Patent Publication Number: US-6707875-B2

Title: Nonintrusive inspection apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present patent application is a divisional of prior application No. 10/071,655, filed Feb. 7, 2002 now U.S. Pat. No. 6,590,956, entitled A NONINTRUSIVE INSPECTION SYSTEM, which is a divisional of prior application Ser. No. 09/794,505, filed Feb. 26, 2001, entitled A NONINTRUSIVE INSPECTION SYSTEM, which issued on Aug. 6, 2002 as U.S. Pat. No. 6,430,255, which is a continuation of prior application No. PCT/US99/28229, filed Nov. 29, 1999, which claims priority from U.S. Provisional Patent Application No. 60/110,417, filed on Nov. 30, 1998. 
    
    
     BACKGROUND TO THE INVENTION 
     1.) Field of the Invention 
     This invention relates to an x-ray technique-based nonintrusive inspection apparatus. An x-ray technique-based nonintrusive inspection apparatus according to the invention may, for example, be used for nonintrusively inspecting closed containers before being loaded into a loading bay of an aircraft, or may include technologies which may find application in other similar or different inspection apparatus. 
     2.) Discussion of Related Art 
     Inspection apparatus are commonly used for nonintrusively inspecting luggage and other closed containers before being loaded into a loading bay of an aircraft. Older generation inspection apparatus relied merely on conventional x-ray technology for nonintrusively inspecting closed containers. More recently, inspection apparatus which rely on computer tomography (CT) scanning technology have also been utilized. An inspection apparatus utilizing CT scanning technology is described in U.S. Pat. Nos. 5,182,764 and 5,367,552 by Peschmann et al. which are assigned to the assignee of the present case and which are hereby incorporated by reference. 
     SUMMARY OF THE INVENTION 
     The invention provides an x-ray technique-based nonintrusive inspection apparatus which allows for “radiation locking” as will be described in more detail in the description that follows. The inspection apparatus includes loading inspection and unloading tunnel sections, first, second and third conveyor apparatus, an x-ray source, first, second, third and fourth actuation devices, and first, second, third and fourth radiation resistant closure members. 
     Each tunnel section has a respective first end and a respective second end opposing the first end thereof. The inspection tunnel section is located in line after the loading tunnel section so that the second end of the loading tunnel section is adjacent the first end of the inspection tunnel section. The unloading tunnel section is located in line after the inspection tunnel section so that the second end of the inspection tunnel section is located adjacent the first end of the unloading tunnel section. 
     The first conveyor apparatus has at least one conveyor belt which is at least partially located within the loading tunnel section and which, upon movement, is capable of moving an object from the first end of the loading tunnel section to the second end of the loading tunnel section. The second conveyor apparatus has at least one conveyor belt which is at least partially located within the inspection tunnel section and which, upon movement, is capable of moving an object from the first end of the inspection tunnel section to the second end of the inspection tunnel section. The third conveyor apparatus has at least one conveyor belt which is at least partially located within the unloading tunnel section and which, upon movement, is capable of moving an object from the first end of the unloading tunnel section to the second end of the unloading tunnel section. 
     The x-ray source, when operated, creates radiation within the inspection tunnel section. 
     The first closure member is movable by the first actuation device between an open position wherein the first end of the loading tunnel section is open, and a dosed position wherein the first closure member closes the first end of the loading tunnel section. The second closure member is movable by the second actuation device between an open position wherein the second end of the loading tunnel section is in communication with the first end of the inspection tunnel section to allow for movement of an object from the loading tunnel section to the inspection tunnel section, and a dosed position wherein the second closure member substantially closes off communication between the first and inspection tunnel sections. The third closure member is movable by the third actuation device between an open position wherein the second end of the inspection tunnel section is in communication with the first end of the unloading tunnel section to allow for movement of an object from the inspection tunnel section to the unloading tunnel section, and a closed position wherein the third closure member substantially doses off communication between the second and unloading tunnel sections. The fourth closure member is movable by the fourth actuation device between an open position wherein the second end of the loading tunnel section is open, and a dosed position wherein the fourth closure member closes the second end of the unloading tunnel section. 
     The inspection apparatus may further include first, second, third and fourth curtain rollers, each being rotatable by a respective one of the actuation devices. The closure members may be curtains and each curtain may be secured to a respective curtain roller so as to be rolled onto or from the curtain roller upon rotation of the curtain roller. 
     The inspection apparatus may further include a controller which controls power supplied to the respective actuation devices. The controller may be programmed to synchronize the actuation devices so that, at least when the x-ray source creates radiation within the inspection tunnel section, at least one of the first and second closure members is in its respective closed position and at least one of the third and fourth closure members is in its respective dosed position. The controller may turn the radiation source off when both the first and second closure members are not entirely in their respective dosed positions, or when both the third and fourth closure members are not entirely in their respective dosed positions. 
     The invention also provides a method of nonintrusively inspecting an object in a “radiation locking” manner, utilizing an x-ray technique-based nonintrusive inspection apparatus, that permits x-rays generated in an inspection tunnel section thereof to remain on continuously. A first radiation resistant closure member is moved into an open position wherein a first end of a loading tunnel section is open, while a second radiation resistant closure member is in a closed position wherein it doses a second end of the loading tunnel section opposing the first end of the loading tunnel section. An object is moved through the first end of the loading tunnel section into the loading tunnel section while the second closure member remains in its closed position. The first closure member is then moved into a dosed position wherein the first closure member doses the first end of the first tunnel. After movement of the first closure member into its dosed position, the second closure member is moved into an open position wherein the second end of the loading tunnel section is in communication with a first end of a inspection tunnel section. The object is then moved from the loading tunnel section into the inspection tunnel section. After movement of the object into the inspection tunnel section, the second closure member is moved into its closed position so as to substantially close off communication between the first and inspection tunnel sections. The object is then radiated within the inspection tunnel section. 
     The confines of the inspection tunnel section may be radiated while the object is moved into the loading tunnel section. 
     The first closure member may remain in its closed position while the object is moved into the inspection tunnel section. The confines of the inspection tunnel section may be radiated while the object is moved into the inspection tunnel section. 
     The invention also provides a method of nonintrusively inspecting an object by simultaneously utilizing an x-ray line scanner subsystem and a CT scanner subsystem, in an x-ray technique-based nonintrusive inspection apparatus, which may be in a dose relationship relative to one another. A front portion of the object is first scanned utilizing the x-ray line scanner subsystem. A section within the front portion of the object is scanned utilizing a CT scanner subsystem. A rear portion of the object is then scanned, utilizing the x-ray line scanner subsystem, after the section in the front portion is scanned utilizing the CT scanner subsystem. 
     The object may, for example, be a dosed container which is nonintrusively inspected. 
     The object may be scanned while being moved relative to the x-ray line scanner subsystem and the CT scanner subsystem, and the front portion and the rear portion may be scanned without altering the direction of movement of the object relative to the x-ray line scanner subsystem and the CT scanner subsystem, although it may be necessary to bring the object to a halt relative to the CT scanner subsystem. Movement of the object relative to the x-ray line scanner subsystem and the CT scanner subsystem may be progressively reduced after the section is scanned by the x-ray line scanner subsystem but before the section is scanned by the CT scanner subsystem. 
     The invention also provides an x-ray technique-based nonintrusive inspection apparatus having both x-ray and CT scanning capabilities within a single tunnel section. The inspection apparatus includes at least one tunnel section, a conveyor apparatus, an x-ray line scanner subsystem, and a CT scanner subsystem. The tunnel section has first and second opposed ends. The conveyor apparatus has at least one conveyor belt which is at least partially located within the tunnel section. The conveyor belt, upon movement, is capable of transporting an object from the first end to the second end of the tunnel section. The x-ray line scanner subsystem is positioned to scan at a first plane within the tunnel section. The CT scanner subsystem is positioned to scan at a second plane within the tunnel section. 
     The first and second planes may be located by distance of less than 110 centimeters from one another. 
     Preferably, the same conveyor belt conveys the object from the first plane to the second plane. 
     The inspection apparatus may further include a base frame, and a support structure having a lower end secured to the base frame and extending upwardly therefrom, and the x-ray line scanner subsystem and the CT scanner subsystem may both the mounted to the support structure. 
     The invention also provides an x-ray technique-based nonintrusive inspection apparatus having good structural integrity. The inspection apparatus includes a base frame of monocoque design, a support structure, and a CT scanner subsystem. The support structure is secured to the base frame. The CT scanner subsystem is rotatably mounted to the support structure. Although having specific application for x-ray technique-based nonintrusive inspection apparatus used for detecting contraband in closed containers, inspection apparatus are also envisioned having base frames of monocoque design which are not necessarily used for the detection of contraband within closed containers. 
     A motor may be coupled to the CT scanner subsystem so as to rotate the CT scanner subsystem, for example at a rate of at least 100 revolutions per minute. 
     The CT scanner subsystem may define an opening having a cross-dimension of at least 110 centimeters. 
     The CT scanner subsystem may define an opening and the inspection apparatus may further include a conveyor apparatus mounted to the base frame. The conveyor apparatus may have a conveyor belt which passes through the opening. The conveyor belt may have a width of at least 90 cm. 
     The CT scanner subsystem may include a gantry enclosure, a radiation source mounted on one side to the gantry enclosure so that, when the radiation source is operated, the confines of the gantry enclosure are radiated, the gantry enclosure being at least partially made of lead. 
     The invention also provides a CT scanner subsystem of a nonintrusive inspection system which is at least partially self shielded so as to attenuate leaking of radiation therefrom to acceptable levels. The CT scanner subsystem may include first and second spaced gantry plates, at least one spacer, a ring, and an x-ray source. The first and second gantry plates each have a respective gantry aperture formed therein. The at least one spacer is located between the gantry plates so that the at least one spacer together with the gantry plates define a partial gantry enclosure. The ring is located on the gantry enclosure and allows the gantry enclosure to be mounted to a support structure for rotation about an axis through the gantry apertures. The x-ray source is secured to the gantry enclosure at one side thereof so that, when the x-ray source is operated, the confines of the gantry enclosure are at least partially radiated. The gantry enclosure is at least partially made of a material which substantially attenuates radiation leakage from the gantry enclosure i.e. by a degree which is much more than for example attenuation of radiation with steel. The gantry enclosure may for example include a liner of lead or another material which, substantially attenuates radiation leakage on the first or second gantry plates or on the spacer. The x-ray source may include an x-ray tube and a liner, of lead or another material which substantially attenuates radiation leakage, on the x-ray tube. 
     The invention also provides an x-ray technique-based noninstrusive inspection apparatus including a support frame, a CT scanner subsystem, and a tunnel portion. The CT scanner subsystem may include first and second spaced gantry plates, at least one spacer, and an x-ray source. Each gantry plate may have a respective gantry aperture formed therein. The at least one spacer may be located between the gantry plates so that the at least one spacer together with the gantry plates define a partial gantry enclosure. The x-ray source may be secured to the gantry enclosure at one side thereof so that, when the x-ray source is operated, the confines of the gantry enclosure are at least partially radiated. The gantry enclosure is at least partially made of a material which substantially attenuates radiation leakage from the gantry enclosure. The CT scanner subsystem is mounted to the support frame for rotation about an axis through the first and second gantry apertures. The tunnel portion is nonrotatably mounted to the support frame and has an end which mates with the gantry aperture in the first gantry plate. The tunnel portion is also at least partially made of a material which substantially attenuates radiation leakage from the tunnel portion. 
