We study the production of radioisotopes for nuclear medicine in (gamma,gamma) photoexcitation reactions or (gamma,xn + yp) photonuclear reactions for the examples of ^195mPt, ^117mSn and ^44Ti with high flux [(10^13 - 10^15) gamma/s], small beam diameter and small energy band width (Delta E/E ~ 10^-3 -10^-4) gamma beams. In order to realize an optimum gamma-focal spot, a refractive gamma-lens consisting of a stack of many concave micro-lenses will be used. It allows for the production of a high specific activity and the use of enriched isotopes. For photonuclear reactions with a narrow gamma beam, the energy deposition in the target can be reduced by using a stack of thin target wires, hence avoiding direct stopping of the Compton electrons and e^+e^- pairs. The well-defined initial excitation energy of the compound nucleus leads to a small number of reaction channels and enables new combinations of target isotope and final radioisotope. The narrow-bandwidth gamma excitation may make use of collective resonances in gamma-width, leading to increased cross sections. (gamma,gamma) isomer production via specially selected gamma cascades allows to produce high specific activity in multiple excitations, where no back-pumping of the isomer to the ground state occurs. The produced isotopes will open the way for completely new clinical applications of radioisotopes. For example ^195mPt could be used to verify the patients response to chemotherapy with platinum compounds before a complete treatment is performed. In targeted radionuclide therapy the short-range Auger and conversion electrons of ^195mPt and ^117mSn enable a very local treatment. The generator ^44Ti allows for a PET with an additional gamma-quantum (gamma-PET), resulting in a reduced dose or better spatial resolution.
Download