A NEW HIGH YIELD CRYOGENIC TARGET FOR FLUORINE-18 PRODUCTION

THIS PROJECT'S OBJECTIVE IS TO DEVELOP A HIGH YIELD, HIGH RELIABILITY CRYOGENIC ICE TARGET FOR THE PRODUCTION OF THE MOST WIDELY USED POSITRON EMISSION TOMOGRAPHY (PET) RADIOISOTOPE, (18)F(FLUORINE-18). CURRENT CYCLOTRON-BASED PET SYSTEMS USE SMALL VOLUME (18)O(OXYGEN-18) ENRICHED LIQUID WATER TARGETS TO PRODUCE (18)F VIA THE (18)O(P,N)(18)F NUCLEAR REACTION. HOWEVER, THESE TARGETS SUFFER FROM SOME BEAM CURRENT LIMITATIONS CAUSED BY TARGET THINNING THAT RESULTS FROM BUBBLES FORMED IN THE WATER FROM LOCAL BOILING AND RADIOLYSIS. THESE EFFECTS ALSO DECREASE THE RELIABILITY OF WATER TARGETS; THE YIELD OBTAINED CAN VARY FROM BATCH TO BATCH BY AS MUCH AS A FACTOR OF TWO. THEPLANNED ICE TARGET ADDRESSES BOTH OF THESE CONCERNS BY SIGNIFICANTLY REDUCING THE RADIOLYSIS RATE AND ELIMINATING BOILING. IN ADDITION, THE LOW VAPOR PRESSURE OF ICE AT TEMPERATURES BELOW -100 DEGREES CENTIGRADE PERMITS THE TARGET TO BE WINDOWLESS. THIS CHARACTERISTIC ELIMINATES THEMAINTENANCE AND RELIABILITY PROBLEMS ASSOCIATED WITH THIN-METAL FOIL ACCELERATOR WINDOWS. PRELIMINARY CALCULATIONS INDICATE THAT THIS TARGET WILL ALLOW EXISTING PET CYCLOTRONS TO PRODUCE SUBSTANTIALLY HIGHER (18)F YIELDS THAN ARE CURRENTLY AVAILABLE. THE PHASE I RESEARCH WILL ANSWER QUESTIONS ON SPECIFICS OF TARGET MATERIAL AND SUBSTRATE COOLING, RADIOLYSIS IN CRYOGENIC ICE, AND DENSITY OF THE DEPOSITED ICE LAYER.