     The invention also provides an x-ray technique-based noninstrusive inspection apparatus which is easily maintainable because of the location of a flexible member such as a belt or a chain which is used for driving a CT scanner subsystem of the inspection apparatus. The inspection apparatus includes a support frame, a CT scanner subsystem, at least first, second and third pulleys, and a flexible member. The CT scanner subsystem is rotatably mounted to the support frame and has a circular outer surface. The first, second and third pulleys are mounted around the CT scanner subsystem to the support frame. The flexible member runs over the first, second and third pulleys. A first section of the flexible member runs from the first pulley to the second pulley in a first direction around and over the circular outer surface. A second section of the flexible member returns from the second pulley over the third pulley back to the first pulley in a second direction, opposite to the first direction, around the circular outer surface. 
     According to one aspect of the invention, an x-ray technique-based nonintrusive inspection apparatus is provided including at least a first tunnel section, an x-ray source, at least a first actuation device, and at least a first radiation resistant closure member. The first tunnel section has first and second opposed ends. The x-ray source, when operated, creates radiation within the first tunnel section. The first radiation resistant closure member is movable by the actuation device between an open position wherein the first end of the first tunnel section is open, and a closed position wherein the first closure member closes the first end of the first tunnel section. The inspection apparatus thus has an “active” closure member. Specific advantages of active closure members are discussed in the description that follows. 
     The inspection apparatus may include a tensioning roller which is rotatably mounted to the support frame. The tensioning roller acts on the curtain and tends to roll the curtain from the curtain roller. 
     The inspection apparatus may further include a spring which is biased between the support frame and the tensioning roller so as to tend to rotate the tensioning roller. 
     The inspection apparatus may further include a sheet which has a first portion attached to the curtain roller and a second portion attached to the tensioning roller, so as to connect the tensioning roller to the curtain. The sheet may be secured to the curtain roller without intervention by the curtain. 
     The curtain preferably hangs from one side of the curtain roller and the tensioning roller is preferably located on the same side of the curtain roller as the side of the curtain roller from which the curtain hangs. 
     The invention also provides an effective manner of making a collimator for a detector array of the x-ray detection apparatus. First, a die is injected with a material. The material is then allowed to set within the die to form a body. The body is then removed from the die. The body typically includes a support structure and a plurality of septa secured to the support structure. 
     The material preferably includes a first, lead component comprising at least 90 percent thereof. The material may include a second component which is stronger than lead. The second component may, for example, include tin. 
     According to the method, a collimator for a detector array may be formed wherein septa of the collimator converge. The collimator may include a body which includes a support structure and a plurality of septa secured to the support structure. Center lines of two of the septa located next to one another converge in a first direction so that the septa may be aligned with a radiation source, but surfaces of the two septa facing one another do not converge in the first direction so as to allow for removal of the body from a die which is used to form the body. 
     The invention also provides a collimator for a detector array of an x-ray inspection apparatus, which includes a body which includes at least one support structure and a plurality of septa secured to the support structure. The body is made of a material having a first, lead component comprising at least 90 percent thereof. 
     For added strength, the body may include first and second support structures with the septa secured between the first and second support structures. 
     The invention also provides a collimator for a detector array of an x-ray inspection apparatus which allows for modular design of detector arrays. The collimator includes a body having a plurality of registration formations thereon. The body includes a support structure and a plurality of septa secured to the support structure. 
     Each registration formation may be a respective notch in a portion of the body. 
     The invention also provides an x-ray technique-based nonintrusive inspection apparatus which allows for easy release of parts of containers which become jammed between rollers of conveyor apparatus which are located sequentially one after the other. The inspection apparatus includes a base frame, a tunnel section, a conveyor belt mounting structure, front and rear conveyor rollers, and a conveyor belt. The tunnel section has a first end and a second end opposing the first end, and is mounted to the base frame. The front and rear rollers are rotatably mounted to the conveyor belt mounting structure. The conveyor belt runs over the front and rear conveyor rollers. The conveyor belt mounting structure is mounted to the base frame for at least limited movement, between first and second positions, in a direction in which the conveyor belt moves between the front and rear conveyor rollers. The conveyor belt extends at least some distance between the first and second ends through the tunnel section. 
     The invention also extends to a method of assembling an x-ray technique-based nonintrusive inspection apparatus wherein a conveyor belt of the inspection apparatus is preinstalled and wherein the conveyor belt may be pre-tensioned. A conveyor belt mounting structure, having front and rear conveyor rollers rotatably mounted thereto, and a conveyor belt over the front and rear conveyor rollers, is mounted to a base frame. The conveyor belt mounting structure is mounted to the base frame for at least limited movement between first and second positions in a direction in which the conveyor belt moves over the front and rear conveyor rollers. 
     The invention also provides an x-ray technique-based nonintrusive inspection apparatus having a housing which is designed, for purposes of keeping contaminants from entering the housing, to have a higher pressure inside the housing than externally of the housing. The nonintrusive inspection apparatus includes a base frame, tunneling, an x-ray source, paneling, and a fan. The tunneling is mounted to the base frame and has a first end and a second end opposing the first end. The x-ray source which, when operated, creates radiation within the tunneling. The paneling is located around the tunneling and the x-ray source so that the paneling and the base frame jointly define a housing around the tunneling and the x-ray source. The housing has an entry aperture in proximity to the first end, and an exit aperture in proximity to the second end of the tunneling. The housing also has an air inlet opening. The fan is positioned to draw air through the inlet opening into the housing. The housing is formed, the entry aperture seals with the first end of the tunneling to an extent sufficient, and the exit aperture seals with the second end of the tunneling to an extent sufficient so that the confines of the housing are at a higher pressure than externally of the housing when the fan draws into the housing. 
     The invention also provides an x-ray technique-based nonintrusive inspection apparatus which may be cooled without necessarily having a fan mounted to a rotating gantry enclosure thereof. The nonintrusive inspection apparatus includes a support frame, a CT scanner subsystem, a plenum, an air-conditioning unit, and a duct. The CT scanner subsystem is rotatably mounted to the support frame and has a gantry enclosure. At least one air passage is formed into the gantry enclosure. The plenum is nonrotatably mounted to the support frame. The plenum is located externally of the gantry enclosure over the air passage so that the confines of the plenum are in communication with the air passage. The air-conditioning unit includes a fan. The duct connects the air-conditioning unit with the plenum. When the fan is operated, air passes from the air-conditioning unit through the duct to the plenum, from the plenum through the air passage into the gantry enclosure, and from the gantry enclosure through the radiator. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention is further described by way of example with reference to the accompanying drawings wherein like reference numerals indicate like or similar components and wherein: 
     FIG. 1 is a perspective view of an x-ray technique-based nonintrusive inspection apparatus according to an embodiment of the invention; 
     FIG. 2 is a cross-sectional side view representing some of the components of the inspection apparatus of FIG. 1; 
     FIG. 3 a  is a side view representing the inspection apparatus of FIG. 2 before a first container and a second container are moved into a loading tunnel section of the inspection apparatus; 
     FIG. 3 b  is a view similar to FIG. 3 a  after the first container is moved into the loading tunnel section; 
     FIG. 3 c  is a view similar to FIG. 3 b  after a first radiation resistant curtain is closed behind the first container; 
     FIG. 3 d  is a view similar to FIG. 3 c  after a second radiation resistant curtain in front of the first container is opened; 
     FIG. 3 e  is a view similar to FIG. 3 d  while the first container is moved into and inspection tunnel section of the inspection apparatus; 
     FIG. 3 f  is a view similar to FIG. 3 e  after the first container is located entirely within the inspection tunnel section and the second radiation resistant curtain is dosed behind the first container; 
     FIG. 3 g  is a view similar to FIG. 3 f  after a third radiation resistant curtain in front of the first container is opened and while the first container is moved into an unloading tunnel section of the inspection apparatus, and after the second container is moved into the loading tunnel section; 
     FIG. 3 h  is a view similar to FIG. 3 g  after the first container is located entirely within the unloading tunnel section and the third radiation resistant curtain is closed behind the first container, and after the first radiation resistant curtain is closed behind the second container; 
     FIG. 3 i  is a view similar to FIG. 3 h  after a fourth radiation resistant curtain in front of the first container is opened and the first container is moved out of the unloading tunnel section, and after the second radiation resistant curtain is opened in front of the second container; 
     FIG. 3 j  is a view similar to FIG. 3 i  after the fourth radiation resistant curtain is closed behind the first container, after the second container is moved into the inspection tunnel section, and after the second radiation resistant curtain is dosed behind the second container; 
     FIG. 4 a (i) is a view similar to FIG. 3 e , further illustrating the positioning of the container relative to an imaging plane of an x-ray line scanner subsystem forming part of the inspection apparatus; 
     FIG. 4 a (ii) is a plan view of the container in FIG. 4 a (i); 
     FIG. 4 b (i) is a view similar to FIG. 3 f , further illustrating the positioning of the container relative to the imaging plane of the x-ray line scanner subsystem and an imaging plane of a CT scanner subsystem forming part of the inspection apparatus when the CT scanner subsystem is used for scanning at a location of interest within the container that may correspond with an object of interest; 
     FIG. 4 b (ii) is a plan view of the container in FIG. 4 b (i); 
     FIG. 4 c (i) is a view similar to FIG. 3 g , further illustrating the positioning of the container relative to the respective imaging planes of the x-ray line scanner subsystem and the CT scanner subsystem when the CT scanner subsystem is used for scanning another location of interest within the container; 
     FIG. 4 c (ii) is a plan view of the container in FIG. 4 c (i); 
     FIG. 5 is a perspective view of a support frame forming part of the inspection apparatus and the CT scanner subsystem; 
     FIG. 6 is a cross-sectional side view which illustrates how radiation is shielded within the inspection tunnel section; 
     FIG. 7 is a perspective view illustrating in exploded form a gantry enclosure forming part of the CT scanner subsystem; 
     FIG. 8 is an end view illustrating a driving arrangement which is used for rotating the CT scanner subsystem; 
     FIG. 9 is a perspective view of a shielding arrangement which is incorporated into a shielding apparatus forming part of the x-ray technique-based nonintrusive inspection apparatus; 
     FIG. 10 is an end view of the shielding arrangement of FIG. 9 before a radiation resistant curtain thereof is rolled onto a curtain roller thereof; 
     FIG. 11 is a view similar to FIG. 10 while the curtain is rolled onto the curtain roller, further illustrating the effect of a tensioning apparatus which controls rolling of the curtain onto the curtain roller; 
     FIG. 12 a (i) is a cross-sectional side view of a die which is used to form a detector array collimator of the inspection apparatus, illustrating the die in exploded form; 
     FIG. 12 a (ii) is a cross-sectional end view of the die of FIG. 12 a (i); 
     FIG. 12 b (i) is a view similar to FIG. 12 a (i) after the die is assembled and before a material is injected into the die; 
     FIG. 12 b (ii) is a cross-sectional end view of the die in FIG. 12 b (i); 
     FIG. 12 c (i) is a cross-sectional view of a detector array collimator which is formed by injecting a material into the die of FIG. 12 b (i); 
     FIG. 12 c (ii) is a cross-sectional end view of the detector array collimator of FIG. 12 c (i); 
     FIG. 13 is a perspective view of the detector array collimator of FIG. 11 c (i) and FIG. 11 c (ii); 
     FIG. 14 is a cross-sectional view through septa of the detector array collimator of FIG. 13, illustrating in an exaggerated manner how the septa are formed; 
     FIG. 15 is a perspective view of a portion of the inspection apparatus, illustrating how a conveyor system of the inspection apparatus is mounted to a base frame of the inspection apparatus; 
     FIG. 16 is a side view of the inspection apparatus, further illustrating paneling which partially form a housing of the inspection apparatus; and 
     FIG. 17 is a side view of the inspection apparatus illustrating diagrammatically how the inspection apparatus is air-conditioned; 
    
    
     DESCRIPTION OF THE INVENTION 
     Introductory Description 
     FIG.  1  and FIG. 2 of the accompanying drawings illustrate an x-ray technique-based nonintrusive inspection apparatus  8  according to an embodiment of the invention. The inspection apparatus  8  includes a support frame  10 , a loading tunnel section  12 , an inspection tunnel section  14 , an unloading tunnel section  16 , a loading conveyor apparatus  18 , and inspection conveyor apparatus  20 , an unloading conveyor apparatus  22 , first, second, third and fourth shielding arrangements,  24 ,  26 ,  28  and  30  respectively, a stationary x-ray line scanner subsystem  32 , a rotating CT scanner subsystem  34 , and a controller  36 . 
