Patent Number: 
Section: description

FIG. 7 is a front view of a radiation source assembly in accordance with the preferred embodiment of the present invention. As shown in the drawing, the radiation source assembly 101 comprises a pigtail 107, with a source capsule 103 and a female connector 105 respectively connected to both ends of the pigtail 107. In the assembly 101 of this invention, the pigtail 107 has the same construction as that of the conventional pigtail 7 of FIGS. 4a and 4b. That is, the pigtail 107 is an elastic rod having a round thread profile and consisting of a wire core made by twisting a plurality of carbon steel wires. A primary coil is wound around the wire core, while a secondary coil 127 is wound around the primary coil. A large-diameter coil 129, having a predetermined regular pitch, is wound around the primary coil along with the secondary coil 127. The above pigtail 107 is made of carbon steel, and so the pigtail 107 is not undesirably wear-cut or loosened even though it is used a great number of times in the same manner as that described for the conventional pigtail 7. The pigtail 107 is also free from corrosion even when its is exposed to atmospheric air. On the other hand, the source capsule 103, connected to a first end of the pigtail 107, consists of a cap connector 109, an outside cap 111 and an inside capsule 113. The cap connector 109, connected to the pigtail 107, is a cylindrical member provided with a pigtail fitting hole 115 for receiving the first end of the pigtail 107. A connecting projection 131 is provided on an end of the cap connector 109 opposite to the pigtail fitting hole 115, with the outside cap 111 being fitted over the connecting projection 131 at its fitting opening. In the assembly 101 of this invention, the pigtail 107 has a round thread profile as described above, with the large-diameter coil 129 forming screw threads. In order to allow the cap connector 109 of the source capsule 103 to engage with the first end of the pigtail 107 through a thread engagement, the connector 109 has internal round threads 119 on the pigtail fitting hole 115, with the threads 119 having a profile corresponding to the large-diameter coil 129 of the pigtail 107. In the preferred embodiment of FIG. 8, four internal round threads 119 are formed on the inside wall of the pigtail fitting hole 115 of the cap connector 109, thus engaging with four screw threads of the large-diameter coil 129 of the pigtail 107. In the preferred embodiment, the number of internal round threads 119 formed on the pigtail fitting hole 115, or four, is determined as an example since the four threads 119 are the minimum number of threads which can accomplish a desired linearity of the pigtail 107 with the cap connector 109 compression-locked to the pigtail 107. Therefore, it should be understood that four or more internal round threads 119 may be formed on the inside wall of the cap connector 109 without affecting the functioning of this invention if the number of threads 119 is not restricted by a variety of nuclear equipment standards. In order to receive the inside capsule 113, the outside cap 111 has a cavity. The inside cap 111 also has an arcuate cross-section, with the tip of the cap 111 being rounded. The object of such a rounded tip of the cap 111 is to minimize a kinetic resistance generated at the tip when the radiation source assembly 101 passes through the guide tube of a nondestructive inspection apparatus. The inside cap 111 is fitted over the connecting projection 131 of the cap connector 109 at its fitting opening prior to being integrated with the connector 109 into a single structure through a TIG welding process. In such a case, the inside capsule 113 is made of SUS 316L, and has a side length of at least 0.5 cm in order to meet the requirement disclosed in the enforcement regulations of atomic energy law. As shown in FIG. 9, the inside capsule 113, set within the outside cap 111, consists of a cylindrical capsule body 117 receiving stacked disc targets 116. A capsule lid 126 is fitted into the open end of the capsule body 117 prior to being welded to the body 117, thus sealing the capsule body 117. A coil spring 123 is set within a spring seat hole 121 of the capsule lid 126 and normally biases the disc targets 116 in a direction when the capsule lid 126 is integrated with the capsule body 117 through a welding process. The above capsule body 117 is a hollow cylindrical body, which receives the disc targets 116 therein and is open at one end thereof so as to engage with the capsule lid 126 at the open end. The capsule body 117 has an outer diameter, which allows the body 117 to be closely fitted into the outside cap 111, and has an inner diameter which is slightly larger than the diameter of the disc targets 116 so as to allow the targets 116 to be movable within the capsule body 117. The capsule lid 126, closing the capsule body 117, is a cylindrical member having an outer diameter slightly smaller than the inner diameter of the capsule body 117. The capsule lid 126 also has a flange 125 at its outside end, with the spring seat hole 121 for the target biasing spring 123 being concentrically formed at the inside end of the lid 126. Prior to a welding process of integrating the capsule lid 126 with the capsule body 117, the capsule lid 126 is fully fitted into the open end of the capsule body 117 with the flange 125 coming into close contact with the edge of the open end of the capsule body 117. When the capsule lid 126 is welded to the capsule body 117, a dedicated welding jig is used. In order to weld the capsule lid 126 to the capsule body 117, a plurality of stacked disc targets 116 are set within the capsule body 117 prior to firmly holding the capsule body 117 to the welding jig. After the capsule body 117 is held on the welding jig, the capsule lid 126, with the target biasing