the property of strongly absorbing gamma rays. Such a combination of material as a steel shell filled with lead is suitable.

A slot 44 formed in the shielding sphere 22 provides room for the insertion of the shutter .20 and also forms three of the walls of the collimating opening it! which is produced when the shutter 26 is in the open position. The side of the slot 44 which is at the top in Fig. 4 is formed at an angle to a line perpendicular to the vertical center line of the device. This angle is approximately 20 degrees in the preferred form of the invention but may be slightly more or lesswithout affecting proper functioning. The slot 44 extends beyond the vertical center for a distance equal to one-half its own width.

The shutter 20, like the shielding sphere 22, is constructed of a strong material which also has the property of strongly absorbing gamma rays. Again like the shielding sphere 22, the shutter 20 may be constructed of a shell of a strong material which need not have the addi:

but which is filled with another material having good. absorption characteristics. It is not necessary to. the. invention that" the; same material or combination of: materials bev used in: the shutter 29 aslis used. in: the: shielding: sphere 22:

The shutterifl. so. shaped. that it. fit's closely into the slot 4 3 in the: shielding sphere 221 with only sufiicient clearance between the walls-oi; the shutter'lflland theslot' it to: allow linear motion of, thexshutter 20 with: respect" to theslott M inv a direction parallel: to the.- side'. of. the slot. M which isat thetop; in Fig: ll Furthenthe shutter'20 is oh sufiicient: height and length. that when. it is in the; closed position as-shcwnv in Fig; 2, it mates with: the. slot: 44. at.- both the top. and bottom in such. a:. way that: the radioactive source 45: is shielded. on all sides by. sufiicient thickness of gamma ray absorbing material to. reduce the. radiation intensity at: or' near. the surface. of the Shutter; 26. to; aztolerable: leveli. Further, thershutten 20. is so shaped that when it isin the: open position asshown in Fig. 4* the verticalinside wall of." the shutter. 2B extendsisufliciently far along a line parallel to the vertical center. line of the device: so. that:the bottom of. all of" the four. vertical; walls of the collimating opening 461' are in the-same: plane. said. plane being taken perpenidicularsto vertical center. lineof the device.

The; shutter 20 is. movably mounted on. the shielding sphere; 22- through the shutter support arm 24 the shutter: adjustment screws 43, the shutterradiustment pivots 52 the shutter adjustment arms 50; the shutter" support bearings 2-5, and: theshutter support tracks 28.. The; shutter support: arm 24. is a rigidmember whicha firmly fastened to the. shutter 23: through. the: shutter support plates 5.61 and: shutter support ribs 56 which are; or course, firmly: fastened to both. the shutter: 20 and the shutter: support arm 24.. The shutter. support arm 24. extends: around the outsideof. the. shielding: spherezz'. The shutteredjustment arms 59 are. mounted on the shutter support arm. as by't'hev shutter adjustmentpivots 52 around which said shutter adjustmentarms B are. free. to' rotate. The shutter" support. bearings 26- are mounted? on; the shutter" adjustment: arms 50: by; the"v shutter support bearing pins: 58 around WhichLsaid shutter supportzbearings 25.:arefree to rotate. Eight of the shutter support bearings- 2B have their axes of. rotationon: aline perpendicular: to the: plane: indicated by' line 4'-4: and. four oftheshutter-supportibearings 25: have their axis of: rotation on a. line: perpendicular to the plane indicated by linen-5 Theshutter support'bean ings Zfizroll on. the surfaces. cit-the shutter-support tracks". 28. The shutter adjustment screws? 4'8 pass" through internally threaded apertures in theshutter support-arm 245 and the-ends of? said shutter adjustment. screws 4%? bear on the. end. of the. shutter adjustment: arms 59 opposite to the end where the shutter adjustment pivots 52 are located. The shutter adjustment screws 43 may be; moved linearly along their'axes in the normal fashion of a screw and'will then bear down on the-shutter-adjustment arms 51! causing-thezshum t'ersupporl'i bearings 26 to. press against theshuttensupport-trackeztl By-Tepeated: successive ad'- justments of the shutter adjustment screws 45 the-shutter may beraised or lowered, moved from sideto side, and turned slightly about both a ver tical and a. horizontal axis to permit the exact positioning of the shutter 28 within the slot 45 so that said shutter z'll will be freeto move linearly-within said'slot 4'4 and parallel to the walls off said" slot; 44'; I