     The support frame  10  includes a base frame  38  and an arch  40  which arches in a plane perpendicular to the drawing and which is secured to the base frame  38  on opposing sides of the arch  40 . The x-ray line scanner subsystem  32  is mounted on one side of the arch  40  and the CT scanner subsystem  34  is mounted to the arch  40  for rotation in a plane perpendicular to the drawing on a side of the arch  40  opposing the x-ray line scanner subsystem  32 . 
     Referring now in particular to FIG. 2, each tunnel section  12 ,  14  or  16  has a respective first end  42  and a respective second end  44  opposing the first end thereof. The inspection tunnel section  14  is located in line after the loading tunnel section  12  so that the second end  44  of the loading tunnel section  12  is adjacent the first end  42  of the inspection tunnel section  14 . The unloading tunnel section  16  is located in line after the inspection tunnel section  14  so that the second end  44  of the inspection tunnel section  14  is located adjacent the first end  42  of the unloading tunnel section  16 . All the tunnel sections  12 ,  14  and  16  are mounted to the base frame  38 . 
     Each conveyor apparatus  18 ,  20  or  22  is located within a respective tunnel section  12 ,  14  or  16 . Each conveyor apparatus  18 ,  20  or  22  includes a respective front conveyor roller  46  near a respective first end  42  of a respective tunnel section  12 ,  14  or  16 , a respective rear conveyor roller  48  near a respective second end  44  of a respective tunnel section  12 ,  14  or  16 , and a conveyor belt  50  which runs over the conveyor rollers  46  and  48  and a supporting bed (not shown). Although not shown in FIG. 2 so as not to obscure the drawing, it should be understood that each conveyor roller  46  and  48  of each conveyor apparatus  18 ,  20  and  22  is rotatably mounted to a respective bracket assembly and that each bracket assembly is secured to the base frame  38 . It should also be understood that one of the conveyor rollers  46  or  48  of each conveyor apparatus  18 ,  20  and  22  is rotated by a respective motor which is mounted to the base frame  38  but which is not shown in FIG. 2 so as not to obscure the drawing. 
     Each shielding arrangement  24 ,  26 ,  28  and  30  includes a respective curtain roller  54  and a respective radiation resistant curtain  56  secured to the curtain roller  54 . Although not shown in FIG. 2 so as not to obscure the drawing, it should be understood that each curtain roller  54  is rotatably mounted to a respective support structure and that each support structure is secured to the base frame  38 . It should also be understood that each curtain roller  54  is rotated by a respective motor which may also be mounted to the support structure but which is not shown in FIG. 2 so as not to obscure the drawing. The curtain rollers  54  are positioned so that each curtain  56  is located near an end  42  or  44  of one or more of the tunnel sections  12 ,  14  and  16 . 
     Rotation of the curtain roller  54  in one direction causes the curtain  56  to be rolled from the curtain roller  54  which causes the curtain  56  to drop, and rotation of the curtain roller  54  in an opposite direction raises the curtain  56  by rolling the curtain  56  onto the curtain roller  54 . 
     When the curtain  56  is raised, the curtain  56  is moved into an “open position” wherein the end or ends  42  or  44  are open, and when the curtain is dropped the curtain is moved into a “closed position” wherein the curtain  56  doses the end or ends  42  or  44 . 
     For example, when the curtain  56  of the first shielding arrangement  24  is moved into its open position, the first end  42  of the loading tunnel section  12  is open, and when the curtain  56  of the first shielding arrangement  24  is moved into its closed position, the first end  42  of the loading tunnel section  12  is dosed. 
     Similarly, when the curtain  56  of the second shielding arrangement  26  is moved into its open position, the second end  44  of the loading tunnel section  12  is in communication with the first end  42  of the inspection tunnel section  14 , and when the curtain  56  of the second shielding arrangement  26  is moved into its open position, communication between the loading and inspection tunnel sections  12  and  14  is substantially dosed off. 
     Similarly, when the curtain  56  of the third shielding arrangement  28  is moved into its open position, the second end  44  of the inspection tunnel section  14  is in communication with the first end  42  of the unloading tunnel section  16 , and when the curtain  56  of the third screening arrangement  28  is moved into its closed position, communication between the inspection and unloading tunnel sections  14  and  16  is substantially closed off. 
     Similarly, when the curtain  56  of the fourth shielding arrangement  30  is moved into its open position, the second end  44  of the unloading tunnel section  16  is open, and when the curtain  56  of the fourth shielding arrangement  30  is moved into its dosed position, the second end  44  of the unloading tunnel section  16  is dosed. 
     Detectors (not shown) are positioned to detect the positioning of each curtain  56  independently. More detectors (not shown) are positioned to detect the positioning, speed and acceleration of each conveyor belt  50  independently. More detectors (not shown) are positioned to detect the positioning of containers at various locations within the inspection apparatus  8 . 
     The controller  36  is in communication with the detectors. A disk or other computer readable medium may be provided on which an executable program is stored. The controller  36  may, for example, be a computer which is capable of reading the program on the disk and may include memory in the program is stored. The program, once executed may automatically synchronize movement of the curtains  56  and the conveyor belts  50  in a manner which is generally referred to as “radiation locking”. Radiation locking is further described hereinbelow with reference to FIG. 3 a  to FIG. 3 j . The controller  36  also controls other aspects of movement of containers through the inspection apparatus  8  which are further described hereinbelow with reference to FIG. 4 a (i) to FIG. 4 c (ii). It can generally be noted that this stage that radiation locking provides adequate shielding of x-ray radiation from people that may be located in an area around the inspection apparatus  8 . The controller  36  controls power supplied to the motors which drive the conveyor apparatus  18 ,  20  and  22  so as to control the positioning, speed and acceleration of the conveyor belts  50  of the conveyor apparatus  18 ,  20  and  22 . The controller  36  also controls power supplied to the motors which drive the curtain rollers  54  of the first, second and third shielding arrangement  24 ,  26 ,  28  and  30  so as to control the positioning, speed and acceleration of the curtain rollers  54  of the first, second and third shielding arrangement  24 ,  26 ,  28  and  30 . 
     One advantage of the inspection apparatus  8  illustrated in FIG. 2 is that, because of adequate shielding due to radiation locking, there is no need for locating the conveyor apparatus  18 ,  20  and  22  so that they define an elaborate undulating path—the conveyor belts  50  are all linearly aligned with one another, and are located within the same horizontal plane (if, of course, the inspection apparatus  8  is located on a horizontal floor). When a technician has to enter any one of the tunnel sections  12 ,  14  or  16 , the technician may easily enter the tunnel section without the need for the technician to climb up an inclined conveyor apparatus, as is often the case in certain prior art apparatus. 
     A further advantage of the fact that the conveyor belts  50  are all linearly aligned is that the height of the overall apparatus can be minimized. In one example the inspection apparatus  8 , ones enclosed by a housing, has an overall height of about 223 centimeters. A further advantage is that the maximum speed of objects passing through the inspection apparatus  8  is not constrained by the existence of discontinuities in the belt path. 
     A further advantage of the inspection apparatus  8  is that the curtains  56  are “active curtains” in the sense that each curtain  56  opens to allow for a container to pass  56  without obstruction by the curtain  56 . The curtain  56  does therefore not create a volume of “dead space” by lying on top of the container. Larger objects can therefore be moved into a respective tunnel section  12 ,  14  or  16  although each conveyor apparatus  18 ,  20  or  22  may have a smaller footprint. Larger containers are typically about 110 centimeters in length and in one example the loading tunnel section  12  has a length of about 135 centimeters and the unloading tunnel  16  has a length of about 135 centimeters. Because dead space is minimized, the overall length of the apparatus is thus decreased. Active curtains also have the advantage that they may allow for passing through of heavier containers, which may for example be as much as one meter in height, but that very light weight containers may also pass through without being obstructed, there being no absolute minimum weight requirement for passing through the active curtains. Larger light objects in particular may pass through easier than through prior art passive curtains. 
     It should also be noted that the x-ray line scanner subsystem  32  and the CT scanner subsystem  34  operate within the same tunnel section, namely the inspection tunnel section  14 , without an intermediate radiation resistant curtain or other shielding device. By locating the x-ray line scanner subsystem  32  and the CT. scanner subsystem  34  within the same tunnel section, the overall length of the inspection apparatus  8  is reduced. As will be described in more detail hereinbelow, collimators prevent, or limit, interference between x-rays of the x-ray line scanner subsystem  32  and the CT. scanner subsystem  34 . 
     Furthermore, it should be noted that the x-ray line scanner subsystem  32  and the CT scanner subsystem  34  are both mounted to the same upwardly extending support structure, namely the arch  40 . By mounting the x-ray line scanner subsystem  32  and the CT scanner subsystem  34  both to the same support structure, the orientation of the x-ray line scanner subsystem  32  and the CT scanner subsystem  34  relative to one another can be more accurately controlled. In particular, the x-ray line scanner subsystem  32  may scan in a first plane and the CT scanner subsystem  34  may scan in a second plane which is parallel to the first plane to a much tighter tolerance. Parallelism between the first and second planes is important because it greatly reduces the complexity of software used for coordinating images received from the x-ray line scanner subsystem  32  and the CT scanner subsystem  34 . 