spring 123, is fully fitted into the open end of the body 117 prior to integrating the capsule lid 126 with the capsule body 117 into a single structure at the junction between the flange 125 of the lid 126 and the edge of the open end of the capsule body 117 through a plasma welding process or a TIG welding process. Therefore, it is possible to stably set the disc targets 116 in the form of point sources within the capsule body 117 while elastically holding the targets 116 by the spring 123 and preventing an undesirable movement of the targets 116 within the capsule body 117. When the cap connector 109 of the source capsule 103 is connected to the first end of the pigtail 107 so as to make a desired radiation source assembly 101 of this invention, the first end of the pigtail 107 engages with the cap connector 109 through a thread engagement. In such a case, the internal round threads 119 formed on the inside wall of the pigtail fitting hole 115 of the cap connector 109 act as a guide passage for the large-diameter coil 129 of the pigtail 107. After the cap connector 109 engages with the first end of the pigtail 107 through a thread engagement, the cap connector 109 is compressed at its external surface by the connector press of this invention, thus being compression-locked to the first end of the pigtail 107. In the same manner as that described for the cap connector 109, the second end of the pigtail 107 primarily engages with the female connector 105 through a thread engagement in order to connect the female connector 105 to the second end of the pigtail 107. In such a case, the internal round threads 120 formed on the inside wall of the pigtail fitting hole 114 of the female connector 105 act as a guide passage for the large-diameter coil 129 of the pigtail 107. After the female connector 105 engages with the second end of the pigtail 107, the female connector 105 is compressed at its external surface by the connector press of this invention, thus being compression-locked to the second end of the pigtail 107. In the radiation source assembly 101 of this invention, the disc targets 116 are stably set within the capsule body 117 while being elastically held by the spring 123 of the capsule lid 126 and being prevented from an undesirable movement within the capsule body 117. The disc targets 116 thus maintain desired states of point sources regardless of the number of targets 116 during a nondestructive inspecting operation, and so it is possible for the targets 116 to provide a high quality nondestructive inspection image with a precise focusing on an object. In addition, a device for biasing the capsule lid 126 is provided on the dedicated welding jig for allowing the capsule lid 126 to be welded to the capsule body 117 while maintaining the disc targets 116 in the states of point sources. It is thus possible to improve the weldability of the inside capsule 113. FIGS. 10 to 12 show the construction of a connector press 201 used for producing the radiation source assemblies 101 of this invention. As shown in the drawings, the connector press 201 accomplishes a desired compression locking of the source capsule 103, enclosing the radiation source disc targets 116, to the elastic pigtail 107 by simultaneously compressing the capsule 103 at regularly and angularly spaced points through a multi-point compressing process, thus producing a desired radiation source assembly 101. In the preferred embodiment shown in the drawings, the connector press 201 is a triple-point press as an example. The connector press 201 comprises a base 210, with a plurality of compression punches 209, a drive cylinder actuator 221, a push rod 219 and a plurality of pressure rods 213 being installed on the base 210. In the connector press 201, the compression punches 209 compress the source capsule 103 against the pigtail 107 of the assembly 101. The drive cylinder actuator 221 generates a drive force which is supplied to the compression punches 209. The one push rod 219 and the several pressure rods 213 transmit the drive force of the actuator 221 to the compression punches 209 while converting the horizontal force of the actuator 221 into a vertical force for the punches 209. The compression punches 209 are designed to compress the overlapped portion of the source capsule 103 fitted over the pigtail 107 at regularly and angularly spaced external points. In the embodiment of FIG. 11, three compression punches 209 are radially held on a punch holding disc 225 at regularly and angularly spaced positions, thus forming a triple-point compression punch unit. That is, the three compression punches 209 are regularly and radially positioned on the holding disc 225 while being spaced out at angular intervals of 120xc2x0. The punch holding disc 225 is fixed to a support 211 using a plurality of set bolts 241, with the support 211 being mounted on the base 210 of the press 201. The three compression punches 209 are movably received within three radial guide channels of a guide member 223 in a way such that the punches 209 are radially reciprocable on the holding disc 225 under the guide of the guide channels. The above guide member 223 is mounted to the holding disc 225 using a plurality of set bolts 243 with the guide channels radially positioned on the disc 225. A compression tip 227, with a compression blade 228, is provided on the inside end of each compression punch 209. In such a case, the compression tip 227 is removably attached to the inside end of each punch 209, and so it is possible to selectively attach a compression tip 227, having a radius of curvature equal to the desired compressed radius of a source capsule 103, to the inside end of each punch 209. A transverse member 234 is fixed to each of the guide channels of the guide member 223 while passing across each guide channel at an upper position while being free from interfering with