'- The shutter supporttracks" 28 are made of astrong: hard-material such; as: steel; are firmly attached to:- the: outside. of the; shielding sphere 22 anda'are: given: support by" shutter support. tracks ribs Gllfsuch as are-shown in Figs; 4,. 5. The. horizontalsurfaces of the shutter support tracks28 are smooth and are made parallel to the side. of the slot 44. which is, at the top in Fig. 46 Theouter vertical surfaces of'the shutter support tracks 28' aresmooth and are made. to be parallel tot-he plane indicated by line 4-4 for at least a distance equal to the length of travel of the shutter 20.. The shutter support tracks 28 thus form surfaces onwhich the shutter support bearings 2E ride to support the shutter 20 and to define the direction of. travel of the shutter 20 so that: it" moves freely and without binding within the confines of the. slot. 4.4.,

The shutter support, fork 38 is'firmly attached to the. shutter support plate. 54; the fulcrumfork 35 isfirmly' attachedto the solenoid base 62; the solenoid; core fork 32; is firmly attached; to: the solenoid core fit; The shutter lever 34 is a strong, rigid: member which. is re tatably attached to the ful'crumicrl; 35=by the fulcrum fork pinfifi which passes through round holes in the fulcrum fork 36 and the shutter lever 34'. The shutter lever is attachedin a similar manner to the solenoid core ierk: and the shutter support fork 38 except that at these places a slot is. provided. in the shutter lever 34 in place of; the round hole inorder to. permit the required motionwhen the. shutter 2d is moved from the; open to the closed positionor fIOmithG. closed to theopen position.

The solenoid base. 82 is. a cylindrical section which is firmlyrattachedtoithe. shielding sphere 22. At least enough of the solenoid base. 62 is made of a gamma ray'absorbing material insuch a shape" that the. gamma. rays from the radio;- active source mustpa'ss throughsufiicient thick:- ness of. absorbing material to' reduce; the radia. tion intensity at or near: the surface of the solenoid' cover 68. to a. tolerable. level. In the embcdime-nt'shown in the accompanying drawings. thesolenoi'dfbase i fiiista-cylin'der of the same-.material or. combination. of materials, as the shielding sphere 22:. The invention. is not changed, however, if. thesolenoid base. is a. hollow cylindrical; sectionin the: natureof a. cover: and containingz only sufficient. absorbing material. that the. gamma. rays from; the; radioactive source 46 must passv through. at: least as. much absorbing material? before reaching the surface in: this. direction; as they would if they passed through. the. shielding; sphere 22. in any other direction and containing further: such. solid pieces as. may be required. to permit: the. fastening: of the solenoid 392 or equivalent onto the shielding sphere 22"..

The solenoid: cover 53 is a. hollow piece which is removably mounted. onto the solenoid base 62 and covers solenoid. 3t. and whichv contains an opening through. which the solenoid core 54': and the; solenoid core fork 32'. pass. Said. solencidv cnver serves the usual functionsof a cover such protection from dust and damage by" knocking and may he made of any: suitable material.

The axle in is a hollow shaft passingthrough firmly attached! to: the shielding sphere 22 and; pretruding from. .hersi'd'es cf'said. shielding 22-;to1iormstrunnionsby which the entire device may: be supporteda The axle 1.0 is pan-- tially' cut. away at and. near the. center of the shielding sphere where the axle passes tlinzougn the: slot #15: in. orderto permit the smitten 20 to slide into the slot 44 and in order to eliminate partial absorption of the gamma radiation from the radioactive source 46 which would occur if the rays were required to pass through the full wall of the axle ii The axle ill per forms the dual function of providing a means of supporting the entire device and of providin an opening for the insertion of the radioactive source 44 Contained in the source cylinder 12.

The hangers it which support the device may be of any type which will not permit lateral motion of the device with respect to the hangers I4 but which will permit rotational motion of the device about the axle It. The hangers T l may ce attached to any solid foundation such as the ceiling, walls, or floor of a room. These hangers may be so arranged that translational motion of the device can be produced in any direction.

