CATHODE STRUCTURE OF ROTARY ANODE X-RAY TUBE

PURPOSE:To obtain a rotary anode X-ray tube with a cathode structure capable of concurrently being used for expansion stereo photographing and for contact stereo photographing by providing two pairs of cathodes having two faces forming a ridge at the top and having a focusing unit carved with a groove storing a filament different in size on each face. CONSTITUTION:Faces forming a ridge inclined at an angle theta in relation to an electrode center line are provided on the top of focusing electrodes 3a, 3b respectively, and filaments 4a, 4b, 5a, 5b are stored in focusing grooves carved on these faces so that the distance between a large focal point (a) and a small focal point (b) and the distance between a large focal point (a') and a small focal point (b') generated on a target are made predetermined length L3 respectively. These focusing electrodes 3a, 3b are fitted on a holder 6 at a predetermined distance (l) apart from a plane passing through the tube center respectively so that the small focal points (b), (b') are aligned at a focal distance L1 and the large focal points (a), (a') are aligned at a focal distance L2 on the target 2, thus two pairs, large and small, of focal point groups with different focal point sizes and focal distance respectively can be formed.