An X-ray source (100, 302, 400, 403, 600) comprising: a linear accelerator having an output, said linear accelerator including a chain of electromagnetically coupled resonant cavities (52, 54) having aligned central beam apertures; an electron gun arranged to provide electrons into the linear accelerator and through the central beam apertures; means which allow microwave power to enter the resonant cavities (52, 54) to accelerate the electrons through the linear accelerator and out through said linear accelerator output, the electrons being accelerated to high energies; a first longitudinal axis (L1, L3) defined between the electron source and the linear accelerator output along which the electrons travel; a tube (106, 612) having a proximal end coupled to the linear accelerator output, said tube defining a passage having a second longitudinal axis extending through the passage, such that accelerated electrons from the linear accelerator output can enter the tube passage; a target material (108, 400, 403, 604) located within the tube (106, 612) such that accelerated high energy electrons travelling along the tube impact the target material, causing generation of X-ray radiation and emission of X-ray radiation in all directions from the target material; and shielding material (110, 314) provided around at least the portion of the tube around the target to absorb X-ray radiation emitted from the target material, wherein the second longitudinal axis is aligned with the first longitudinal axis and the shielding material (110, 314) defines a plurality of slots (112, 304, 306, 402, 404) extending from the target to an exterior surface of the shielding material, the plurality of slots to allow passage of generated radiation to form respective radiation beams, each of the slots being centered about an axis that is at an angle transverse to the first longitudinal axis (L1, L3) and the second longitudinal axis. a linear accelerator having an output, said linear accelerator including a chain of electromagnetically coupled resonant cavities (52, 54) having aligned central beam apertures; an electron gun arranged to provide electrons into the linear accelerator and through the central beam apertures; means which allow microwave power to enter the resonant cavities (52, 54) to accelerate the electrons through the linear accelerator and out through said linear accelerator output, the electrons being accelerated to high energies; a first longitudinal axis (L1, L3) defined between the electron source and the linear accelerator output along which the electrons travel; a tube (106, 612) having a proximal end coupled to the linear accelerator output, said tube defining a passage having a second longitudinal axis extending through the passage, such that accelerated electrons from the linear accelerator output can enter the tube passage; a target material (108, 400, 403, 604) located within the tube (106, 612) such that accelerated high energy electrons travelling along the tube impact the target material, causing generation of X-ray radiation and emission of X-ray radiation in all directions from the target material; and shielding material (110, 314) provided around at least the portion of the tube around the target to absorb X-ray radiation emitted from the target material, wherein the second longitudinal axis is aligned with the first longitudinal axis and the shielding material (110, 314) defines a plurality of slots (112, 304, 306, 402, 404) extending from the target to an exterior surface of the shielding material, the plurality of slots to allow passage of generated radiation to form respective radiation beams, each of the slots being centered about an axis that is at an angle transverse to the first longitudinal axis (L1, L3) and the second longitudinal axis.