Electrostatic ion accelerator

Abstract

A high current (0.2 to at least 2 milliamperes), low-energy (2.2 to 4 MV) ion beam is generated and is utilized to produce clinically significant quantities of medical isotopes useful in applications such as positron emission tomography. For a preferred embodiment, a tandem accelerator is utilized. Negative ions generated by a high current negative-ion source are accelerated by an electrostatic accelerator in which the necessary high voltage is produced by a solid state power supply. The accelerated ions then enter a stripping cell which removes electrons from the ions, converting them into positive ions. The positive ions are then accelerated to a target which is preferably at ground potential. For a preferred embodiment, the solid state power supply utilized to develop the required voltages is a cascade rectifier power supply which is coaxial with the accelerator between the ion source and the stripper, and is designed to have a voltage gradient which substantially matches the maximum voltage gradient of the accelerator.

What is claimed is: .[. 
     
       1.  An electrostatic ion accelerator comprising: a negative ion source adapted for generating a minimum ion current of approximately 0.2 milliamperes,   a high voltage terminal,   a stripping cell located in said terminal,   a first accelreating column connected between said ion source and said stripping cell,   a second accelerating column connected between said stripping cell and said target,   means connected to said first and second accelerating columns for maintaining a high vacuum therein, and   solid state power supply means connected to said ion source and said terminal for supplying a positive potential of at least 1MV to said terminal..]. .[.   
     
     
       2.  An accelerator according to claim 1 wherein said solid state power supply means is coaxial with said first accelerating column and has a voltage gradient which substantially matches the maximum voltage gradient of said accelerating column..]. .[.3. An accelerator according to claim 2 wherein said solid state power supply means is a cascade rectifier power supply..]. .[.4. An accelerator according to claim 1 wherein said solid state power supply means is a cascade rectifier power supply..]. .[.5. An accelerator according to claim 1 wherein said solid state power supply supplies a positive potential of approximately 1.1 to 2MV..]. .[.6. An accelerator according to claim 1 wherein said stripping cell is a field-free gas-filled cell..]. .[.7. An accelerator according to claim 1 
     
     
        wherein said stripping cell is a water vapor jet stripper..]. 8. Apparatus for producing .[.medically active.]. .Iadd.clinically significant quantities of .Iaddend.radioisotopes by bombarding targets maintained at substantially ground potential with accelerated ions, said apparatus comprising a negative ion source adapted for generating a .[.minimum.]. .Iadd.predetermined .Iaddend.ion current .[.of approximately 0.2 milliamperes.].,   a high voltage terminal,   a stripping cell located in said terminal,   a first accelerating column connected between said ion source and said stripping cell,   a second accelerating column connected between said stripping cell and said target,   means connected to said first and said second accelerator columns for maintaining a high-vacuum therein, and   means connected to said ion source and said terminal for supplying a positive potential of less than 2 MV to said terminal.Iadd.;   said predetermined current being high enough so that a clinically significant isotope yield is produced at the final beam energy for the   
     
     
        beam.Iaddend.. 9. Apparatus as claimed in claim 8 wherein said radioisotope is oxygen-15, and 
     
     
       wherein said target is a nitrogen-containing substance. 10. Apparatus as claimed in claim 8 wherein said radioisotope is carbon-11 , and 
     
     
       wherein said target is a boron-containing substance. 11. Apparatus as claimed in claim 8 wherein said radioisotope is nitrogen-13 , and 
     
     
       wherein said target is a carbon-containing substance. 12. Apparatus as claimed in claim 8 wherein said radioisotope is fluorine-18 , and 
     
     
       wherein said target is a neon-containing substance. 13. Apparatus as claimed in claim 8 wherein said means for supplying a positive potential includes a cascade rectifier power supply electrically connected to said ion source and said terminal, said power supply comprising a plurality of 
     
     
        voltage multiplier stages. 14. Apparatus as claimed in claim 13 wherein said cascade rectifier power supply is coaxial with said first accelerating column, and wherein the voltage gradient of said power supply is substantially equal to   
     
