Patent Number: 048184683
Section: summary

BACKGROUND OF THE INVENTION 1. Field of the Invention .sup.123 I has many advantages as a radionuclide for medicinal purposes. The radiation dose resulting from .sup.123 I is much reduced as compared to .sup.131 I or .sup.125 I. For most scanning situations .sup.123 I allows scanning to be accomplished with an acceptable dose. In addition, the gamma radiation emitted is ideal for imaging with scintillation cameras. The relatively short half-life of .sup.123 I allows other radionuclides to be used as well in diagnostic procedures without interference. The radiations resulting from .sup.123 I are readily shielded, so as to decrease radiation hazard to personnel. While the half-life is relatively short, the .sup.123 I half-life is sufficiently long to allow for purification and chemical labeling of compounds, delivery to the clinician, and utilization of the .sup.123 I by the clinician. Finally, .sup.123 I does not have undesirable particulate radiation. In preparing the .sup.123 I there are a number of significant considerations. Important to the process is the production of .sup.123 I without the concomitant formation of other radionuclides which cannot be conveniently separated from the desired radionuclide and have undesirable properties, for example, particulate radiation. Because the equipment employed for the preparation of radionuclides is expensive and large amounts of energy are utilized, it is desirable that the use of the energy employed be highly efficient as it relates to the yield of the desired radionuclide. Other considerations include the cost of the target material, ease of processing, speed of processing and the like. DESCRIPTION OF THE PRIOR ART U.S. Pat. No. 3,694,313 discloses a process for preparing .sup.123 I from .sup.122 Te powder with alpha particles while passing a low flow rate helium stream through the powder to remove the xenon which is formed. U.S. Pat. No. 3,226,298 teaches irradiating tellurium dioxide with thermal neutrons at a temperature of at least about 550.degree. C. and then separating radioactive iodine-131 by distillation. Fusco, et al, J. of Nuclear Medicine 13, 729 (1972) describes the preparation of .sup.123 I by proton irradiation of .sup.127 I in a batch process. Weinreich, et al, Int. J. of Applied Radiation and Isotopes, 25, 535 (1974) teaches the preparation of .sup.123 I by irradiating solid sodium iodide in the presence of a continuous helium stream. SUMMARY OF THE INVENTION A method is provided for preparing medicinally and isotopically pure .sup.123 I by irradiating an XI (X is alkali metal or iodine) target with high energy particles to produce .sup.123 Xe. The target material is maintained in the liquid state, providing reflux as required, with a continual stream of helium, optionally containing xenon, passing through the target area, while maintaining the target temperature in a predetermined range. The helium carrier aids in temperature control and sweeps out the .sup.123 Xe radionuclide which is trapped in a cold trap and then purified by pumping the radioactive .sup.123 Xe to the final decay vessel.