     It should also be noted that the same conveyor belt, namely the conveyor belt  50  of the inspection conveyor apparatus  20 , transports containers while being scanned respectively by the x-ray line scanner subsystem  32  and the CT scanner subsystem  34 . There is thus no transition from one conveyor belt to another between the x-ray line scanner subsystem  32  and the CT scanner subsystem  34 . Because of the use of a single conveyor belt for transporting containers from the x-ray line scanner subsystem  32  to the CT scanner subsystem  34 , the orientation and predictability of positioning of the containers are insured. 
     As will also be evident from the description that follows, many features of the inspection apparatus  8  provide for high speed inspection of containers. The features providing for high speed inspection of containers in combination generally make provision for inspection of at least 600 containers per hour. 
     Radiation Locking 
     The concept of radiation locking is now described by way of an example illustrated in FIG. 3 a  to FIG. 3 j.    
     In the description that follows, the curtain of the first shielding arrangement  24  is referred to as “the first curtain  56 A”, the curtain of the second shielding arrangement  26  is referred to as “the second curtain  56 B” the curtain of the third shielding arrangement  28  is referred to as “the third curtain  56 C”, and the curtain of the fourth shielding arrangement  30  is referred to as “the fourth curtain  56 D”. (Compare FIG. 2 with FIG. 3 a ). 
     In the following discussion of FIG. 3 a  to FIG. 3 j  it can also be inferred that the confines of the inspection tunnel section  14  are continuously radiated, unless specifically stated otherwise. 
     First, as illustrated in FIG. 3 a , a number of dosed containers  60 ,  62  are lined up, utilizing conventional airport conveyor belts, in front of the first curtain  56 A. The first curtain  56 A is raised. The second curtain  56 B remains in a down position so that radiation from the inspection tunnel section  14  is prevented from reaching the loading tunnel section  12 . 
     Next, as illustrated in FIG. 3 b , a first of the containers  60  is moved through the first end of the loading tunnel section  12  into the loading tunnel section  12 . The second curtain  56 B remains in a down position. 
     Next, as illustrated in FIG. 3 c , the first curtain  56 A is lowered, thus “locking” the first container  60  between the first curtain  56 A and the second curtain  56 B and hence the concept of “radiation locking”. Radiation locking merely serves to ensure that the first curtain  56 A is down before the second curtain  56 B is raised and generally lasts only for a fraction of a second. 
     Next, as illustrated in FIG. 3 d , the second curtain  56 B is raised. Although radiation from the inspection tunnel section  14  may enter the loading tunnel section  12 , the radiation is prevented by the first curtain  56 A from leaving the loading tunnel section  12 . 
     It can already be seen from the discussions of FIG. 3 a  to FIG. 3 d  that at least one of the first curtain  56 A and the second curtain  56 B is always in a down position, at least when the confines of the inspection tunnel section  14  are radiated. Radiation is therefore prevented from leaving the inspection apparatus from a container entry side. The controller (see reference numeral  36  in FIG. 2) may be programmed so that the line scanner  32  and the CT scanner subsystem  34  are switched off when, for whatever reason, both the first curtain  56 A and the second curtain  56 B are at least partially open (or when both the first curtain  56 A and the second curtain  56 B are not entirely closed). Sensors may for example be provided which detect the positioning of the curtains  56 A and  56 B and which forward the detected information to the controller. 
     Next, as illustrated in FIG. 3 e , the first container  60  is moved (utilizing the first and second conveyor apparatus  18  and  20 —see FIG. 2) from the loading tunnel section  12  into the inspection tunnel section  14 . 
     Once the first container  60  is located entirely within the inspection tunnel section  14 , the second curtain  56 B is again lowered, as illustrated in FIG. 3 f.    
     Next, as illustrated in FIG. 3 g , the third curtain  56 C is raised and the first container  60  is moved (utilizing the second and third conveyor apparatus  20  and  22 —see FIG. 2) from the inspection tunnel section  14  into the unloading tunnel section  16 . The fourth curtain  56 D remains in a down position so as to prevent radiation, which may enter the unloading tunnel section  16  from the inspection tunnel section  14 , from leaving the inspection apparatus through the second end of the unloading tunnel section  16 . 
     In the meantime, a second of the containers  62  may be moved into the loading tunnel section  12  in a manner as hereinbefore described with reference to FIG. 3 a  to FIG. 3 d . Further movement of the second container  62  is similar to the movement of the first container  60  as hereinbefore and hereinafter described and should further be evident from the drawings. 
     Once the first container  60  is located entirely within the unloading tunnel section  16 , the third curtain  56 C is again lowered, as illustrated in FIG. 3 h . The first container  60  is thus locked between the third curtain  56 C and the fourth curtain  56 D, again illustrating the concept of radiation locking, this time after exit of the first container  60  from the inspection tunnel section  14 . Again, radiation locking of the first container  60  within the unloading tunnel section  16  may last only for a fraction of a second. 
     As with the first and second curtains  56 A and  56 B, at least one of the third curtain  56 C and the fourth curtain  56 D is always in a down position, at least when the confines of the inspection tunnel section  14  are radiated. Radiation is therefore also prevented from leaving the inspection apparatus from a container exit side. The controller (see reference numeral  36  in FIG. 2) may be programmed so that the line scanner  32  and the CT scanner subsystem  34  are switched off when both the third curtain  56 C and the fourth curtain  56 D are at least partially open. Sensors may for example be provided which detect the positioning of the curtains  56 C and  56 D and which forward the detected information to the controller. 
     Next, as illustrated in FIG. 3 i , the fourth curtain  56 D is raised and the first container  60  is moved out of the unloading tunnel section  16  through the second end of the unloading tunnel section  16 . The third curtain  56 C remains in a down position, thus preventing radiation within the inspection tunnel section  14  from reaching the unloading tunnel section  16 . 
     For a complete discussion, FIG. 3 j  illustrates the inspection apparatus after the fourth curtain  56 D is lowered. The second container  62  may at this stage be located within the inspection tunnel section  14 . FIG. 3 j  is thus similar to FIG. 3 f . The above described steps may then be repeated for a third and following containers. 
     It should be evident from the aforegoing description of FIG. 3 a  to FIG. 3 j  that one advantage of the inspection apparatus is that the confines of the inspection tunnel section  14  can be continuously radiated, i.e. without having to turn off a radiation source accompanied by delay in inspection of containers. 
     Continuous Scanning 
     Referring briefly to FIG. 3 e  to FIG. 3 g , the container  60  is scanned while moving into (FIG. 3 e ), while located within (FIG. 3 f ) and while moving out of (FIG. 3 g ) the inspection tunnel section  14 . The manner in which the container  60  is scanned and certain related features are now described with reference to FIG. 4 a  to FIG. 4 c  which correspond to FIG. 3 e  to FIG. 3 g , respectively. 
     In the following description of FIG. 3 e  to FIG. 3 g , detailed aspects relating to software used in the inspection apparatus, are not described in detail since the patents of Peschmann, referenced previously, teaches the general principles and techniques whereby objects of interest, such as explosives hidden in a dosed container, are nonintrusively detected utilizing certain existing x-ray technique-based nonintrusive inspection apparatus. The Peschmann patents teach many details of the general and specific implementation of the present invention wherein the x-ray line scanner may be used to form a convention x-ray projection image, and in which software programs residing in the memory of a computer may be used to analyze the x-ray line scanner images, and to identify locations within a container being scanned that may deserve more detailed x-ray technique-based nonintrusive inspection. Peschmann teaches further that upon identifying such locations in the container, the container may be positioned with respect to the imaging plane of a CT scanner subsystem, such that a sequence of cross-sectional images of the container may be acquired at the locations so specified. Peschman further teaches that additional software programs that may reside in the memory of a computer may be used to analyze the cross-sectional images formed by the CT scanner subsystem, and that additional software programs that may reside in the memory of a computer may analyze all of the data available from both the x-ray line scanner subsystem and the CT scanner subsystem to render decision as to the likely presence of an object of interest such as an explosive hidden in the container. 
     As previously mentioned, the x-ray line scanner subsystem and the CT scanner subsystem (reference numerals  32  and  34  in FIG. 2) are located relatively close to one another. In addition to such a set of general and specific details of implementation provided by the Peschman patents, the present invention now provides particular scanning methods that enable the inspection apparatus  8  to be designed more compactly by permitting imaging planes of the x-ray line scanner subsystem and the CT scanner subsystem to be located closer to one another than would be otherwise possible, while still being capable of achieving a high rate of inspection of containers. What should be understood, however, is that the controller (reference numeral  36  in FIG. 2) is programmed to carry out the steps illustrated in FIG. 4 a (i) to FIG. 4 c (ii). 
     Referring to FIG. 4 a (i), the container  60  is illustrated as it passes from the loading tunnel section  12  into the inspection tunnel section  14 . An imaging plane of the x-ray line scanner subsystem is represented by the line  32  and an imaging plane of the CT scanner subsystem is represented by the line  34 . The imaging plane  32  of the x-ray line scanner subsystem may be spaced from the second curtain  56 B by a distance which is less than the length of the container  60  so that the container  60  starts moving to the imaging plane  32  of the x-ray line scanner subsystem before being entirely located within the inspection tunnel section  14 . 
     FIG. 4 a (ii) is a view of the container  60 , illustrating the container  60  after a first front portion  70  has been moved past the imaging plane  32  of the x-ray line scanning subsystem. Inspection software analyzing the image formed by the x-ray line scanning subsystem represents the first front portion  70  of the container  60 , and may at this stage detect a location  72 A within the first front portion  70  which may contain an object of interest  72 B. Alternatively, the inspection software may determine, based on other rules, that the specific location  72 A within the first front portion  70  of the container  60  requires further measurements by the CT scanner subsystem. 
     Acquisition of the x-ray line scanner image continues whenever the container progresses past the imaging plane  32  of the x-ray line scanner subsystem. This image acquisition does not necessarily require the container to move continuously, nor does it necessarily require the container to move at a constant speed or in a single direction. 
     Once the location  72 A has been identified, the speed at which the container  60  moves may then be progressively reduced and the container  60  may be brought to a standstill, as illustrated in FIG. 4 b (i) and FIG. 4 b (ii), with the location of interest  72 A located in the imaging plane  34  of the CT scanner subsystem. Movement of the container  60  and acquisition of the x-ray line scanner image is thus position dependent as opposed to, for example, time dependent. Once the container  60  has stopped, the CT scanner subsystem  34  may scan the location of interest  72 A. 
     In the time between identifying the location of interest  72 A and the time at which the container is stopped with the location of interest  72 A within the imaging plane  34  of the CT scanner subsystem, the x-ray line scanner subsystem may scan a second front portion  74  for of the container  60 . A second object of interest  76  may be detected by the x-ray line scanner subsystem  32 . Note that the imaging plane  32  of the x-ray line scanner subsystem and imaging plane  34  of the CT scanner subsystem may be spaced from one another by a distance which is less than the overall length of the container  60  so that the container  60  passes through the imaging plane  34  of the CT scanner subsystem before a rear portion  78  of the container  60  passes through the x-ray line scanning plane  32 . 
