Patent Number: 
Section: claims

1. A method for producing a radionuclide, comprising the steps of:completely filling a target chamber with target fluid including a target material, the target chamber including an upper region and a lower region below the upper region;pressurizing the target chamber by flowing a gas toward a lower opening of the lower region;applying a particle beam to the target chamber at a beam power to irradiate the target material and produce a radionuclide in the target fluid; andwhile applying the particle beam, maintaining a space including a target fluid vapor in the upper region by preventing target fluid from flowing out from the target chamber from the upper region while permitting target fluid heated by the particle beam to flow through the lower opening against the gas pressure, and permitting a volume of the target fluid vapor space to vary in proportion to the beam power of the particle beam being applied to the target chamber. 2. The method of claim 1 further comprising, during application of the particle beam, condensing target fluid vapor in the upper region and flowing the condensed target fluid to the lower region. 3. The method of claim 1 further including, during application of the particle beam, cooling the target fluid that flowed out from the target chamber. 4. The method of claim 1 wherein the heated target fluid flowing out from the target chamber through the lower opening is flowed into a second chamber fluidly communicating with the lower opening. 5. The method of claim 4 wherein pressurizing includes flowing the gas into the second chamber. 6. A method for producing a radionuclide, comprising the steps of:completely filling a target chamber with target fluid including a target material, the target chamber including an upper region and a lower region below the upper region;pressurizing the target chamber;applying a particle beam to the target chamber to irradiate the target material and produce a radionuclide in the target fluid; andwhile applying the particle beam, preventing target fluid from flowing out from the target chamber from the upper region, maintaining a space including a target fluid vapor in the upper region, and maintaining an open target fluid flow path from a lower opening of the lower region to a second chamber to enable target fluid heated by the particle beam to flow out from the target chamber toward the second chamber during application of the particle beam. 7. The method of claim 6 wherein pressurizing the target chamber includes flowing a gas into the second chamber, and wherein the heated target fluid is flowed out from the target chamber through the lower opening against the gas pressure. 8. The method of claim 6 wherein the second chamber includes an expansion chamber. 9. The method of claim 6 wherein the second chamber includes an expansion chamber fluidly communicating with the lower opening via a lower liquid conduit. 10. The method of claim 6 wherein the second chamber includes a lower liquid conduit. 11. The method of claim 6 further comprising providing a target fluid return path from the second chamber to the lower opening during application of the particle beam. 12. The method of claim 6 further comprising, during application of the particle beam, condensing target fluid vapor in the upper region and flowing the condensed target fluid to the lower region. 13. The method of claim 6 wherein the particle beam is applied to the target chamber at a beam power, the target fluid vapor space has a volume, and the method includes permitting the volume of the target fluid vapor space to vary in proportion to the beam power of the particle beam being applied to the target chamber.