Since the device may be rotated about the axle i0, it is necessary to indicate how the shutter 20 will operate when the device is at any angular position other than the vertical position shown in the drawings. The device may be operated with gravity closure of the shutter 29 between the two positions at which the component of the force of gravity which acts in the direction of closing the shutter 2G is just sufficient to overcome the opposing frictional forces and cause the shutter 20 to close. Thus, one extreme position is with the gamma ray beam pointing in a generally downward direction with the shutter support tracks 28 in a nearly horizontal position but sloping downward slightly to the right as seen in a view taken on line 4-4; the other extreme position is with the gamma ray beam pointing in a generally upward direction with the shutter support tracks 28 in a nearly horizontal position but sloping slightly downward to the left as seen in a view taken on line fi--5; and all positions produced by rotation of the device from position one clockwise to position two are permissible. It may be seen by examination of the drawings (particularly Fig. 4) that a component of gravitational force is acting in the direction of closing the shutter in any of the above-defined permissible positions.

Referring to Fig. 13, the source cylinder i2 is a thin-Walled cylinder with an outside diameter nearly equal to the inside diameter or" the axle '10 but sufiiciently smaller to permit the source cylinder i2 to slide freely within the axle ill. Said source cylinder 12 is made of a material of sufficient strength and hardness to support its contents and to permit it to slide within the axle 19 without binding. The radioactive source is a capsule which fits inside the source cylinder l2 and which contains the radioactive material which is used as a source of the gamma rays which form the gamma ray beam. Said radioactive source 46 is positioned in the center of the source cylinder 72 between the two source cylinder plugs 18. The source cylinder plugs F6 are made of a material which has the property of strongly absorbing gamma rays, are fitted close- 1y to the inside diameter of the source cylinder 12, and serve the purpose of preventing unwanted beams of gamma rays from coming out of the ends of the axle l8.

The manner of loading the radioactive source 46 into the shielding sphere 22 is indicated in Fig. 14. The radioactive source 46 and the source cylinder plugs 16 have previously been loaded into the source cylinder 72 in a working area provided with the necessary safeguards and equipment. The source cylinder 12 is then transported to the beam forming unit in the auxiliary shielding container 18. The auxiliary shielding container 13 is made of a material which has the property of strongly absorbing gamma rays or of a shell of a strong material such as steel which is filled with another material which has the property of strongly absorbing gamma rays.

Said auxiliary shielding container 18 may have any convenient shape provided only that it provide sufiicient thickness of absorbing material to reduce the intensity of radiation outside it to a tolerably low level and that it contain a cylindrical hole of the same dimension as the inside dimension of the axle 1E5, said hole to contain the source cylinder 12 during transport. In order to load the radioactive source 46 into the beam forming unit, the hole in the axle 40 is aligned with the hole in the auxiliary shielding container 18 which contains the source cylinder 12 and the latter is pushed out of the hole in the auxiliary shielding container 18 and into the hole in the axle 10 using a ram 80. Thus, the radioactive source 46 is always surrounded by suflicient absorbing material to reduce the radiation intensity to a level which is tolerable to the people near it except for the moment when it is actually being loaded into the beam forming unit. If desired, it is possible to provide additional gamma ray absorbing material surrounding the space between the beam forming unit and the auxiliary shielding container 18 to reduce the radiation intensity in the surrounding area during the moment of loading. Even if no such additional protection is provided, however, the persons who are doing the loading are to a great extent protected by interposing the auxiliary shielding container it between their persons and the radioactive source 46 during the moment of loading. If it is desired to remove the radioactive source 48 for replacement or to make the maintenance of the beam forming unit easier, the above procedure is reversed and the radioactive source 46 is pushed from the beam forming unit into the hole in the auxiliary shielding container 18.

The iris B2 and the manner of its attachment to the shielding sphere 22 will now be described.

On the bottom of the shielding sphere 22 and firmly attached to or forming a continuous part of the same is a cylindrical annulus which will be designated as the scatter shield upper section 84. This section 84 is constructed of a strong material which also has the property of strongly absorbing gamma rays. It may be constructed of a shell of a strong material which need not have the added property of strongly absorbing gamma rays but which is filled with another material which has the property of strongly absorbing gamma rays. In conjunction with the iris scatter shield 86 and the upper absorbing blocks 88 and lower absorbing blocks 90, the scatter shield upper section 84 surrounds the path of the gamma ray beam between the bottom end of collimating opening 40 and the bottom end of the iris 82 and reduces the amount of gamma radiation which passes out of the iris in any direction other than the direction of the original beam. The iris 82 is best described by referring to Figs. 3, 4, 10, 11 and 12 and its movable attachment to the shielding sphere 22 is best described by referring to Figs. 4, '7, 8 and 9. The iris 82 consists of the upper absorbing blocks 88, the lower absorbing blocks 90, and guides for the same, and means for moving the blocks "of each pair toward and away from each-other. The

functioncf the iris 82 is 'tocQllima-te the gamma ray beam :further afterit passes outof t e-ooh limating opening '48 and to wars; the 75126 and cross-sectional shape of the :beam'by Dnsitiening absorbing blocks in sucha way thatfthey absorb part of the; radiations, and to; reduce theamount of gamma radiation which passcs cutof;the;iris in any direction other thanit-he direction of the original :bearn.

