Patent Number: 
Section: claims

1. A method for changing a pathlength of positively charged particles through a liquid, comprising the steps of:transporting the positively charged particles from an accelerator, along a beam line, and into an exit nozzle system;providing a first chamber of said exit nozzle system, said first chamber comprising:an incident side comprising an incident aperture;an exit side comprising an exit aperture; anda beam path of the positively charged particles from the incident aperture to the exit aperture;filling the beam path in said chamber with the liquid;changing a length of the beam path between the incident aperture and the exit aperture by moving said first chamber radially across a longitudinal axis of the positively charged particles. 2. The method of claim 1, further comprising the step of:pumping a second volume of the liquid into said first chamber to dissipate radioactivity in said first chamber. 3. The method of claim 1, further comprising the step of:replacing the liquid in the beam path between the incident aperture and the exit aperture with a gas; andafter said step of replacing, said exit nozzle system targeting a tumor with a second batch of the positively charged particles. 4. The method of claim 3, further comprising the step of:alternating said steps of: (1) filling the beam path with the liquid and (2) replacing the liquid in the beam path between the incident aperture and the exit aperture with a gas. 5. The method of claim 1, further comprising the step of:placing a water tight seal over the incident aperture, said water tight seal within one inch of a first ionization strip detector positionally responsive to passage of the positively charged particles; anddetecting first electrons emitted from said first ionization strip detector to determine a first axis position of the positively charged particles. 6. The method of claim 5, further comprising the step of:positioning a second ionization strip detector within one inch of said first ionization strip detector;detecting second electrons emitted from said second ionization strip detector to determine a second axis position of the positively charged particles.