초록 ▼

An X-ray source is disclosed comprising a source of high energy electrons that travel along a longitudinal path. Target material lies along the longitudinal path and X-ray radiation is generated due to impact of the high energy electrons with the target. Shielding material is provided around at leas

An X-ray source is disclosed comprising a source of high energy electrons that travel along a longitudinal path. Target material lies along the longitudinal path and X-ray radiation is generated due to impact of the high energy electrons with the target. Shielding material is provided around at least a portion of the target. The shielding material defines a slot extending from the target to an exterior surface of the shielding material, to allow passage of generated radiation. The slot has an axis transverse to the longitudinal path. The axis may be perpendicular longitudinal path. The shielding material may define a plurality of slots having transverse axes. The source of high energy electrons may be a linear accelerator, for example. Scanning systems incorporating such sources are also disclosed. The scanning system comprises a conveying system having a longitudinal axis and the radiation source may be positioned so that the longitudinal path forms an acute angle with respect to the longitudinal axis, to decrease the size of the scanning unit as compared to a unit where the longitudinal axis is perpendicular to the longitudinal path. The longitudinal axis may be parallel to the longitudinal path, to form a more compact scanning system. A plurality of slots may be defined in the shielding material and a corresponding number of conveying systems may be provided to examine a plurality of objects concurrently. Methods of generating radiation and methods of examining objects are also disclosed.

대표청구항 ▼

I claim: 1. An X-ray source comprising: a housing defining a chamber to accelerate electrons and an output of the chamber, the chamber having a first longitudinal axis, wherein the output is aligned with the first longitudinal axis to allow passage of accelerated electrons from the chamber; a tube

I claim: 1. An X-ray source comprising: a housing defining a chamber to accelerate electrons and an output of the chamber, the chamber having a first longitudinal axis, wherein the output is aligned with the first longitudinal axis to allow passage of accelerated electrons from the chamber; a tube defining a passage having a second longitudinal axis, the tube having a proximal end coupled to the output of the housing such that the second longitudinal axis is aligned with the first longitudinal axis and accelerated electrons can enter the passage; a target material within the tube, wherein impact of the target material by accelerated electrons causes generation of X-ray radiation; and non-rotatable shielding material around at least a portion of the tube around the target, the shielding material defining a slot therethrough to allow passage of generated radiation during operation; wherein the slot is centered about an axis transverse to the first and second longitudinal axes. 2. The X-ray source of claim 1, further comprising a source of electrons to emit electrons into the chamber, along the first longitudinal axis, the source being supported by the housing. 3. The X-ray source of claim 2, wherein; the housing defines an input opening to the chamber; and the source of electrons is coupled to the input opening. 4. The X-ray source of claim 1, wherein the target is at the distal end of the tube. 5. The X-ray source of claim 1, wherein the shielding material surrounds the entire tube and a portion of the housing proximate the tube. 6. The X-ray source of claim 1, wherein the axis of the slot forms an angle with the first and second axes of from 80 to 90 degrees. 7. The X-ray source of claim 1, wherein the slot defines a fan beam or a cone beam. 8. The X-ray source of claim 1, wherein the shielding material defines a plurality of slots extending from the target to the exterior surface of the shielding material, the slots being transverse to the first and second axes. 9. The X-ray source of claim 8, wherein at least some of the slots have a respective axis perpendicular to the first and second axes. 10. The X-ray source of claim 8, further comprising a respective shutter coupled to the housing adjacent to at least some of the slots to selectively open and close those slots. 11. The X-ray source of claim 1, further comprising: a bend magnet; a second tube coupling the bend magnet to the output of the housing, wherein the proximal end of the first tube is coupled to the output of the housing by the bend magnet and the second tube; a third tube having a first end coupled to the bend magnet; a second target material within the third tube; and shielding material around at least a portion of the third tube surrounding the target material; whereby electrons exiting the housing are selectively directed through the first or third tube, to the first or second target, respectively, by the bend magnet. 12. The X-ray source of claim 11, wherein the bend magnet is an electromagnet. 13. The X-ray source of claim 11, further comprising: a second bend magnet; and a fourth tube coupling the first bend magnet to the second bend magnet; wherein: the third tube is coupled to the first bend magnet through the fourth tube and the second bend magnet; and the second tube, the bend magnet and the first target are aligned along the first and second longitudinal axes. 14. The X-ray source of claim 1, wherein the target is a refractory metal. 15. The X-ray source of claim 1, wherein the target is tungsten. 16. The X-ray source of claim 1, wherein the shielding material is chosen from the group consisting of tungsten, steel and lead. 17. The X-ray source of claim 1, wherein the housing defines a linear accelerator. 