     The container  60  may then be advanced until the second object of interest  76  is located in the imaging plane  34  of the CT scanner subsystem, as illustrated in FIG. 4 c (i) and FIG. 4 c (ii). The imaging plane  34  of the CT scanner subsystem may be spaced from the third curtain  56 C by a distance which is less than the overall length of the container  60  so that the container  60  is already partially located within the unloading tunnel section  16 . In the meantime, the x-ray line scanner subsystem  32  may scan the rear portion  78  of the container  60 . 
     Note that the container  60  may therefore be moved through the inspection tunnel section  14  without altering the direction of movement of the container  60  relative to the x-ray line scanner subsystem  32  and the CT scanner subsystem  34 . 
     Because the first curtain  56 B, the imaging plane  32  of the x-ray line scanner subsystem, the imaging plane  34  of the CT scanner subsystem, and the third curtain  56 C are spaced from one another by relatively small distances, the overall length of the inspection tunnel section  14  is relatively short. In one example the imaging plane  32  of the x-ray scanner subsystem is spaced from the first curtain  56 B by a distance of about 34 centimeters, the imaging plane  34  of the CT scanner subsystem is spaced from the imaging plane  32  of the x-ray line scanner subsystem by a distance of about 87 centimeters, the third curtain  56 C is spaced from imaging plane  34  of the CT scanner subsystem by a distance of about 65 centimeters, and the overall length of the inspection tunnel section  14  is therefore about 186 centimeters. 
     Structural Integrity 
     FIG. 5 is a perspective view illustrating only the support frame  10  and the CT scanner subsystem  34 . The base frame  38  is of monocoque design. Monocoque designs are frequently used, for example, in the design of the hulls of ships and in the design of the bodies of aircraft. In the present example, the base frame  38  generally has the shape of the hull of a ship in that the base frame  38  generally has a channel shape. Other components also form part of the base frame  38  which are similar to a bulkhead of a ship. 
     More specifically, the base frame  38  includes a first monocoque section  82 , a second monocoque section  84 , and a third monocoque section  86 . It should be understood that the first monocoque section  82  is located in the region of the loading tunnel section, the second monocoque section  84  is located in the region of the inspection tunnel section, and the third monocoque section  86  is located in the region of the unloading tunnel section. (See reference numerals  12 ,  14  and  16  in FIG.  2 ). 
     The second monocoque section  84  has a base plate  88 , first and second side walls  90  and  91  respectively, and first and second end walls  92  and  93  respectively. The side walls  90  and  91  are secured to the base plate  88  and extend upwardly from the base plate  88  and away from one another so that the base plate  88  and the first and second side walls  90  and  91  jointly define a channel shape which is wider at the top than at the bottom, similar to the hull of a ship when viewed in cross section. The end walls  92  and  93  are secured at spaced locations within the channel shape defined by the base plate  88  and the side walls  90  and  91 , with edges of the end walls  92  and  93  secured to the base plate  88  and the side walls  90  and  91 . Each end wall  93  or  94  is similar to a bulkhead of a ship. The channel shape of the second monocoque section  84  is extremely resistant to bending, and the channel shape together with the end walls  93  and  94  also provide torsional resistance to the second monocoque section  84 . 
     Further components may be provided which give added support to the base frame  38 . For example, a horizontal deck  95  may be secured to upper edges of the side walls  90  and  91  and the end wall  93 , between the end wall  93  and the CT scanner subsystem  34 . An additional vertical component  96  may be located on a side of the deck opposing the end wall  93  and have an upper edge secured to the deck, side edges secured to the side walls  90  and  91 , and a bottom edge secured to the base plate  88 . The deck and the additional vertical component are preferably located in the region of the arch  40  to provide additional rigidity to the base frame  38  in that region. 
     The first and third monocoque section  82  and  86  are similar to one another in design. Only the first monocoque section  82  is further described. It should however be understood that the description of the first monocoque section  82  that follows may also hold true for the third monocoque section  86 . 
     The first monocoque section  82  has a base plate  97 , first and second side walls  98  and  100 , and an end wall  102 . The side walls  98  and  100  are secured to the base plate  97  and extend upwardly from the base plate  97  and away from one another so that the base plate  97  and the first and second side walls  98  and  100  jointly define a channel shape which is wider at the top and at the bottom. The base plate  97  and the side walls  98  and  100  are positioned against the side walls  90  and  91  of the second monocoque section  84  and secured thereto. The end wall  102  is secured within the channel shape defined by the base plate  97  and the side walls  98  and  100  and on a side thereof opposing the end wall  93  of the second monocoque section  84 . The channel shape of the first monocoque section  82  provides the first monocoque section  82  with resistance to bending and the end walls  93  and  102 , together with the channel shape, provide torsional resistance to the first monocoque section  82 . 
     The arch  40  has opposing ends  104  and  106  which are secured to the side walls  90  and  91 , respectively, of the second monocoque section  84 . A bearing (not shown) is located within the arch  40  and the CT scanner subsystem  34  is mounted to a rotational portion of the bearing. 
     In use, the CT scanner subsystem  34  may rotate at a rate of about 120 revolutions per minute. Furthermore, it may be required that the CT scanner subsystem  34  be relatively large. One reason for the size requirement of the CT scanner subsystem  34  is so that larger containers may pass through the CT scanner subsystem  34 . The CT scanner subsystem  34  may, for example define an opening  110  which is about 113 centimeters in diameter. 
     Another reason for the size requirement of the CT scanner subsystem  34  deals with the compatibility of the inspection apparatus with conveyor belts found within airports. Airport conveyor belts are typically about one meter wide. If the conveyor belts used within the inspection apparatus are less than one meter wide, additional channeling devices may have to be provided to reorient and channel containers from the airport conveyor belts to the conveyor belt of the loading tunnel section. (See reference numerals  50  and  12  in FIG.  2 ). For example, containers may be oriented on the airport conveyor belts so as to be oriented such that their longest the dimension lies transverse to the direction of motion of the conveyor belts. With smaller aperture apparatus, channeling devices may then have to be located between the airport conveyor belts and the inspection apparatus to reorient the containers so that their longest dimensions line up in a direction which is more or less parallel to the direction of motion of the conveyor belts so that the containers fit into the inspection apparatus and onto the conveyor belts used in the inspection apparatus. Such channeling devices may add to the overall length of the inspection apparatus and are preferably avoided. The conveyor belts used within the inspection apparatus  8  are therefore preferably about one meter wide, which means that a one-meter wide conveyor belt should be able to pass through the CT scanner subsystem  34 . 
     However, the relatively large diameter of the CT scanner, together with its high rotational rate, may cause very strong forces to be applied to the base frame  38 . The forces may occur inadvertently due to an unbalanced operating condition arising from any cause. Furthermore, the relatively large diameter of the CT scanner subsystem together with a requirement to accelerate quickly to a high rate of revolution, or decelerate quickly, may cause very strong torsional forces on the base frame  38  when rotation of the CT scanner subsystem  34  is started or stopped. It should be evident from the aforegoing description that the base frame  38  is designed to deal with the high forces which may tend to bend or induce vibration in the base frame  38  when the CT scanner subsystem  34  is in an unbalanced condition, for example, and resist the relatively high torsional forces which act on the base frame  38  when rotation of the CT scanner subsystem  34  is started or stopped. 
     It should be evident from the aforegoing description that the design of the base frame  38  is related to the width of the conveyor belts that are used within the inspection apparatus and that the conveyor belts may be sufficiently wide so that reorienting of containers may be avoided. The containers may thus enter the inspection apparatus while being oriented with their longest dimensions transverse to the direction of motion of the conveyor belts. Because the containers may be oriented in such a manner, a container may therefore be oriented so that the width of the container may be located in a direction approximately parallel to the direction of motion of the conveyor belts, thus potentially permitting container inspection to be completed with a smaller number of CT scanning slices than would be required to complete an equally effective inspection were the container to be oriented differently. 
     Radiation Containment 
     FIG. 6 illustrates a portion of the arch  40 , the inspection tunnel section  14 , the x-ray line scanner subsystem  32 , and the CT scanner subsystem  34 . The inspection tunnel section  14  includes a first tunnel portion  120 , a second tunnel portion  122 , and a third tunnel portion  124  which are all nonrotatably mounted to the base frame. (See reference numeral  38  in FIG.  2 ). 
     The first tunnel portion  120  is located on a side of the x-ray line scanner subsystem  32  opposing the CT scanner subsystem  34  and has a first end  126  which is also the first end  42  of the inspection tunnel section  14 , and a second end  128 , opposing the first end  126 , against the x-ray line scanner subsystem  32 . 
     The second tunnel portion  122  is located between the x-ray line scanner subsystem  32  and the CT scanner subsystem  34  and has a first end  130  against the x-ray line scanner subsystem  32 , and a second end  132 , opposing the first end  130 , at the CT scanner subsystem  34 . 
     The third tunnel portion  124  is located on a side of the CT scanner subsystem  34  opposing the x-ray line scanner subsystem  32  and has a first end  134  at the CT scanner subsystem  34  and a second end  136 , opposing the first end  134 , which is also the second end  44  of the inspection tunnel section  14 . 
     The x-ray line scanner subsystem  32  is nonrotatably mounted to the arch  40  and includes a partial gantry enclosure  138  and a radiation tube  140 . Other features of the x-ray line scanner subsystem  32  are similar to those of the CT scanner subsystem  34  and the CT scanner subsystem  34  is described in more detail hereinbelow. 
     The arch  40  is located around the second tunnel portion  122  and defines a bearing housing  142  around the second tunnel portion  122 . The bearing housing  142  is open towards the CT scanner subsystem  34 . A bearing  144  is located within the bearing housing  142 . The CT scanner subsystem  34  includes a gantry enclosure  148 , an x-ray tube  150  which is secured to the gantry enclosure  148 , and a ring  152  which is secured to the gantry enclosure  148 . The ring  152  extends into the bearing housing  142  and is located on a rotating portion of the bearing  144 , thus mounting the CT scanner subsystem  34  rotatably to the arch  40 . The CT scanner subsystem  34  rotates around the inspection tunnel section  14 . 
     FIG. 7 illustrates the gantry enclosure  148  and the ring  152  of the CT scanner subsystem  34  in more detail. 
     The gantry enclosure  148  includes first and second spaced gantry plates,  154  and  156  respectively, first, second, and third spacers  158 ,  160 , and  162  respectively, a collimator face  164 , and a hollow, substantially frustum pyramidal collimator component  165 . 
     The first gantry plate  154  has a gantry aperture  166  formed therein and the second gantry plate  156  also has a gantry aperture  168  formed therein. The ring  152  is mounted to the first gantry plate  154  around the gantry aperture  166  in the first gantry plate  154 . 
