Patent Number: 
Section: claims

1. A charged particle radiation device having a charged particle source, an extraction electrode for extracting charged particles from the charged particle source, a sample holding means for holding a sample to be irradiated with charged particles extracted by the extraction electrode, a charged particle optical system for irradiating the sample held on the sample holding means with the charged particles that are extracted, a first evacuation means for evacuating a first vacuum chamber in which the charged particle source is arranged, and a second vacuum chamber, independent of the first vacuum chamber, for evacuating a second vacuum chamber connected to the first vacuum chamber, the charged particle radiation device further having:a shielding electrode of a cylindrical structure that is so arranged as to surround the charged particle source and shield against the procession of back scattered charged particles from the extraction electrode, wherein:the top end and the bottom end of the cylinder of the cylindrically structured shielding electrode are open to the inside of the first vacuum chamber. 2. The charged particle radiation device according to claim 1, wherein:the shielding electrode is arranged farther away than the shortest distance between the tip of the charged particle source and the extraction electrode. 3. The charged particle radiation device according to claim 1, wherein:the extraction electrode has a protrusion smaller than the shortest distance between the tip of the charged particle source and the extraction electrode. 4. The charged particle radiation device according to claim 1, wherein:the extraction electrode is a convex extraction electrode. 5. The charged particle radiation device according to claim 1, wherein:the height of the tip of the charged particle source is arranged within the range in the height direction of the first evacuation means. 6. The charged particle radiation device according to claim 1, wherein:the first evacuation means is an entrapment type pump. 7. The charged particle radiation device according to claim 6, wherein:the entrapment type pump is a non-evaporative getter pump or a titanium sublimation pump. 8. A charged particle radiation device having a charged particle source, an extraction electrode for extracting charged particles from the charged particle source, a sample holding means for holding a sample to be irradiated with charged particles extracted by the extraction electrode, a charged particle optical system for irradiating the sample held in the sample holding means with the charged particles that are extracted, a first evacuation means for evacuating a first vacuum chamber in which the charged particle source is arranged, and a second vacuum chamber, independent of the first vacuum chamber, for evacuating a second vacuum chamber connected to the first vacuum chamber, the charged particle radiation device further having:a shielding electrode of a cylindrical structure that is so arranged as to surround the charged particle source and shield against the procession of back scattered charged particles from the extraction electrode, wherein:at least one opening is provided in the side face of the cylinder of the cylindrically structured shielding electrode. 9. The charged particle radiation device according to claim 8, wherein:the shielding electrode is arranged farther away than the shortest distance between the tip of the charged particle source and the extraction electrode. 10. The charged particle radiation device according to claim 8, wherein:the plurality of openings provided in the side of the cylinder are provided with protrusions directed outside the cylinder. 11. The charged particle radiation device according to claim 8, wherein:the shielding electrodes are arranged in a plurality in a telescopic way, andthe opening provided in each shielding electrode is arranged in a position out of alignment with others not to superpose correspondingly to the loci of the back scattered charged particles. 12. The charged particle radiation device according to claim 8, wherein:the side of the shielding electrode has an inclination relative to the center axis thereof. 13. The charged particle radiation device according to claim 8, wherein:the shielding electrode has a mesh structure. 14. The charged particle radiation device according to claim 8, wherein:power sources capable of independently applying voltages to the shielding electrode, the charged particle source and the extraction electrode are installed. 15. The charged particle radiation device according to claim 8, wherein:the power source to apply a voltage to the shielding electrode is common to the power source to apply a voltage to the charged particle source. 16. The charged particle radiation device according to claim 8, wherein:the power source to apply a voltage to the shielding electrode is common to the power source to apply a voltage to the extraction electrode. 17. The charged particle radiation device according to claim 8, further having:an electrode that restrains the back scattered charged particles toward above the shielding electrode. 18. The charged particle radiation device according to claim 8, further having:a directional energy source that gives heat or electric fields to the tip of the charged particle source. 19. The charged particle radiation device according to claim 18, wherein:the directional energy source is a semiconductor laser. 20. The charged particle radiation device according to claim 8, further having:a means to heat the shielding electrode.