a radial movement of an associated compression punch 209. Each of the transverse members 234 is connected to an associated compression punch 209 by an extension coil spring 229, or a return spring, and so the punches 209 are automatically returned to their outside positions within the guide channels of the guide member 223 due to the restoring force of the return springs 229 when the external force is removed from the punches 209. As shown in FIG. 12, the support 211, holding the punch holding disc 225, is a flat plate chamfered at its corners. A plurality of bolt holes 245 for the set bolts 241 are formed on the support 211 at regularly and angularly spaced positions on one circle. In order to rotatably hold the three pressure rods 213 for the three compression punches 209, the support 211 has three notches 247 on its outside edge at regularly spaced positions of an angular interval of 120xc2x0. A through hole 249 is perpendicularly formed on each of the notches 247, thus receiving a holding pin 251 rotatably holding an associated pressure rod 213 on the disc 225. A central hole 224 is formed at the center of the support 211 and receives a scale rod 226 which supports the outside end of the source capsule 103 of a radiation source assembly 101, the assembly 101 being held by the inside ends of the three compression punches 209. In order to hold the scale rod 226 at a desired position within the support 211, an adjusting screw 232, used for adjusting a compressing target position, is radially inserted from one chamfered top corner into the center of the support 211. A knob 236 is mounted to the outside end of the adjusting screw 232, while the body of the rod 232 is externally threaded. Therefore, the radial position of the adjusting screw 232 relative to the support 211 is adjustable by rotating the knob 236 at the outside of the support 211, thus fixing or releasing the scale rod 226 within the support 211 as desired. As shown in FIG. 10, a graduation is formed on the external surface of the scale rod 226, thus allowing a person to see the inserted length of the assembly 101 at the outside of the press 201. As shown in FIG. 10, the three pressure rods 213, inwardly pushing the compression punches 209 in a radial direction at the outside ends of the punches 209, are rotatably mounted to the notches 247 of the support 211 at their hinge points 217. The hinge point 217 of each pressure rod 213 is positioned at about ⅓ of the total length from the front end, or the punch pushing end of the pressure rod 213. The rear end of each pressure rod 213 is provided with a roller 231. The above roller 231 is set within a roller seat slit 255 formed on the rear end of the pressure rod 213 and is rotatably held within the slit 255 by a pin 253 as shown in FIGS. 10 and 14. A push block 235, coming into contact with the rollers 231 of the pressure rods 213, is a truncated conical member, with an inclined surface 233 at which the rollers 231 commonly come into movable contact with the block 235. The above push block 235 is axially moved by the drive force of the actuator 221, thus rotating the pressure rods 213 around the holding pins 251 mounted at the hinge points 217 of the pressure rods 213. The pressure rods 213 are thus opened or closed at their punch pushing ends. The push block 235 is connected to the actuator 221 through the push rod 219. The reciprocable push rod 219 is mounted to the cylinder actuator 221 and axially reciprocates by the drive force of the actuator 221, thus allowing the rollers 231 of the pressure rods 213 to be moved along the inclined surface 233 of the push block 235. The cylinder actuator 221 is horizontally installed on the base 210 by a support frame 257. The operational effect of the above connector press 201 while producing a radiation source assembly 101 will be described hereinbelow. Prior to a compression-locking process performed by the press 201, a source capsule 103, with a plurality of radiation source disc targets 116, engages with the first end of a pigtail 107. In such a case, the first end of the pigtail 107 may engage with the capsule 103 through a forcible fitting process or through a thread engagement in accordance with the kind of a desired assembly 101. After the source capsule 103 primarily engages with the first end of the pigtail 107, the assembly 101 is carefully positioned within the connector press 201 in a way such that the overlapped portion of the capsule 103 engaging with the pigtail 107 is precisely positioned within the center of the radially arranged compression punches 209 as shown in FIG. 10. The position of the assembly 101 relative to the three compression punches 209 is best seen in FIG. 13. When the position of the assembly 101 relative to the punches 209 is set, the adjusting screw 232 is loosened prior to carefully moving the scale rod 226 to the left or right until the position of the scale rod 226 is completely adjusted to accomplish a desired depth corresponding to the determined compressing target position. Thereafter, the adjusting screw 232 is tightened, thus fixing the adjusted position of the scale rod 226. When the adjusted position of the scale rod 226 is fixed as described above, it is possible to precisely set the compressing target position of the source capsule 103 which is to be compressed by the compression blades 228 of the tips 227 of the three punches 209. When the radiation source assembly 101 is completely set within the press 201, the cylinder actuator 221 is turned on, thus axially moving the push rod 219 along with the push block 235 toward the support 211. Due to such a movement of the push block 235 toward the support 211, the rollers 231 of the pressure rods 213 simultaneously roll up along the inclined surface 233 of the truncated conical push block 235. When the rollers 231 of the pressure rods 213 roll upwardly along the inclined