18. The X-ray source of claim 17, wherein the linear accelerator accelerates electrons to a selected one of a plurality of energies. 19. The X-ray source of claim 1, wherein: the chamber is adapted to accelerate electrons such that impact of the target material by accelerated electrons causes generation of X-ray radiation having a peak energy of at least 1 MeV. 20. The X-ray source of claim 1, wherein: the slot extends from proximate the target to an exterior surface of the shielding material. 21. An X-ray source comprising: a linear accelerator defining a chamber to accelerate electrons and an output of the chamber, the chamber having a first longitudinal axis, wherein the output is aligned with the first longitudinal axis to allow passage of accelerated electrons from the chamber; a source of electrons associated with the chamber to emit electrons along the first longitudinal axis; a tube defining a passage having a second longitudinal axis, the tube having a proximal end with an input coupled to the output of the housing such that the second longitudinal axis is aligned with the first longitudinal axis and accelerated electrons can enter the passage; a target material of refractory metal at the distal end of the tube, along the second longitudinal axis, wherein impact of the target material by electrons causes generation of X-ray radiation; and shielding material around at least a portion of the tube around the target, the shielding material defining a slot, therethrough to allow passage of generated radiation resulting from impact of the emitted electrons on the target, during operation; wherein the slot being centered about an axis forming an angle with the first and second longitudinal axes within a range of 90 degrees plus or minus 10 degrees; and the slot extending only partially around the second longitudinal axis. 22. The X-ray source of claim 21, wherein the shielding material defines a plurality of slots extending from the target to the exterior surface of the shielding material, each of the plurality of slots forming respective angles with the first and second axes within a range of 90 degrees plus or minus 10 degrees. 23. The X-ray source of claim 21, wherein; the slot extends up to 110 degrees around the second longitudinal axis. 24. The X-ray source of claim 21, wherein: the slot extends from proximate the target to an exterior surface of the shielding material. 25. An X-ray source, comprising: a source of high energy electrons, wherein the high energy electrons travel along a longitudinal path; a target material lying along the longitudinal path of the high energy electrons, the target material generating X-ray radiation due to impact of the high energy electrons with the target; and non-rotatable shielding material around at least a portion of the target, the shielding material defining a slot therethrough to allow passage of radiation resulting from impact of the high energy electrons on the target, during operation; wherein: the slot is centered about an axis transverse to the longitudinal path; and the slot extends only partially around the longitudinal path. 26. The X-ray source of claim 25, wherein the axis of the slot forms an angle with the longitudinal path within a range of 90 degrees plus or minus 10 degrees. 27. The X-ray source of claim 25, wherein the shielding material defines a plurality of slots extending from the target to an exterior surface of the shielding material. 28. The X-ray source of claim 27, wherein the axis of each of the plurality of slots forms respective angles with the longitudinal path of within a range of 90 degrees plus or minus 10 degrees. 29. The X-ray source of claim 25, wherein the source of high energy electrons comprises: a source of electrons; and an accelerating chamber to receive electrons from the source and to accelerate the electrons. 30. The X-ray source of claim 29, wherein the accelerating chamber is a linear accelerator. 31. The X-ray source of claim 25, wherein the shielding material is around a portion of the path to the target. 32. The X-ray source of claim 31, wherein the path extends, at least in part, through the source of high energy electrons. 33. The X-ray source of claim 32, wherein the shielding material is around at least a portion of the source of high energy electrons. 34. The X-ray source of claim 25, wherein the path is defined in part by a tube extending from the source of high energy electrons, wherein the shielding material is around at least a portion of the tube. 35. The X-ray source of claim 25, wherein; the slot extends up to 110 degrees around the second longitudinal axis. 36. The X-ray source of claim 35, wherein; the slot extends up to 90 degrees around the second longitudinal axis. 37. A system for examining an object, comprising: a conveyor system to move the object through the system along a longitudinal axis; and a source of radiation comprising: a source of high energy electrons, wherein the high energy electrons travel along a longitudinal path; a target material lying along the longitudinal path of the high energy electrons, the target material generating radiation due to impact of the high energy electrons with the target; and non-rotatable shielding material around at least a portion of the target, the shielding material defining a slot therethrough to allow passage of generated radiation, during operation; wherein: the slot is centered about an axis transverse to the longitudinal path; and the radiation source is positioned with respect to the conveying system such that radiation emitted through the slot will irradiate an object for inspection on the conveying system. 