Patent Number: 
Section: claims

1. A shielded X-ray radiation apparatus for analysis of materials via gamma activation analysis, the apparatus comprising:an X-ray conversion target, wherein, when an electron accelerator directs an electron beam having an electron beam direction at the X-ray conversion target, the X-ray conversion target generates X-rays;an X-ray attenuation shield including an elongate cavity to house the X-ray conversion target and incorporating a region to accommodate a sample;a neutron attenuation shield;a gamma attenuation shield; anda support casing housed within the X-ray attenuation shield and configured to support the X-ray conversion target and the sample,wherein the neutron attenuation shield is adjacent to and substantially surrounds the X-ray attenuation shield; andwherein the gamma attenuation shield is adjacent to and substantially surrounds the neutron attenuation shield. 2. The shielded X-ray radiation apparatus according to claim 1, wherein the X-ray conversion target is configured to generate the X-rays when the electron beam has an energy between 7 MeV and 15 MeV. 3. The shielded X-ray radiation apparatus according to claim 1, wherein the thickness of the X-ray attenuation shield at an angle of 90° from the electron beam direction measured relative to the location of the conversion target is within the range of 60-80% of the thickness in the forward direction, and the thickness at an angle of 180° from the electron beam direction measured relative to the location of the conversion target is within the range of 25-50% of the thickness in the forward direction. 4. The shielded X-ray radiation apparatus according to claim 3, wherein the thickness of the X-ray attenuation shield at an angle of 90° from the electron beam direction measured relative to the location of the conversion target is approximately 75% of the thickness in the forward direction, and the thickness at an angle of 180° from the electron beam direction measured relative to the location of the conversion target is approximately 50% of the thickness in the forward direction. 5. The shielded X-ray radiation apparatus according to claim 1, wherein a first thickness (tXR) of the X-ray attenuation shield thickness in the forward direction is estimated by the equation: tXR=TVL×log10[(R×60×106)/(r d2)], where d is the distance from the X-ray conversion target, R is the X-ray dose rate at 1 m from the X-ray conversion target produced by the X-ray conversion target, r is the shielded X-ray dose rate at the closest personnel-accessible point, and TVL is a predefined tenth value layer thickness for the X-ray attenuation shield material. 6. The shielded X-ray radiation apparatus according to claim 1, wherein the neutron attenuation shield has a thickness (tnt) in the forward direction which is estimated by the equation: tnt=TVLn log10 (f) where TVLn is a predefined tenth-value layer thickness for the attenuation of low energy neutrons in the neutron attenuation shield and f is a ratio of an unshielded neutron dose rate to a desired shielded neutron dose rate. 7. The shielded X-ray radiation apparatus according to claim 1, wherein the thickness of the neutron attenuation shield at an angle of 180° from the electron beam direction measured relative to the location of the conversion target in a rearward direction is 50% to 100% of the thickness (tnt) in the forward direction. 8. The shielded X-ray radiation apparatus according to claim 1, wherein the gamma attenuation shield has a thickness which is proportional to the thickness of the neutron attenuation shield. 9. The shielded X-ray radiation apparatus according to claim 1, wherein the X-ray attenuation shield is constructed from lead, tungsten, or layers of lead and tungsten. 10. The shielded X-ray radiation apparatus according to claim 1, wherein the neutron attenuation shield is constructed from a polymer material having a hydrogen density of approximately 0.1 g/cm3. 11. The shielded X-ray radiation apparatus according to claim 10, wherein the polymer material comprises boron or lithium. 12. The shielded X-ray radiation apparatus according to claim 1, wherein the gamma attenuation shield is constructed from lead, steel, or a composite of lead and steel. 13. The shielded X-ray radiation apparatus according to claim 1, wherein:the X-ray attenuation shield has a thickness in the electron beam direction calculated using a tabulated tenth value layer thickness for X-rays, the X-ray dose-rate output of the X-ray conversion target, and a desired X-ray dose rate outside of the shield, wherein the thickness of the X-ray attenuation shield decreases with increasing angle from the electron beam direction measured relative to the location of the conversion target; andthe neutron attenuation shield has a thickness in the electron beam direction calculated using a tabulated tenth value layer thickness for neutrons, the neutron dose-rate output of the X-ray conversion target, and a desired neutron dose rate outside of the shield, wherein the thickness of the neutron attenuation shield decreases with increasing distance from the X-ray conversion target. 