Referring :now to Figs. '4 and .510, iitrnay be seen that the two sets of absorbing blocks 1st and 90 are movably mountedinthe iris :Qnesse above the 'other'and with the; directionof motion of the two :sets :cf blocksgmutuallyperpendicular as seen in :Fig. .10 andperpendicularvto the-Nev tical center line "of -.the device. IIhe blocks are composed vof material having the-desired radiation absorption characteristics. :In:addition,.the blocks may have a piece inserted .along their edges nearest the .vertical :center .line. of -:;the device,.said piece being readeof a material ;which has the property of absorbing gammaraysexccptionally strong. This inserted piece .wculdserve the function of absorbing :very stronglylthe edge of thexgaininaray beam as it'passes thronghthe iris and thus of producing gamma ray beam with very sharply defined edges.

The means for moving :the two sets of absorbing bloclts 8t and til will now be described. Fig. 12 shows a schematic diagramcf thearrahg-ement for producing motion of one set ofsaosorhing blocks, that of the :otherset :heingidenticai except for direction :of rrnotion.

In order to ."produce -agamma ray beam the center of which is alwayscoincident withthe vertical centeriline of the device, it is "desirable to use'a means of adjusting the distance of separation of the two absorbing blocks in each :pair of blocks, such thatboth vblocks inieach pair are not only moved by the adjustment of .a single control, but that they will be moved-toward or away from each other the same distance by ad justnient oi that control.

For convenience in. describing the -meanest producing the motion of the blocks, Fig. 12 will be taken to represent the lower absorbing-blocks 96, but in actuality it could betalren 'to represent the upper absorbing blocks 88 as well. a An iris'control screwt2 is rrotatably mounted in the iriscover -94. Motion of thesirisgcontrol.

direction along the axis .of the iris control screw.

The blocks 90 are interconnected :by iaz'pai-ruof cables. I 0.2 which :make .the absorbingblocker/nichis not attached tothe iriscontrolgdrive bracket perform the desired -motion. Referring ;to ;li i g. 12, .it will be seen that .whenthc o yrol knob 96 turned to move the bracket "l begin";

wardly' r outwardly the ,two blocks -moye toward or awayfrom each Other, 1 equal distance.

.A similar cable system H14 operates ,the other set of blocks 88 under the controlof theiknobslilii. .The absorbing blocks aremounted .between block-guides 108 ,of the type indicatedgin the schematic .view of Fig. 11 so that only.,1ine.ar

motion .in the desired direction '.is .proiiuced 139 the action of the iris control knob and; the associated motion producing equipment.

The iris 82 is rotatably andremovably-meunted on the shielding sphere 22 through the iris support sill, the outer iris ring Hi2, the irissupport wheels H4, and the his support track lit. -The irissupport track Hi5 is firmly attached to the scatter shield upper sectiont. The iris-support wheels ilt ride on the surfaces of ii-shaped notch icut in the outer surface or theirissupport iris suppor:t wheels H4 through theiris support wheel mounts Ht which are adjustable inp siticn tcpermit the iris support wheels. H4 tobe so located that they will ride accurately on the surfaces of the notch in the iris support tracl; ILG. ltvmaybe seen that the outeriris ring-H 2 is thus rotatably attached to the scatter shield upper section {it regardless of the position of the a device.

mount E22. by a-pin lidwhich rideswithina slot intheiris support tit. Rotationof;theiris support knob, 1-26 causes the irissupport; i, ii} tamevc in and out o-f the irissupportmount 122. Three riszsusnorts .ii ea xi t e asso at d moun in are arranged equidistant around the circumierence ofthe iris82 and-maybe aligned with three equally spaced apertures in the outer iris ring H2. When so arranged, theiris supports tit may be moved i to th ap tur i h ou iris :ring 112 by turning theiris support .knobs tzdand-the iris 82 thus be attached to theouteri iris ring H2. The iris 182 may be removedby reversingthe above process. A slot is provided in rthe outer iris ring H2 as indicatedin l 'igs. 7 andQ to facilitate the alignment of the iris supports 1 ill and the apertures in the outer iris ring I I2. I

