Patent Number: 
Section: claims

1. A positron beam apparatus comprising:an electron source;a positron beam source;a sample stage for mounting a sample;electron beam irradiation system for focusing an electron beam emitted from said electron source and irradiating the focused electron beam onto said sample;an electron beam position controlling system for controlling irradiating position of electron beam on said sample;positron beam irradiation system for irradiating positron beam on said sample;a detector for detecting electromagnetic waves generated from said sample by irradiation of said electron beam and positron beam;a controller for synchronizing information of irradiating position of said electron beam and output signals of said detector to generate an image signal;means for displaying said image signal,wherein said positron beam sources comprises a plurality of positron sources;a shield with a window, through which positron beams pass, placed between said sample stage and said plurality of positron sources; andmeans for moving one positron source out of said plurality of positron sources to a position where emitted positrons pass through said window part,wherein said plurality of positron sources have different nuclides from each other. 2. A positron beam apparatus according to claim 1, further comprising means for scanning said positron beam across said sample. 3. A positron beam apparatus according to claim 1, comprising means for cooling said sample. 4. A positron beam apparatus according to claim 1, wherein at least two γ-ray detectors are used as said detector and at the least two said γ-ray detectors are placed opposite each other across said sample stage. 5. A positron beam apparatus according to claim 1, wherein said detector is a γ-ray detector. 6. A positron beam apparatus according to claim 5, further comprising means for shielding the γ-ray detector which is placed between said γ-ray detector and positron source. 7. A positron beam apparatus according to claim 1, further comprising means for focusing said positron beam. 8. A positron beam apparatus according to claim 1, further comprising an electron beam decelerator between said sample stage and said electron beam irradiation system. 9. A positron beam apparatus according to claim 8, wherein said electron beam decelerator includes a solenoid type magnetic field generating device. 10. A positron beam apparatus according to claim 1, comprising:a secondary electron detector to detect secondary electrons generated from a sample by electron beam irradiation,wherein said image display means displaying not only said imaging signal but also secondary electron images. 11. A positron beam apparatus according to claim 1, wherein a path of a positron beam and a path of an electron beam are placed opposite each other across said sample stage.