38. The scanning system of claim 37, wherein the radiation source is on a first side of the conveying system, the system further comprising: a detector on a second side of the conveying system, to detect radiation transmitted through the object. 39. The scanning system of claim 37, wherein the source of radiation is a source of X-ray radiation. 40. The scanning system of claim 37, wherein the radiation source has a longitudinal axis and the longitudinal path and the longitudinal axis form an acute angle. 41. The scanning system of claim 40, wherein the acute angle is less than or equal to 45 degrees. 42. The scanning system of claim 41, wherein the acute angle is less than or equal to 10 degrees. 43. The scanning system of claim 37, wherein the radiation source has a longitudinal axis and the longitudinal path and the longitudinal axis are parallel. 44. The scanning system of claim 37, wherein the shielding material further defines a second slot centered about a second axis transverse to the longitudinal path to emit generated radiation; the scanning system further comprising: a second conveying system to move an object through the system along a second longitudinal axis parallel to the first longitudinal axis, wherein the second slot is positioned to emit generated radiation to irradiate an object on the second conveying system. 45. The scanning system of claim 44, further comprising: first and second shutters mechanically coupled to the system proximate the first and second slots, respectively, to selectively open and close the respective slot. 46. The scanning system of claim 44, wherein the shielding material further defines a third slot centered about a third axis transverse to the longitudinal path to emit generated radiation; the scanning system further comprising: a third conveying system to move an object through the system along a third longitudinal axis parallel to the first longitudinal axis, wherein the third slot is positioned to emit generated radiation to irradiate an object on the third conveying system. 47. The scanning system of claim 46, wherein the shielding material defines a fourth slot centered about a fourth axis transverse to the longitudinal path to emit generated radiation; the scanning system further comprising: a fourth conveying system to move an object through the system along a fourth longitudinal axis parallel to the first longitudinal axis, wherein the fourth slot is positioned to emit generated radiation to irradiate an object on the fourth conveying system. 48. The scanning system of claim 37, wherein the axis of the slot forms an angle with the longitudinal path within a range of 90 degrees plus or minus 10 degrees. 49. A scanning system to examine objects, comprising: a conveyor system to move the object through the system along a longitudinal axis; a source of high energy electrons to emit electrons along a path; a bend magnet along the path; a first target material, the target material generating X-ray radiation due to impact of the high energy electrons with the target; and first shielding material around the first target material, the shielding material defining a first slot therethrough, the first slot being centered about an axis transverse to the path; a second target material, the target material generating X-ray radiation due to impact of the high energy electrons with the target; and second shielding material around the second target material, the second shielding material defining a second slot therethrough, the second slot being centered about an axis transverse to the path; wherein: the bend magnet is capable of selectively directing the high energy electrons to the first or the second target; and the first slot and the second slot are positioned with respect to the first conveying system to allow passage of generated radiation to irradiate different sides of the object on the conveying system, during operation. 50. The scanning system of claim 49, wherein the first target and the first bend magnet are aligned with the path, the system further comprising: a second bend magnet, wherein the first bend magnet is capable of selectively directing the high energy electrons to the first target or the second bend magnet, the second bend magnet capable of directing the high speed electrons to the second target. 51. An X-ray scanning system to examine an object, comprising: a conveyor system to move the object through the system along a first longitudinal axis; and an elongated X-ray source configured to emit X-ray radiation with a peak energy of at least 1 MeV, during operation, the X-ray source having a second longitudinal axis and comprising a source of charged particles and a target, wherein the source of charged particles and the target lie along the second longitudinal axis and the charged particles travel from the source of charged particles to the target, along the second longitudinal axis; wherein the X-ray source is supported adjacent to the conveying system such that the first longitudinal axis is parallel to the second longitudinal axis. 52. The X-ray scanning system of claim 51, wherein the X-ray source is on a first side of the conveying system, the system further comprising: a detector on a second side of the conveying system, to detect X-ray radiation transmitted through the object. 53. The X-ray scanning system of claim 51, wherein: the source of charged particles comprises a source of high energy electrons; and shielding material around at least a portion of the target, the shielding material defining a slot therethrough to emit generated radiation; wherein: the slot is centered about an axis transverse to the longitudinal axis; and the source is positioned with respect to the conveying system such that radiation emitted through the slot will irradiate an object for inspection on the conveying system. 