PURPOSE: To facilitate the control of an irradiation quantity and to enable sterilization and freeding improvement of plants without contamination of materials to be treated or ambient environment by forming low-energy X-rays from the high-energy electron beams obtd. by generating plasma in a zone segmented by a Miller magnetic field generating section and irradiating a work with these X-rays via an X-ray permeable partition wall.

CONSTITUTION: Electromagnets 3, 4, 5 are disposed at equal intervals at the proper points on the circumference of double cylindrical bodies constituting of an outside cylinder 1 formed of a nonmagnetic metallic material and an inside cylinder 2 formed of an X-ray permeable material. The outside cylinder 1 is provided with a microwave supplying port 6, a gas introducing port 7 for forming plasma and a vacuum suction port 8. Magnetic lines a, a', b, b' of magnetic force are generated by the electromagnets 3, 4, 5 and the gas for forming plasma is supplied from the gas introducing cylinder 7 into the outside cylinder 1 and is maintained under about 10-4 to 10-6 Torr. Electron cyclotron resonance plasma is formed within the outside cylinder 1 when microwaves are supplied from the microwave supplying port 6. An irradiation treatment chamber 9 is then irradiated with the low-energy X-rays generated therefrom through the inside cylinder wall.