, The-device oi the invention has been illustrated as adapted for use with a strong emitter of gamma rays, such as cobalt-60, since ior therapeutic and radiographical purposes ,such radiation, at present, appears to. have the greatestpractical value. ever, that modifications and "changes, primarily as to the nature of the absorbing material .employed in the shielding members, will be readily apparent tothose skilled in the art to adapt the unit for use with other radioactive sources emitting predominantly other types of penetrative radiations. For example, sources ofneutrons might be employed necessitating the employment of parafiin or othermaterial of like. characteristics in. the shield.

Still other modifications and changes. may oo-v cur tothose skilled inthe art within the spirit and scope of theappendedclaims.

Having described our invention, we claim:

1. A- radiation beam formingnnit which-comprisesa shield having ,an internal chamber for holding a radioactive source, saidshield having a vcollirnating slot extending from anexternal wall .into said chamber for formingradiations from .said source into a beam and a, second. Slot transversely intersecting said collimatine' 51G?- and a shutter movablv mountedjin said se nd It will be understood, how

23min"- slot, said shutter being shiftable from a closed position shielding said collimating slot and interrupting said beam to another position leaving said slot clear for the passage of said beam, said shield and shutter being composed of radiation absorbing material of suficient thickness to reduce the intensity of radiation at the outer surface of said unit to a tolerable level and said second slot being so positioned that in normal use of said unit said shutter will be urged to its closed position by the force of gravity.

2. A radiation beam forming unit capable of being readily loaded and unloaded with a radioactive source without endangering operative personnel which comprises a shielding member having a central bore therein, an elongated source holder insertable in said bore directly from a shielding container thereof, said holder being composed of radiation absorbing material and having a source holding portion intermediate its length for holding a radioactive source, said shielding member having a collimating slot extending from an exterior wall into said bore at the location of said source holding portion of said holder when said holder is in place in said bore, said member also having a second slot intersecting said collimating slot at an angle thereto, and a shutter composed of radiation absorbing material movably mounted in said second slot and shiftable from an open position to a position effectively blocking the escape of radiations through said collimating slot, said second slot being directed at such an angle that in the normal use of the unit said shutter will be gravity operated to its closed position.

3. A radiation beam forming unit capable of being readily loaded and unloaded with a radioactive source without endangering operative personnel which comprises a shielding member having a central bore therein, an elongated source holder insertable in said bore, said holder being composed of radiation absorbing material and having a source holding portion intermediate its length for holding a radioactive source, said shielding member having a collimating slot extending from an exterior wall into said bore at the location of said source holding portion of said holder when said holder is in place in said bore, said member also having a second slot intersecting said collimatinng slot at an angle thereto, a shutter composed of radiation absorbing material movably mounted in said second slot and shiftable from an open position to a position effectively blocking the escape of radiations through said collimating slot, said second slot being directed at such an angle that in the normal use of the unit said shutter will be gravity operated to its closed position, and an iris associated with said collimating slot to control the cross-sectional area of said beam.

4. A unit for forming a beam of penetrative radiations from a radioactive source which comprises a generally spherical shield of radiationabsorbing material, a mounting for said shield permitting rotation thereof about an axis, said shield having an opening along said axis for the shutter of radiation absorbing material movably held in said second slot and operable by the force of gravity to closed position across said collimat-' 12 ing slot to block oil said beam and. means for opening said shutter against said force.

5. A device in accordance with claim 4 in which said means comprises a solenoid connected to said shutter by a lever system.

6. A unit for forming a beam of penetrative radiations from a radioactive source which comprises a generally spherical shield of radiation trunnions for rotatably mounting the same, the

opening in said axle being adapted to receive a radioactive source, said shield and axle having adjoining slots forming a single collimating slot extending radially outwardly from the position of said source when inserted in said axle to an external wall of said shield, said shield also having a second slot intersecting said collimating slot at an angle which is tilted downwardly in normal positions of said unit, a shutter movably held in said second slot and operable by the force of gravity to closed position across said collimating slot to block off said beam and means for opening said shutter against said force.