54. The X-ray scanning system of claim 53, wherein the shielding material defines a plurality of slots to emit generated radiation, wherein each slot is centered about an axis transverse to the longitudinal path. 55. The X-ray scanning system of claim 53, wherein: the axis of the slot is perpendicular to the longitudinal axis. 56. The X-ray scanning system of claim 51, wherein: the X-ray source further comprises a tube defining a passage along the second longitudinal axis; and the target is within the tube. 57. A method of generating X-ray radiation, comprising: colliding high energy electrons traveling along only a single axis with a target, the target being surrounded radially with respect to the axis by non-rotating shielding material, to generate radiation; and collimating the generated radiation into a radiation beam in a direction transverse to the axis and extending only partially around the axis by a slot through the shielding material. 58. The method of claim 57, wherein the high energy electrons are formed by accelerating electrons through a chamber. 59. The method of claim 58, wherein the chamber has an outlet lying along the longitudinal path, the method comprising: colliding the accelerated electrons with a target displaced from the outlet of the chamber. 60. The method of claim 57, comprising collimating the radiation emitted from the target into a radiation beam forming an angle with the axis within a range of 90 degrees plus or minus 10 degrees. 61. The method of claim 57, comprising collimating the radiation emitted from the target into a plurality of radiation beams, each beam being transverse to the longitudinal path. 62. The method of claim 57, comprising: collimating the generated radiation by a slot transverse to the axis. 63. The method of claim 57, comprising: colliding high energy electrons, having a peak energy of at least 1 MeV, with the target. 64. A method of examining contents of an object with a radiation source, the method comprising: colliding high energy electrons traveling along a longitudinal path from a source to a point target along the path, the target being surrounded by non-rotating shielding material, to generate radiation; collimating the generated radiation into at least one radiation beam transverse to the longitudinal path by at least one respective slot through the shielding material, wherein the at least one respective slot extends only partially around the longitudinal path; irradiating the object with the radiation; and detecting radiation interacting with the object. 65. The method of claim 64, wherein the radiation source comprises a chamber having a longitudinal axis and an outlet along the longitudinal axis, the method comprising generating radiation to irradiate the object by: accelerating electrons through the chamber; and colliding the electrons with a target displaced from the outlet of the chamber. 66. The method of claim 64, comprising conveying the object along a second axis substantially parallel to the longitudinal path, through the radiation beam. 67. The method of claim 64, further comprising: emitting a plurality of radiation beams from the source, each radiation beam being emitted in a direction transverse to the longitudinal axis; irradiating a respective plurality of objects with the plurality of radiation beams; and detecting radiation interacting with each of the objects. 68. The method of claim 64, comprising irradiating the object with X-ray radiation. 69. The method of claim 64, comprising irradiating a cargo container. 70. The method of claim 64, comprising: detecting radiation transmitted through the object. 71. The method of claim 64, comprising: collimating the generated radiation by a slot transverse to the axis. 72. The method of claim 64, comprising: colliding high energy electrons traveling undeflected along the longitudinal path, from the source to the point target, with the point target. 73. An X-ray source comprising: a housing defining a chamber to accelerate electrons and an output of the chamber, the chamber having a first longitudinal axis, wherein the output is aligned with the first longitudinal axis to allow passage of accelerated electrons from the chamber; a tube defining a passage having a second longitudinal axis, the tube having a proximal end coupled to the output of the housing such that the second longitudinal axis is aligned with the first longitudinal axis and accelerated electrons can enter the passage; a target material within the tube, wherein impact of the target material by accelerated electrons causes generation of X-ray radiation; and shielding material around at least a portion of the tube around the target, the shielding material defining a slot therethrough, the slot to allow passage of generated radiation, during operation; wherein the slot is centered about an axis transverse to the first and second longitudinal axes; the source further comprising: a bend magnet; a second tube coupling the bend magnet to the output of the housing, wherein the proximal end of the first tube is coupled to the output of the housing by the bend magnet and the second tube; a third tube having a first end coupled to the bend magnet; a second target material within the third tube; and second shielding material around at least a portion of the third tube surrounding the second target material, the second shielding material defining a second slot therethrough; whereby electrons exiting the housing are selectively directed through the first or third tube, to the first or second target, respectively, by the bend magnet. 74. The X-ray source of claim 73, wherein the bend magnet is an electromagnet. 