| 摘要 |
<p>An X-ray generator has a Pierce type electron gun comprising an electron emissive cathode, field shaping electrodes connected thereto, a first accelerating anode spaced from the cathode and an X-ray target anode spaced from the accelerating anode for being impinged upon by a focused electron beam. Control grid means are disposed between the cathode and the first anode. The grid means are constructed such that with use of proper grid potentials, the electron beam may be selectively biased to cutoff or electrons can be withdrawn from selected areas of the cathode or from the entire cathode to produce focal spots of different sizes and various electron current magnitudes on the target anode.</p> |