14. The shielded X-ray radiation apparatus according to claim 1, further comprising the electron accelerator, wherein the electron accelerator is housed within the X-ray attenuation shield, the neutron attenuation shield, and the gamma attenuation shield. 15. The shielded X-ray radiation apparatus according to claim 14, wherein each of the X-ray attenuation shield, the neutron attenuation shield, and the gamma attenuation shield comprises:a relatively wide head portion housing the X-ray conversion target and the sample; anda relatively narrow tail portion housing at least part of the electron accelerator. 16. The shielded X-ray radiation apparatus according to claim 1, further comprising the electron accelerator, wherein at least a forward portion of the electron accelerator is housed within the support casing, the X-ray attenuation shield, the neutron attenuation shield, and the gamma attenuation shield. 17. The shielded X-ray radiation apparatus according to claim 1, wherein the support casing supports the sample and the X-ray conversion target in correct relative positions. 18. A shielded X-ray radiation apparatus for analysis of materials via gamma activation analysis, the apparatus comprising:an X-ray conversion target, wherein, when an electron accelerator directs an electron beam having an electron beam direction at the X-ray conversion target, the X-ray conversion target generates X-rays;an X-ray attenuation shield including an elongate cavity to house the X-ray conversion target and incorporating a region to accommodate a sample;a neutron attenuation shield;a gamma attenuation shield; anda removable plug configured to insert the sample into the elongate cavity;wherein the removable plug comprises adjacent blocks of material, each block having a thickness and a composition which substantially matches thickness and composition of a corresponding one of the X-ray attenuation, neutron attenuation, and gamma-ray attenuation shields;wherein the neutron attenuation shield is adjacent to and substantially surrounds the X-ray attenuation shield; andwherein the gamma attenuation shield is adjacent to and substantially surrounds the neutron attenuation shield. 19. The shielded X-ray radiation apparatus according to claim 18, wherein the removable plug further comprises a stage member on which the sample to be irradiated is locatable; and wherein the adjacent blocks of materials comprise a first block adjacent the stage member, a second block abutting the first block, and a third block abutting the second block; wherein:the first block comprises a material to substantially attenuate X-rays and having a thickness which is the same or substantially the same as the X-ray attenuation shield,the second block comprises a material to substantially attenuate neutrons and having a thickness which is the same or substantially the same as the neutron attenuation shield, andthe third block comprises a material to substantially attenuate gamma-rays with a thickness which is the same or substantially the same as the gamma attenuation shield; andwherein the shielded X-ray radiation apparatus comprises a sleeve through which the stage member is able to traverse. 20. The shielded X-ray radiation apparatus according to claim 19, wherein the sleeve of the apparatus and the removable plug have a clearance tolerance of less than 2.00 mm. 21. The shielded X-ray radiation apparatus according to claim 19, wherein the stage member of the removable plug is constructed from a substance that is free from elements that undergo significant activation from X-rays or neutrons. 22. The shielded X-ray radiation apparatus according to claim 19, wherein an outer profile of the removable plug is stepped, with at least one of the adjacent blocks increasing in width, in a direction perpendicular to a direction of travel of the removable plug with increasing distance from the stage member. 23. The shielded X-ray radiation apparatus according to claim 22, wherein the width of the or each step is in the range of 5 to 15 mm. 24. The shielded X-ray radiation apparatus according to claim 22, wherein the first block comprises at least two steps, such that the width of the first blocks increase in a stepwise fashion from the innermost to outermost steps.