75. The X-ray source of claim 73, further comprising: a second bend magnet; and a fourth tube coupling the first bend magnet to the second bend magnet; wherein: the third tube is coupled to the first bend magnet through the fourth tube and the second bend magnet; and the second tube, the bend magnet and the first target are aligned along the first and second longitudinal axes. 76. The X-ray source of claim 75, wherein the second bend magnet is an electromagnet or a permanent magnet. 77. The X-ray source of claim 73, wherein: the first and second slots each have a first dimension and a second dimension; and the first dimension and the axis of each slot lie in respective planes transverse to the first and second longitudinal axes. 78. The X-ray source of claim 73, wherein: the chamber is adapted to accelerate electrons such that the impact of the first and second target material by the accelerated electrons causes generation of X-ray radiation having a peak energy of at least 1 MeV. 79. A radiation source comprising: a source of charged particles; a target material, wherein charged particles emitted by the source travel along a longitudinal path from the source to the target material, the target material generating radiation due to impact of the charged particles with the target, the radiation having a peak energy of at least 1 MeV, during operation, the longitudinal path lying along a longitudinal axis; and shielding material around at least a portion of the target, the shielding material defining a slot therethrough to allow passage of generated radiation, during operation; wherein the slot has a first dimension and a second dimension perpendicular to the first dimension, the first dimension lying in a plane including the longitudinal axis, the slot being centered about an axis in the first plane forming an angle with the longitudinal axis within a range of 90 degrees plus or minus 10 degrees, and the slot extends in the second dimension only partially around the longitudinal axis. 80. The radiation source of claim 79, further comprising: a housing defining a chamber to accelerate the charged particles and an output of the chamber to allow passage of accelerated charged particles from the chamber, along the longitudinal path; and a tube defining a passage, the tube having a proximal end coupled to the output of the housing such that the longitudinal path of the charged particles extends along the passage; wherein: the target material is within the tube, along the longitudinal path; and the shielding material is around at least a portion of the tube around the target. 81. The radiation source of claim 79, wherein: the shielding material is non-rotatable. 82. The radiation source of claim 81, wherein: the shielding material is immobile. 83. The radiation source of claim 79, wherein: the slot defines a fan beam with a width; and the first dimension defines the width of the fan beam. 84. The radiation source of claim 79, wherein; the slot extends up to 110 degrees around the second longitudinal axis. 85. The radiation source of claim 84, wherein; the slot extends up to 90 degrees around the second longitudinal axis. 86. A source of X-ray radiation comprising: a housing defining a chamber to accelerate electrons and an output of the chamber, the chamber having a first longitudinal axis, wherein the output is aligned with the first longitudinal axis to allow passage of accelerated electrons from the chamber; a tube defining a passage having a second longitudinal axis, the tube having a proximal end coupled to the output of the housing such that the second longitudinal axis is aligned with the first longitudinal axis and accelerated electrons can enter the passage; a target material within the tube, wherein impact of the target material by accelerated electrons causes generation of radiation having a peak energy of at least 1 MeV; and immobile shielding material around at least a portion of the tube around the target, the shielding material defining a slot therethrough; wherein the slot has a first dimension and a second dimension perpendicular to the first dimension, the first dimension being in a plane transverse to the first and second longitudinal axes, to allow passage of generated radiation, during operation. 87. The source of claim 86, wherein: the slot defines a fan beam; and the first dimension defines a width of the fan beam. 88. The radiation source of claim 86, wherein: the plane forms an angle within a range of 90 degrees plus or minus 10 degrees with the first and second longitudinal axes. 89. A radiation source comprising: a source of charged particles; a target material lying along a path traversed by the charged particles, wherein impact of the charged particles with the target causes generation of radiation; first shielding material around at least a portion of the target, the first shielding material defining a plurality of slots therethrough, at least some of the plurality of slots to allow passage of generated radiation, during operation; and multiple units of second shielding material movably coupled to the source to selectively place at least some of the plurality of respective slots in an opened state or a closed state to selectively allow passage of generated radiation through at least some of the plurality of respective slots. 90. The radiation source of claim 89, wherein: the multiple units of second shielding material are pivotally coupled to the radiation source. 91. The radiation source of claim 89, wherein: at least one of the plurality of slots has a first dimension and a second dimension perpendicular to the first dimension, the first dimension lying in a plane transverse to the path. 92. The radiation source of claim 91, wherein: the plane forms an angle with the path within a range of 90 degrees plus or minus 10 degrees. 