Patent Number: 047138335
Section: claims

1. An X-ray source apparatus comprising, in an evacuated chamber, an X-ray target of a selected material which emits X-rays when bombarded with electrons of at least a predetermined energy; a source of electrons; means for accelerating electrons from said source to at least the predetermined energy; means for generating a magnetic field with curved lines of magnetic flux interlinking said target and said electron source and with the magnetic field having sufficient strength over the whole of the interlinking magnetic flux lines between said target and said electron source such that electrons of the energies of those accelerated from said source with components at angles to the magnetic field are constrained by the field to execute helical paths adjacent said source and to travel generally in the direction of the lines of flux, said target being sized and positioned to intercept substantially all of those lines of flux that intercept said electron source so that substantially all the electrons from said source bombard said target to cause said target to emit X-rays; and aperture means blocking straight line paths between said source and said target but permitting passage of substantially all the electrons travelling along the flux lines from said source to said target. 2. Apparatus as claimed in claim 1 wherein said target is at earth potential and the means for accelerating comprises an earthed grid or iris along the lines of flux interlinking said source and said target and means for producing an electron accelerating electrical potential gradient between the source and the grid or iris. 3. Apparatus as claimed in claim 1 further comprising means defining a specimen region; and wherein said target is located adjacent the specimen region in the magnetic field to irradiate a specimen in the specimen region. 4. Apparatus as claimed in claim 3 wherein said specimen region defining means includes means for evacuating said specimen region to a pressure different from the pressure in the evacuated chamber. 5. Apparatus as claimed in claim 1 wherein said means for accelerating comprises an earthed grid or iris along the lines of flux interlinking said source and said target and means for producing an electron accelerating electrical potential gradient between said source and said grid or iris. 6. Apparatus as claimed in claim 1 wherein said electron source comprises a wire filament arranged to extend in a line at an acute angle to the lines of flux at said source, and a DC voltage source to heat said filament. 7. Apparatus as claimed in claim 1 wherein said electron source comprises a wire filament arranged to extend in a circle in a plane perpendicular to the lines of flux at said source, and a DC voltage source connected to heat said filament with a DC current directed about said filament to cause a force on said filament directed radially outwards thereof. 8. Apparatus as claimed in claim 1 wherein said magnetic field generating means generates a magnetic field in the order of about 7 Tesla.