     The collimator face  164  is curved and a hole  170  is formed in the collimator face  164 . The collimator component  165  has a base  172  which is slightly larger than the hole  170  in the collimator face  164 . The collimator component  165  also has an apex  174  which is smaller than the base  172  and which is formed so as to fit snugly against the x-ray tube. (See reference numeral  150  in FIG.  6 ). When the base  172  of the collimator component  165  is positioned over the hole  170  and the collimator component  165  is mounted to the collimator face  164 , the hole  170  may only be accessed through the apex  174  of the collimator component  165 . 
     The first and second gantry plates  154  and  156  are secured to the spacers  158 ,  160 , and  162 , with the spacers being located between the gantry plates and around the gantry apertures  166  and  168 . The first and second spacers  158  and  160  may be made of a material such as aluminum. The third spacer  162  has a curved shape and may also be made of a material such as aluminum. 
     The collimator face  164  may also be made of a material such as aluminum and is shorter than the third spacer  162 . 
     The spacers  158 ,  160 , and  162  and the collimator face  164  are positioned in a trapezium-like shape with the third spacer  162  and the collimator face  164  respectively forming a long side and a short side of the trapezium and the first and second spacers  158  and  160  connecting edges of the third spacer  162  and the collimator face  164  so that the first and second spacers  158  and  160  are spaced closer to one another at the collimator face  164  and further from one another at the third spacer  162 . 
     The gantry enclosure  148  is so partially defined by the first and second gantry plates  154  and  156 , the spacers  158 ,  160 , and  162 , and the collimator face  164 . The only areas of the gantry enclosure  148  which are open are due to the gantry apertures  166  and  168  in the first and second gantry plates  154  and  156  respectively, and due to the hole  170  in the collimator face  164 . 
     The gantry enclosure  148  includes lead lining which prevents radiation from escaping from the gantry enclosure  148 . Lead tiles  176  are mounted to the third spacer  162  within the gantry enclosure  148 . Lead plates  178 ,  180  are also secured to the first spacer  158  and the second spacer  160 , respectively, within the gantry enclosure  148 , and a lead plate  182  is secured to the collimator face externally of the gantry enclosure  148 . A lead liner  184  is also secured to the first gantry plate  154  on a side thereof facing into the gantry enclosure  148 , and another lead liner  186  is secured to the second gantry plate  156  on a side thereof facing into the gantry enclosure  148 . The lead liners  184  and  186  conform to the internal dimensions of the gantry enclosure  148 . In addition, the collimator component  165  is made of the lead. It can thus be seen that the entire gantry enclosure  148  is lead lined and thus resistant to transmission of x-ray radiation. The only areas through which x-ray radiation may pass into or out of the gantry enclosure  148  are the apex  174  of the collimator component  165  and the gantry apertures  166  and  168  in the first and second gantry plates  154  and  156 , respectively. 
     Referring again to FIG. 6, the x-ray tube  150  fits snugly on the apex  174  of the collimator component  165 . A lead lining  188  covers all inner surfaces of the x-ray tube  150 , except an area of the x-ray tube  150  directly over the apex  174  of the collimator component  165 . The entire area including the x-ray tube  150  and the collimator component  174  is thus enclosed by lead. It should now the evident that, when the x-ray tube  150  is activated, x-rays are transmitted from the x-ray tube  150  through the collimator component  165  into the confines of the gantry enclosure  148 . X-ray radiation may only escape through the gantry apertures  166  and  168  in the first and second gantry plates  154  and  156  respectively. 
     Detector arrays  190  are located within the gantry enclosure  148  on a side of the gantry enclosure  148  opposing the x-ray tube  150 . The detector arrays  190  may for example be mounted to the lead tiles  176 . Conductors  192  are connected to the detector arrays  190  and extend through the lead tiles  176  and the third spacer  162  so as to provide an electrical connection between the detector arrays  190  and externally of the gantry enclosure  148 . 
     The x-ray line scanner subsystem  32  may have a similar construction to the CT scanner subsystem  34  and is lead lined in a manner similar to the CT scanner subsystem  34 . 
     Lead linings  196 ,  198  and  200  are also formed on the internal dimensions of the first, second and third tunnel portions  120 ,  122  and  124 , respectively. Lead linings  196  and  198  of the first and second tunnel portions  120  and  122  are sufficiently close and overlapping the lead linings of the x-ray line scanner subsystem  32  so that interfaces between the x-ray line scanner subsystem  32  and the first and second tunnel portions  120  and  122  are, in a radiation sense, substantially sealed. 
     The second end  132  of the (stationary) second tunnel portion  122  extends into the gantry aperture  166  in the first gantry plate  154  of the (rotatable) CT scanner subsystem  34 . The lead lining  198  on the second tunnel portion  122  is located relatively dose and overlapping the lead liner  184  on the first gantry plate  154  and is separated therefrom only by a gap which is necessary to allow for rotation of the CT scanner subsystem  34  relative to the second tunnel portion  122 . And interface between the second tunnel portion  122  and the CT scanner subsystem  34  is thus, in a radiation sense, substantially sealed. 
     Similarly, the first end  134  of the third tunnel portion  124  extends into the gantry aperture  168  of the second gantry plate  156 , and the lead lining  200  is located relatively close to the lead liner  186  so that an interface between the third tunnel portion  124  and the second gantry plate  156  is, in a radiation sense, substantially sealed. 
     Referring again to FIG. 2, the internal dimensions of the loading and unloading tunnel sections  12  and  16  are also lead lined. Each curtain  56  is made of a number of layers which are located over one another, including a number of layers containing significant amounts of lead. 
     It should be evident that the entire inspection apparatus  8  is self shielded against in the sense that it effectively attenuates leaking of radiation therefrom and that no extraneous radiation resistant shielding members have to be provided for purposes of radiation containment. Because no extraneous radiation shielding members have to be provided, much less lead lining is required—see for example how the x-ray tube  150  is lead lined with the minimal amount of lead. 
     The lead on the CT scanner subsystem  34  does make it somewhat heavier, with corresponding consequences as far as stresses and strains on the base frame are concerned. (See reference numerals  38  in FIG.  5 ). The base frame is, as described with reference to FIG. 5, however designed to deal with relatively large forces. 
     Although self shielding has been specifically described with reference to an x-ray technique-based nonintrusive inspection apparatus for inspection of containers, the principles of self shielding may also find application in related technologies such as CT scanning of people and other patients. A self shielded CT scanner may be located within a room and be used for inspecting and diagnosing of a patient. Since the CT scanner is self shielded, the patient may be inspected, utilizing the CT scanner, while people are located around the CT scanner within the same room. Furthermore, such self-shielded apparatus would obviate the need and cost of providing special rooms with walls, floors, and ceilings which are capable of providing such radiation shielding 
     Driving Arrangement 
     FIG. 8 illustrates in end view the CT scanner subsystem  34  and a driving arrangement  210  forming part of the x-ray technique-based nonintrusive inspection apparatus and which is used for rotating the CT scanner subsystem  34 . 
     It should be evident from the aforegoing description that the CT scanner subsystem  34  is rotatably mounted to the arch of the support frame. (See for example reference numerals  10  and  40  in FIG.  2  and FIG.  5 ). The CT scanner subsystem  34  has a circular outer surface  212  which may, for example, be on a ring which may be secured to the gantry enclosure. (See reference numeral  148  in FIG.  6 ). 
     The driving arrangement  210  includes first, second and third pulleys  214 ,  216  and  218 , respectively, an electric motor  220 , and a flexible member  222 , such as a flexible belt or a chain, forming a closed loop. The pulleys  214 ,  216  and  218  are located at various locations around the C.T. scanner subsystem  34 . The first and second pulleys  214  and  216  are rotatably mounted to the support frame. (See reference numeral  10  in FIG.  2 ). The electric motor  220  is also mounted to the support frame and the third pulley  218  is directly coupled and mounted to a shaft of the electric motor  220  so as to be rotated by the electric motor  220  when the electric motor  220  is operated. 
     The flexible member  222  encircles and runs over the first, second and third pulleys  214 ,  216  and  218 , respectively. When stationary, or at any given moment while moving over the pulleys  214 ,  216 , and  218 , the flexible member  222  has a first section  224  running from the first pulley  214  to the second pulley  216  in a first direction  226  around and over the circular outer surface  212 . The flexible member  222  also has a second section  228  returning from the second pulley  216  over the third pulley  218  back to the first pulley  214  in a second direction  230 , which is opposite to the first direction  226 , around the circular outer surface  212 . 
     In use, when the third pulley  218  is rotated by the electric motor  220 , the flexible member  222  progresses over the pulleys  214 ,  216  and  218 , for example in an anti-clockwise direction. Because of progression of the flexible member  222 , the CT scanner subsystem  34  is rotated in a clockwise direction 
     It can thus the seen that a complete revolution of the flexible member  222  does not entirely encircle the CT scanner subsystem  34 . Because of the positioning of the flexible member  222 , it may be engaged with the circular outer surface  212  without having to be positioned so that it surrounds the CT scanner subsystem  34 , the inspection tunnel section, or the inspection conveyor apparatus. The flexible member  222  may thus be installed without obstruction from the CT scanner subsystem  34  itself or obstruction from the inspection tunnel section of the inspection conveyor apparatus which are mounted to the base portion in the vicinity of the CT scanner subsystem  34 . (See reference numerals  14 ,  20  and  38  in FIG.  1 ). Maintenance due to failure of the flexible member  222  is thus greatly simplified. 
     In other embodiments more pulleys may be used serving various purposes such as tensioning of the flexible member  222 , or the flexible member  222  may be driven by a separate device. 
     Shielding Arrangements 
     FIG. 9 illustrates one of the shielding arrangements  24 ,  26 ,  28  or  30  of FIG. 2 in more detail. The shielding arrangement  24 ,  26 ,  28  or  30  forms part of a larger shielding apparatus which includes support structures  240  which are mounted to the base frame and which form part of the support frame of the x-ray technique-based nonintrusive inspection apparatus of the invention. (See reference numerals  8 ,  10  and  38  in FIG.  2 ). 
     Each shielding arrangement  24 ,  26 ,  28  or  30  includes, in addition to the curtain roller  54  and the radiation resistant curtain  56 , also an electric motor  242 , a tensioning roller  244 , a flexible sheet  246 , and a torsion spring  248 . 
     The curtain roller  54  is rotatably mounted between the support structures  240 , and the curtain  56 , as previously mentioned, is secured to the curtain roller  54  so as to be rolled onto or from the curtain roller  54  upon rotation of the curtain roller  54 . 
     The electric motor  242  is also secured to one of the support structures  240 . A driving belt  250  couples the electric motor  242  to the curtain roller  54  so that the curtain roller  54  is rotated upon operation of the electric motor  242 . The rotational positioning of the curtain roller  54 , and therefore also the height of the curtain  56 , is also determined by the electric motor  242 . 
     The sheet  246  has one portion attached to the curtain roller  54  and a second portion attached to the tensioning roller  244 . The sheet  246  is rolled onto the tensioning roller  244 . 