surface 233 of the push block 235, the three pressure rods 213 are rotated clockwise around the hinge points 217 in FIG. 10. Therefore, each of the three pressure rods 213 inwardly biases an associated one of the three compression punches 209 in a radial direction of the holding disc 225 with a force stronger than that applied to the roller 231 three times due to a leverage effect. In such a case, the three compression punches 209 move radially and inwardly at the same time under the guide of the guide channels of the guide member 223 shown in FIG. 11, thus synchronously compressing the target portion of the source capsule 103 by their compression blades 228 at three points. After the compression locking process performed by the three punches 209, the push rod 219 moves toward the cylinder actuator 221, thus returning to its original position. In such a case, the push block 235,also returns to its original position while allowing the rollers 231 of the pressure rods 213 to roll down along the inclined surface 233 of the push block 235. Therefore, the pressure rods 213 are rotated counterclockwise around the hinge points 217 in FIG. 10, thus removing the biasing force from the three compression punches 209. Therefore, the compression punches 209 automatically move outwardly in the radial direction by the restoring force of the return springs 229, thereby allowing the assembly 101 to be removed from the press 201. As described above, the present invention provides a radiation source assembly. In the assembly, the cap connector of a radiation source capsule and the female connector engaging with the male connector of a manipulation handle are each provided with internal round threads on its pigtail fitting hole. Each of the two connectors thus engages with the large-diameter coil of the pigtail at the internal round threads through a thread engagement prior to being compressed at a target portion by a plurality of compression punches of a connector press. Therefore, the two connectors, which are threaded with and compression-locked to both ends of the pigtail, are almost completely prevented from an unexpected removal from the pigtail different from a conventional assembly wherein the two connectors engage with the pigtail through a forcible fitting engagement prior to being compression-locked to the pigtail. In addition, the radiation source assembly of this invention allows a person to know whether both ends of the pigtail fully reach desired points within the two connectors, thus securing a precise compressing target portion. In the assembly of this invention, the inserted lengths of the pigtail relative to the two connectors are maximized, thus accomplishing a desired linearity of the assembly. Therefore, it is thus possible for a user to precisely, appropriately and safely use the radiation source assembly of this invention during a nondestructive inspecting operation. In addition, the assembly of this invention effectively minimizes the frictional resistance generated at the source capsule when the capsule repeatedly moves within a guide tube in opposite directions. The assembly is thus almost completely free from an operational error or being abrasion-damaged, or an unexpected radioactive contamination. The present invention also secures a uniform length of the radiation source assemblies, thus allowing the assemblies to be precisely and firmly installed at desired positions within nondestructive inspecting apparatuses or within dedicated carriers. This finally and effectively reduces a radiation leakage from the assembly. In the radiation source assembly of this invention, a target biasing spring is provided on the capsule lid for allowing the disc targets within the inside capsule of the source capsule to effectively maintain a desired condition as point sources regardless of the number of targets, with the capsule lid being fitted into and welded to a capsule body of the inside capsule. Therefore, the assembly of this invention provides a high quality nondestructive inspection image with a precise focusing on an object. In addition, a capsule lid biasing device is provided on a dedicated welding jig of this invention for allowing the capsule lid to be welded to the capsule body of the inside capsule while being biased by the device. Therefore, it is possible to prevent inert gas from being undesirably introduced into the inside capsule through the junction between the capsule body and the capsule lid during a TIG welding process performed in an inert gas atmosphere. This finally accomplishes a welding process for the inside capsule of the source capsule while maintaining the disc targets in the states of point sources and improves the weldability of the source capsule. The present invention also provides a connector press used in producing the radiation source assemblies. The connector press of this invention accomplishes a desired compression locking of the source capsule to the elastic pigtail by simultaneously compressing the capsule at regularly and angularly spaced points through a multi-point compressing process. The connector press of this invention thus applies a uniform compressing force to the compressing target portion of the capsule engaging with the pigtail, and so the press accomplishes a desired linearity of the capsule and the pigtail. Therefore, when the assembly of this invention is used in a nondestructive inspecting operation with the source capsule repeatedly moving within a radiation shield guide tube in opposite directions, the assembly is free from being exceedingly bent at the compression-locked portion. This finally prevents the assembly from causing an operational error or being abrasion-damaged due to a frictional resistance generated at such a bent portion, thus accomplishing a desired operational safety of the assembly. Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.