93. The radiation source of claim 91, wherein: at least one of the plurality of slots defines a fan beam with an arc; and the first dimension defines the arc of the fan beam. 94. A system for examining an object, comprising: at least first and second conveyor systems to position objects for examination; and a source of radiation comprising: a source of charged particles; a target material, wherein the charged particles travel from the source to the target material during operation, the target material generating radiation due to impact of the charged particles with the target material; shielding material around at least a portion of the target, the shielding material defining at least first and second slots therethrough to allow passage of generated radiation; wherein: the radiation source is positioned with respect to the first and second conveyor systems such that radiation passing through the first and second slots irradiate objects on the first and second conveyor systems, respectively, for examination; and the system further comprising: means for opening and closing the first slot to selectively allow passage of generated radiation; and means for opening and closing the second slot to selectively allow passage of generated radiation. 95. The system of claim 94, wherein: the first and second conveyor systems move respective objects through the system along first and second longitudinal paths, respectively. 96. The system of claim 94, comprising: the longitudinal axes of the first and second conveyor systems are each parallel to the longitudinal path of the charged particles. 97. The system of claim 94, wherein: the first slot and at least some of the second slots have a first dimension and a second dimension perpendicular to the first dimension; and the first dimensions of the first and the at least some of the second slots lie in respective planes transverse to a longitudinal axis of the source. 98. The system of claim 97, further comprising: a fourth conveyor system to position an object for examination; wherein: the shielding material defines a fourth slot therethrough; and the radiation source is positioned with respect to the fourth conveyor system such that radiation passing through the fourth slot will irradiate an object on the fourth conveyor system for examination; and means for opening and closing the fourth slot, to selectively allow passage of generated radiation. 99. The system of claim 98, wherein: the first, second, third, and fourth slots each have a first dimension and a second dimension perpendicular to the first dimension; and each of the first dimensions lie one or more respective planes transverse to a longitudinal axis of the source. 100. The system of claim 94, further comprising: a third conveyor system to position an object for examination; wherein: the shielding material defines a third slot therethrough; and the radiation source is positioned with respect to the third conveyor system such that radiation passing through the third slot will irradiate an object on the third conveyor system for examination; and means for opening and closing the third slot, to selectively allow passage of generated radiation. 101. A method of generating radiation, comprising: colliding charged particles with a target along first axis to generate radiation having a peak energy of at least 1 MeV; and collimating the generated radiation into a radiation beam centered about a second axis forming an angle with the first axis within a range of 90 degrees plus or minus 10 degrees, the radiation beam extending only partially around the first axis. 102. A radiation scanning system to examine an object, comprising: a conveyor system to move an object through the system along a first longitudinal axis; and an elongated radiation source comprising a source of charged particles and a point target along a second longitudinal axis, wherein the charged particles travel along the second longitudinal axis from the source of charged particles to the target during operation, the radiation source emitting radiation with a peak energy of at least 1 MeV, during operation; wherein the radiation source is supported adjacent to the conveying system such that the first longitudinal axis and the second longitudinal axis are parallel or form an angle of up to 45 degrees. 103. The system of claim 102, wherein the first longitudinal axis and the second longitudinal axis are parallel or form an angle of up to 10 degrees. 104. The system of claim 102, wherein the radiation source is an X-ray radiation source. 105. A radiation source comprising: a source of charged particles; a target material lying along a path traversed by the charged particles, wherein of the charged particles with the target causes generation of radiation; first shielding material around at least a portion of the target, the first shielding material defining a plurality of slots therethrough, at least some of the plurality of slots allow passage of generated radiation, during operation; and second shielding material coupled to the source to selectively open and close at least some of the plurality of slots. 106. A method of examining contents of an object with a radiation source, the method comprising: colliding high energy electrons traveling along a longitudinal path from a source to a point target along the path, the target being surrounded by non-rotating shielding material, to generate radiation; collimating the generated radiation into at least one radiation beam transverse to the longitudinal path by at least one respective slot through the shielding material; irradiating the object with the radiation; and detecting radiation transmitted through the object.