     The tensioning roller  244  is also rotatably mounted between the support structures  240 . The torsion spring  248  is located between one of the support structures  240  and that tensioning roller  244 . The torsion spring  248  is under torsion, i.e. the torsion spring  248  is torsionally biased, thus tending to rotate the tensioning roller  244 . The tensioning roller  244  is, however, prevented from rotating because the tensioning roller  244  is connected by the sheet  246  to the curtain roller  54  and the rotational position of the curtain roller  54  is determined by the electric motor  242 . It should thus be evident that the sheet  246  is under tension between the curtain roller  54  and the tensioning roller  244  because of the tendency of the tensioning roller  244  to rotate and the predetermined rotational positioning of the curtain roller  54 . 
     FIG. 10 illustrates the arrangement of FIG. 9 in end view. The curtain  56  hangs from one side of the curtain roller  54 . The tensioning roller  244  is located on the same side of the curtain roller  54  as the side of the curtain roller  54  from which the curtain  56  hangs, with the curtain  56  being located between the curtain roller  54  and the tensioning roller  244 . 
     The sheet  246  passes from under the tensioning roller  244  over and onto the curtain roller  54 . The sheet  246  therefore extends clockwise around the tensioning roller  244  and anti-clockwise around a portion of the curtain roller  54 . 
     The tensioning roller  244  has a tendency to rotate in an anti-clockwise direction  251 . Because of the tendency of the tensioning roller  244  to rotate in an anti-clockwise direction, and the connection between the tensioning roller  244  and the curtain roller  54 , the curtain roller has a tendency to rotate in a clockwise direction. Rotation of the curtain roller  54  in an anti-clockwise direction results in rolling of the curtain  56  onto the curtain roller  54  and rotation of the curtain roller  54  in a clockwise direction results in rolling of the curtain  56  from the curtain roller  54 . The tensioning roller  244  thus tends to roll the curtain  56  from the curtain roller  54 . 
     The tensioning roller  244  and the sheet  246  ensure that the curtain  56  is rolled tightly and in a controlled manner onto the curtain roller  54 . The tensioning roller  244  and the sheet  246  also ensure that the curtain  56  remains tightly on the curtain roller  54  when rotation of the curtain roller  54  in an anti-clockwise direction is decelerated. The tensioning roller  244  and the sheet  246  also ensure that the curtain  56  remains tightly on the curtain roller  54  when the curtain roller  54  is rotated in a clockwise direction. 
     For example, FIG. 11 illustrates the arrangement of FIG. 10 when the curtain  56  is rolled onto the curtain roller  54  by rotation of the curtain roller  54  in an anti-clockwise direction  252 . The sheet  246  is rolled together with the curtain  56  onto the curtain roller  54  with the sheet  246  being located on an outer surface of the curtain  56 . Due to the tension present in the sheet  246 , the sheet  246  creates a force  254  on the curtain  56  which is radially inward towards the curtain roller  54 . Because of the force  254 , the curtain  56  is maintained in dose contact with the curtain roller  54  and preceding layers of the curtain  56  when the curtain  56  is rolled onto the curtain roller  54 . 
     When the curtain roller  54  is rotated in an anti-clockwise direction, the curtain  56  has momentum. When the curtain roller  54  is brought to a halt, after being rotated in an anti-clockwise direction, the momentum of the curtain  56  will tend to lift the curtain  56  from the curtain roller  54  or preceding layers of the curtain  56  on the curtain roller  54 . The tendency of the curtain  56  to lift is, however, counteracted by the force  254 . 
     When the curtain roller  54  is accelerated in a clockwise direction, lack of momentum of the curtain  56  will attend tend to cause the curtain  56  to lift, which tendency is again counteracted by the force  254 . 
     By correctly positioning the tensioning roller  244 , the trajectory of the curtain  56  when it rolls off the curtain roller  54  can also be controlled. The trajectory of the curtain  56  is preferably substantially vertically downwardly. Vertical downward movement of the curtain  56  is preferred because waves within the curtain  56  or whiplash-like oscillations of the curtain  56  can so be avoided and the curtain  56  can thus the brought to standstill much quicker. 
     Referring again to FIG. 10, it should also be noted that the curtain roller  54  has an outer surface which has a shape which is generally in the form of a spiral having a step  260 . An end of the curtain  56  is secured to an inner portion  262  of the spiral with a edge of the curtain  56  adjacent the step  260 . A surface  264  of the curtain  56  opposing the inner portion  262  is substantially in line with an outer portion  266  of the spiral. 
     When the curtain  56  is rolled onto the curtain roller  54 , as illustrated in FIG. 10, up to the point where the curtain  56  starts rolling onto itself (the sheet  246  being located between layers of the curtain  56 ) a smooth transition is ensured. A smooth transition is important because waves within or whiplash-like oscillations of the curtain  56  may be avoided, and the power demanded of the drive motor is made more uniform in time. When the curtain  56  is rolled from the curtain roller  54  a smooth transition is also ensured which, in addition to the positioning of the tensioning roller  244 , further prevents waves within or whiplash-like oscillations of the curtain  56 . 
     It can thus be seen from the aforegoing description that the curtain  56  may be lowered and raised quickly and in a controlled manner both because of the tensioning roller  244  and the spiral shape of the curtain roller  54 . 
     Detector Array Collimators 
     FIG. 12 a (i) to FIG. 12 c (ii) illustrate a method of making a collimator for a detector array of the CT scanner. (See reference numeral  34  in FIG.  2 ). 
     FIG. 12 a (i) illustrates a die  310  which may be used for injection molding of such a body of a collimator. The die  310  includes a cup  312  and a shape defining element  314 . The shape defining element  314  includes a substructure  316  and a plurality of fins  318  which are secured to the substructure  316 . The fins  318  define a plurality of septa gaps  320  between them. 
     Referring to FIG. 12 a (ii), the shape defining element  314  also includes delimiting portions  322  secured to the substructure  316  on opposing sides of the fins  318 . The fins  318  are slightly longer than the delimiting portions  322 . 
     FIG. 12 b (i) illustrates the die  310  after the shape defining element  314  is inserted into the cup  312 . The fins  318  extend all the way to a base of the cup  312 . 
     In FIG. 12 b (ii) it can be seen that L-shaped support structure gaps  324  are formed between opposing surfaces of the fins  318  and the delimiting portions  322 , and between the delimiting portions  322  and the base of the cup  312 . In another section through FIG. 12 b (i), one will be able to see that the support structure gaps  324  and the septa gaps  320  are in communication with one another. 
     A material is injected into one of the support structure gaps  324  so that the material fills the support structure gaps  324  and the septa gaps  320 . The material preferably comprises about 86 percent lead, 3 percent tin, and 11 percent antimony. The lead provides the material with x-ray radiation shielding capabilities, while the purpose of the alloy between the elements is to provide the material with the strength that lead, by itself, lacks. 
     The material is then allowed to set within the die  310  to form a body of a collimator which is then removed from the die  310  as will be further described hereinbelow with reference to FIG.  14 . FIG. 12 c (i) illustrates the body  330  of the collimator  332 . The body  330  has a plurality of septa  334 , formed in the septa gaps  320 , which are located next to one another. 
     Referring to FIG. 12 c (ii), it can be seen that support structures  336  are formed within the support structure gaps  324  and that the septa  334  are secured between and supported by the support structures  336 . The support structures  336  include mounting portions  338  which are coplanar with one another, and walls  340  extending from the mounting portions  338  parallel to one another. 
     FIG. 13 is a perspective view of the collimator  332 . Registration notches  341  are formed within sides of the mounting portions  338 . The registration notches  341  allow for positioning and securing of a plurality of collimators such as the collimator  332  simply, reliably, and accurately in a modular fashion. 
     It can be seen from the aforegoing description that an effective and easy method is provided for forming the body  330  of the collimator  332 . 
     More importantly, the body  330  has superior strength characteristics because of the materials used for forming the body and because of the manner in which the septa  334  are secured between the support structures  336 . The collimator  332  may be located on a detector array of the CT scanner subsystem (see reference numeral  34  in FIG. 2) wherein the detector array rotates at a relatively large radius. The CT scanner subsystem may, in addition, rotate at a relatively high rate of revolution. The radius of rotation of the detector array, together with the relatively high rate of revolution of the CT scanner subsystem may cause large centrifugal forces to act on the collimator  332 . The strength characteristics of the body  330  of the collimator  332  are thus important for dealing with the centrifugal forces. 
     FIG. 14 illustrates in much exaggerated detail an x-ray tube  150  which is used in the CT scanner subsystem (see reference numeral  150  in FIG.  6 ), and a view of the septa  334  when the collimator  332  of FIG.  12  and FIG. 13 is installed on a detector array (not shown). 
     Each septum  334  has first and second opposed surfaces  342  and  344 , respectively, and a center line  346  between the surfaces  342  and  344 . The center lines  346  converge towards one another in a direction  348  and meet at the x-ray tube  150 . Because of the orientations of the center lines  346  relative to one another, x-rays  350  which are emitted by the x-ray tube  150  may pass through collimator apertures  352  between the septa  334  in a manner wherein the x-rays  350  are correctly collimated. 
     Surfaces  342  and  344  of two of the septa  334  which face one another do, however, not converge in the direction  348 . As shown in the drawing, it may be possible that the opposing surfaces  342  and  344  of two of the septa  334  located next to one another may diverge from one another in the direction  348 . The reason for the orientations of the opposing surfaces  342  and  344  relative to one another is so that the fins (see reference numeral  318  in FIG. 12 b (i)), when the septa  334  are manufactured, may be removed. Each fin will therefore have opposing surfaces which are substantially parallel to one another or which taper towards one another in a direction from the substructure (see reference numeral  316  in FIG. 12 a (i)) towards tips of the fins. 
     As mentioned, FIG. 14 is in greatly exaggerated detail. The angles between the center lines  346  of the septa  334  are, in practice, much smaller than indicated in FIG.  14 . Removal of the fins is therefore not substantially hampered because of the angles of the center lines  346  relative to one another. In practice, for example, sixteen of the septa  334  may be provided, a lower tip of a first of the septa may be spaced from a lower tip of a sixteenth of the septa by a distance of about 50 millimeters, and an upper tip of the first septum may be spaced from an upper tip of the sixteenth septum by a distance of about 49 millimeters. 
     Container Jam Release 
     FIG. 15 illustrates one of the conveyor apparatus  18  or  22  and its interaction with the base frame  38 . (Compare FIG. 15 with FIG.  2 ). 
     Rails  410  are located on opposing sides of the base frame  38 . A lever  412  is pivotally mounted to a portion  414  of the base frame  38 . Handles  416  are mounted to ends of the lever  412 . A pin  418  is secured to the lever  412  intermediate a pivot axis  420  of the lever  412  and one of the handles  416 . 
     The conveyor apparatus  18  or  22 , in addition to the front conveyor roller  46 , the rear conveyor roller  48 , and the conveyor belt  50  (compare with FIG.  2 ), further includes a conveyor slider plate  424  and a number of bracket assemblies  426 . The bracket assemblies  426  are mounted directly to the conveyor slider plate  424  and the front and rear conveyor rollers  46  and  48  are, in turn, rotatably mounted between respective sets of the bracket assemblies  426 . 