'7. A radiation beam forming unit comprising a shielding member having a central bore therein, an elongated source holder insertable in said bore, said holder being formed of radiation absorbing material and having a source holding portion intermediate its length for holding a radioactive source, said shielding member having a collimating slot extending from an exterior wall perpendicularly into said bore at the location or said source holding portion when said holder is in place in said bore, said shielding member also having a second slot formed therein and intersecting said collimating slot at an angle thereto, a shutter formed of radiation absorbing material slidably mounted in said second slot and movable from an open position to a position effectively blocking the escape of radiation through said collimating slot, said second slot being directed at such an angle that in the normal use of the unit said shutter will be gravity operated to its closed position, and means for moving said shutter to said open position against the force of gravity.

8. A radiation beam forming unit comprising a shielding member having a central bore therein,

place in said bore, said shielding member also having a second slot formed therein and inter sectin said collimating slot at an angle thereto, supporting tracks secured to said shielding member and disposed parallel to the axis of said sec ond slot, a shutter formed of radiation absorbing material provided with supporting bearings arranged to ride on said supporting tracks and slidable in said slot from an open position to a position effectively blocking the escape of radiation through said collimating slot, said second slot being directed at such an angle that in the normal use of the unit said shutter will be moved to its closed position by the force of gravity, a solenoid connected to said shutter through a lever system against the force of gravity, and an adjustable iris surrounding said collimating slot to control the cross-sectional area of said beam.

9. A radiation beam formin unit comprising a shielding member having a central chamber therein for holding a radioactive source, said shielding member having a collimating slot extending from an exterior wall into said central chamber, said shielding member also having a second slot formed therein and intersecting said collimating slot at an angle thereto, a shutter formed of radiation absorbing material slidably mounted in said second slot and movable from an open position to a position effectively blocking the escape of radiation through said collimating slot, said second slot being directed at such an angle that in the normal use of the unit said shutter will be gravity operated to its closed position, means connected to said shutter for movin said shutter to said open position against the force of gravity, and an adjustable iris surrounding said collimating slot to control the crosssectional area of said beam.

10. A radiation beam forming unit comprising a shielding member having a central bore therein, a mounting for said shielding member permitting rotation thereof about the axis of said bore, an elongated source holder insertable in said bore and having a source holding portion intermediate its ends for holding a radioactive source, said shielding member having a collimating slot extending from an exterior wall into said bore at the location of said source holding portion when said holder is in place in said bore, said shieldin member also having a second slot formed therein intersecting said collimating slot at an angle thereto, a shutter formed of radiation absorbing material slidably mounted in said second slot and movable from an open position to a position effectively blocking the escape of radiation through said collimating slot, said second slot being so directed that in the normal rotation of said unit about the axis of said bore said shutter will be gravity operated to its closed position, means for moving said shutter to said open position against the force of gravity, and an iris surrounding said collimating slot to control the crosssectional area of said beam.

11. A radiation beam forming unit comprising a shielding member havin a central bore therein. mounting trunnions secured to said shielding member coaxially with said bore permitting rotation of said member about the axis of said bore, an elongated source holder coextensive with said bore insertable in said bore and having a source holding portion intermediate its ends for holding a radioactive source, said shielding member having a collimating slot extending from an exterior wall into said bore at the location of said source holding portion when said holder is in place in said bore, said shielding member also having a second slot formed therein disposed perpendicular to said bore and intersecting said collimating slot at an angle thereto, a shutter formed of radiation absorbing material slidably mounted in said second slot and movable from an open position to a position effectively blockin the escape of radiations through said collimating slot, said second slot being directed at such an angle that for the rotation of said unit about the aXis of said bore encountered in normal use said shutter will be gravity operated to its closed position, electromechanical means for moving said shutter to said open position against the force of gravity, and an iris including a plurality of blocks of radiation absorbing material adjustable in position relative to the axis of said collimating slot to control the cross-sectional area of said beam.

JOHN C. PENNOCK. ALBERT J. BACCHIERI.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,206,634 Fermi et a1. July 2, 1940 2,224,077 Haupt et a1. Dec. 3, 1940 2,269,458 Kahn Jan. 13, 1942 2,474,422 Hollstein June 28, 1949 2,477,648 Piggot et a1. Aug. 2,1949 2,484,433 Turner Oct. 11, 1949 2,495,781 Silverman Jan. 31, 1950 2,514,909 Strickland July 11, 1950 2,551,491 Gilks May 1, 1951 2,594,970 Monk Apr. 29, 1952

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