     
        the maximum voltage gradient of the first accelerating column. 15. Apparatus as claimed in claim 8 wherein said stripping cell is a 
     
     
        field-free gas-filled cell. 16. Apparatus as claimed in claim 8 wherein 
     
     
        said stripping cell is a water vapor jet stripper. 17. Apparatus as claimed in claim 8 wherein said means for supplying a positive potential 
     
     
        supplies a potential of approximately 1.1 to 2MV. 18. Apparatus as claimed 
     
     
        in claim 8 wherein said target is a solid target. 19. A method for producing .[.medically active.]. .Iadd.clinically significant quantities .Iaddend.of radioisotopes by bombarding a target of a suitable substance and maintained at a reference potential with accelerated ions, said method comprising the steps of: generating an ion beam of .Iadd.predetermined current .Iaddend.from an ion source, .[.said ion beam having a minimum ion current of approximately 0.2 milliamperes;.]. and   accelerating the ion beam from the ion source to the target, the final beam energy at the target being in the range of approximately 2.2 up to 4 MV.Iadd.;   said predetermined current being high enough so that a clinically significant isotope yield is produced at the final beam energy for the   
     
     
        beam.Iaddend.. 20. A method as claimed in claim 19 wherein said accelerating step includes the steps of accelerating said ion beam through a first accelerating column, the voltage drop across the first accelerating column being in the range of approximately 1.1 to 2 MV, reversing the polarity of said ion beam, and accelerating the ion beam with its polarity reversed through a second accelerating column to the target, the voltage drop across the second column being substantially the 
     
     
        same as the voltage drop across the first column. 21. A method as claimed in claim 20 wherein said ion beam source is a negative ion beam source; wherein said polarity reversing step includes the step of stripping electrons from the accelerated negative ions in a stripping cell to generate a positive ion beam output; and   
     
     
       wherein the positive ion beam is accelerated to the target. 22. A method as claimed in claim 19 wherein said radioisotope is oxygen-15; and 
     
     
       wherein said target is a nitrogen containing substance. 23. A method as claimed in claim 19 wherein said radioisotope is carbon-11; and 
     
     
       wherein said target is a boron containing substance. 24. A method as claimed in claim 19 wherein said radioisotope is nitrogen-13; and 
     
     
       wherein said target is a carbon containing substance. 25. A method as claimed in claim 19 wherein said radioisotope is fluorine 18; and 
     
     
       wherein said target is a neon containing substance. 26. A method for producing .[.medically active.]. .Iadd.clinically significant quantities of .Iaddend.radioisotopes by bombarding a target maintained at substantially ground potential with accelerated ions, said method comprising the steps of: generating a negative ion beam having a .[.minimum.]. .Iadd.predetermined .Iaddend.ion current .[.of approximately 0.2 milliamperes.].;   accelerating said ion beam through a first accelerating column, the voltage drop across the first accelerating column being less than 2MV;   stripping electrons from the accelerated negative ions in a stripping cell to generate a positive ion beam output; and   accelerating the positive ion beam through a second accelerating column to the target, the voltage drop across the second column being substantially the same as the voltage drop across the first column .[.and the beam current at the target being a minimum of approximately 0.2 milliamperes.]..Iadd.;   said predetermined current being high enough so that a clinically significant isotope yield is produced at the final energy for the   
     
     
        beam.Iaddend.. 27. Apparatus for producing epithermal neutrons for medical treatment of tumors comprising an ion source for generating an ion current of at least one milliampere,   a high voltage terminal,   a stripping cell located within the high-voltage terminal,   a lithium target,   a first accelerating column connected between said ion source and said stripping cell,   a second accelerating column connected between said stripping cell and said target,   means connected to said first and said second accelerator columns for maintaining a high-vacuum therein, and   a solid state power supply electrically connected to said ion source and said high-voltage terminal for supplying a positive high-voltage potential of at least 1 MV to said terminal.