     The conveyor apparatus  18  or  22  as shown in FIG. 15 may be preassembled by a subcontractor. The subcontractor may also tension the conveyor belt  50  of the conveyor apparatus  18  or  22  before the conveyor apparatus  18  or  22  is supplied to another entity which mounts the conveyor apparatus  18  or  22  to the base frame  38 . 
     A slot  428  is formed through the conveyor slider plate  424 . The slot  428  extends in a direction transverse to the direction of motion of the conveyor belt  50 , and therefore substantially parallel to the front and rear conveyor rollers  46  and  48 . 
     The arrows  430  indicate mounting of the conveyor apparatus  18  or  22  onto the base frame  38 . The conveyor slider plate  424  nestles between and on the rails  410  so as to be movable only in a direction  432  in which the rails  410  extend. The pin  418  is aligned with the slot  428  so that the pin  418  extends through the slot  428  when the conveyor slider plate  424  is located on the rails  410 . 
     An operator may move one of the handles  416  so that the lever  412  rotates about the pivot axis  420 . Rotation of lever  412  causes rotation of the pin  418  about the pivot axis  420 . The pin  418  engages within the slot  428  within the conveyor slider plate  424  so that the conveyor apparatus  18  or  22  is moved backward or forward along the rails  410 . The pin  418  also slides along the slot  428  when the lever  412  is rotated. Movement of the pin  418  along the slot  428  is limited by the length and positioning of the slot  428  so that movement of the conveyor apparatus  18  or  22  along the rails  410  is also limited. 
     Although only one of the conveyor apparatus  18  or  22  is shown in FIG. 15, it should be understood that both of the conveyor apparatus  18  and  22 , as shown in FIG. 2, have a design similar to that shown in FIG.  15 . The conveyor apparatus  20  is rigidly mounted to the base frame  38 , so that only the conveyor apparatus  18  and  22  are able to be moved by moving its respective lever  412 . 
     In use, the conveyor apparatus  18 ,  20  and  22  are mounted to the rails  410  in such a manner that adjacent front and rear rollers  46  and  48  thereof are located fairly close to one another. By so locating the conveyor apparatus  18 ,  20  and  22  relative to one another, smooth transition of containers from one conveyor apparatus to another is ensured. It may, however, happen from time to time that parts of containers, such as belts on luggage, become jammed between adjacent ones of the front and rear conveyor rollers  46  and  48  of two of the conveyor apparatus which are located sequentially one after the other. One of the conveyor apparatus  18  or  22  may then be moved away from the conveyor apparatus  20  by moving the handle  416  thereof, so as to part adjacent ones of the front and rear conveyor rollers  46  and  48  of the two conveyor apparatus. The jammed parts of containers can then be released from between the adjacent conveyor apparatus. 
     Ideally, the conveyor apparatus  18  or  22  should not, under normal operating conditions, be able to float freely on the rails  410 . An additional mechanism may be provided which may lock the lever  412  releasably into a number of predetermined positions. Other mechanisms may also be provided for controlling movement of the conveyor slider plate  424  along the rails  410 , and for controlling the orientation of the conveyor slider plate  424  relative to the rails  410 . Such mechanisms are known in the art. 
     Air Conditioning 
     FIG. 16 of the accompanying drawings illustrates the inspection apparatus  8  which further includes paneling around all the components heretofore described with the exclusion notably of the controller (see reference numeral  36  in FIG. 2) and the base frame  36 . The paneling, in particular, is located around the tunneling which is formed by the loading tunnel section  12 , the inspection tunnel section  14 , and the unloading tunnel section  16 , and around the x-ray line scanner subsystem  32  and the CT scanner subsystem  34 . 
     The paneling includes a plurality of contiguous panels  510  which match up with one another and which, together with the base frame  38 , define a housing  512  around the other components of the inspection apparatus  8 . 
     One of the panels  510 A is located at the first end  42  of the loading tunnel section  12 . The panel  510 A has an entry aperture  514  which is in dose proximity to the first end  42  of the loading tunnel section  12 . Another one of the panels  510 B is located at the second end  44  of the unloading tunnel section  16 . The panel  510 B has an exit aperture  515  which is in dose proximity to the second end of the unloading tunnel section  16 . 
     More of the panels  510 C and  510 D are sliding doors which are slidably mounted to the base frame  38  to provide access to the x-ray line scanner subsystem  32  and the CT scanner subsystem  34 . When the panels  510 C and  510 D are dosed, a fairly tight interface  516  is formed between the panels  510 C and  510 D. 
     From the aforegoing can generally be noted that a housing  512  is relatively airtight. 
     FIG. 17 is a view of the inspection apparatus  8  which further illustrates an air-conditioning apparatus  520  forming part of the inspection apparatus  8 . The housing  512  is shown to have an air inlet opening  522  and an air outlet opening  524 . The gantry enclosure  148  is also shown together with the ring  152  and the bearing  144  which mount the gantry enclosure  148  rotatably to the arch  40 . 
     The air-conditioning apparatus  520  includes an air inlet duct  526 , an air-conditioning unit  528 , an air supply duct  530 , a plenum  532 , a radiator  534 , and an air return duct  536 . 
     The air-conditioning unit  528  is located externally of the housing  512  and includes a fan  538 . 
     The plenum  532  is nonrotatably mounted to the support frame of the inspection apparatus (see reference numeral  10  in FIG. 2) and is in the form of a ring which is located around the ring  152 . The plenum  532  a located externally of the gantry enclosure  148  next to the first gantry plate  154  of the gantry enclosure  148 . The plenum  532  has a recessed shape which is open towards the gantry enclosure  148 . A number of air passages  542  are formed through the first gantry plate  154 . The (non-rotating) plenum  532  is located over the air passages  542  so that the confines of the plenum  532  are in communication with the confines of the (rotating) gantry enclosure  148 . 
     The radiator  534  is mounted on an outer surface of the gantry enclosure  148  and holes (not shown) are formed in the gantry enclosure  148  which place the confines of the gantry enclosure  148  in communication with the radiator  534 . Note that no fan is mounted within the gantry enclosure  148 . 
     The air inlet duct  526  has one end at atmospheric pressure and another end connected to, and in communication with, the air-conditioning unit  528 . The air supply duct  530  extends through the air inlet opening  522  and has one end connected to, and in communication with, the air-conditioning unit  528  and an opposing end connected to, and in communication with, the confines of the plenum  532 . The air return duct  536  has one end connected to, and in communication with, the air outlet opening  524  and an opposing end connected to, and in communication with, the air-conditioning unit  528 . 
     In use, air flows into the air-conditioning unit  528  when the fan  538  rotates. The air enters the air-conditioning unit  528  substantially at atmospheric pressure and atmospheric temperature. The air then passes through the air-conditioning unit  528 . The air-conditioning unit  528  lowers the temperature of the air to substantially below atmospheric temperature. The fan  538  also increases the pressure of the air to above atmospheric pressure. 
     The air is then drawn into the housing  512  through the air supply duct at above atmospheric pressure and below atmospheric temperature. The air then flows through the air supply duct  530  into the plenum  532  from where the air flows through the air passages  542  into the gantry enclosure  148 . A window  543  is located between the gantry apertures  166  and  168  so that a confined volume is defined by the window  546 , the gantry plates  154  and  156 , and the spacer  160 . A number of plates (not shown) are located at selected angles around a revolution of the gantry enclosure  148  and extend radially outward so that individual confined volume pockets are defined around a revolution of the gantry enclosure. The air enters selected ones of these pockets through selected ones of the air passages  542 , notably a pocket at the radiator  534  and a pocket in which the detectors ( 190  in FIG. 6) are located. 
     Air then flows from each pocket through holes (not shown) out of the gantry enclosure  148 . The air flows from one pocket through some of the holes in the spacer  160  to the radiator  534 . The air then passes through the radiator  534 . The radiator  534  is used for cooling the x-ray tube (see reference numeral  150  in FIG. 6) and, when operated, is at a temperature substantially above atmospheric temperature. The air is used to cool the radiator  534 . When the air flows through the radiator  534 , the temperature of the air increases somewhat, but still remains below atmospheric temperature. The air also remains above atmospheric pressure. 
     Referring now to FIG.  16  and FIG. 17 in combination, once the air passes through the radiator  534 , the air is located within a volume  540  which is externally of the tunneling provided by the loading, inspection and unloading tunnel sections  12 ,  14  and  16 , respectively, externally of the x-ray line scanner subsystem  32 , and externally of the gantry enclosure  148 , but still contained within the housing  512 . As mentioned, the housing  512  is in close proximity to and therefore seals relatively tightly on the loading and unloading tunnel sections  12  and  16 , at least to an extent sufficient to maintain the above atmospheric pressure of the air within the housing  512 . As also mentioned, the interface  516  is also relatively airtight. The housing  512 , in all other respects, is formed to maintain the above atmospheric pressure within the housing  512 . 
     The air then flows from the housing  512  through the air outlet opening  524  and the air return duct  536  back to the air-conditioning unit  528 . The air-conditioning unit  528  may control the ratios of air flowing respectively from the air inlet duct  526  and the air return duct  536  so that the air within the volume  540  remains above atmospheric pressure. 
     Because the air within the volume  540  remains above atmospheric pressure, and therefore above the pressure of the air externally of the housing  512 , the air may leak slightly from between adjacent panels  510  of the housing  512  in a direction from within the housing  512  to an area around the housing  512 . Because of the direction of leaking of air, ingress of dirt, moisture, and other contaminants into the housing  512  may be avoided. The positive pressure within the housing  512  thus protects the components within the housing  512  from dirt, moisture, and other contaminants. 
     It should be evident from the aforegoing description that the temperature of the air in the volume  540  is still below atmospheric temperature, as required for improved, more stable, and more reliable operation of components such as detector arrays which are used within the inspection apparatus  8 . 
     What should also be noted from FIG. 17 is the positioning of the fan  538 . The fan  538  is located externally of the gantry enclosure  148 . The fan  538  is thus protected from gyroscopic forces which may otherwise act on the fan  538  should the fan  538  be located on the gantry enclosure  148 . By so locating the fan  538 , the gantry enclosure  148  can be rotated at higher speeds that would otherwise be possible. The gantry enclosure  148  can also be made larger without being limited by possible malfunctioning of the fan  538 . 
     As previously mentioned, the invention is described by way of example only. In the aforegoing description and example is given of apparatus and a method for inspecting dosed containers before being loaded into a loading bay of an airplane. Such use may, for example, be for the detection of explosives within closed containers. It should however be understood that the invention is not to be limited to the inspection of a closed containers before being loaded into a loading bay of an airplane. Various aspects of the invention may for example find application in the detection of contraband and illicit materials generally, applications beyond those linked to aviation, such as rail travel, the inspection of mail or parcels, materials testing and characterization, and the inspection of patients, in particular those applications utilizing CT technology.