THE ITALIAN CONTRIBUTION TO EXCITATION FUNCTION MEASUREMENTS FOR TC-99m PRODUCTION BY PROTON BEAMS IRRADIATION

The radionuclide Tc-99m is the most commonly used radiotracer in nuclear medicine, for diagnostic purpose, due its suitable physics characteristics: T1/2 = 6.0 h, gamma emission at 140.5 keV suited for imaging via single photon emission computed tomography (SPECT) and causes minimal radiation dose to the patient. Since nowadays it is obtained by the Mo-99/Tc-99m generator, with the parent Mo-99 produced by nuclear reactor. The progressively closing process of the nuclear reactors around the world imposes to study alternative routes of Tc-99m production. Among them the direct production by the Mo-100(p,2n)Tc-99m reaction on highly enriched Mo-100 targets appears to be the most promising, even if this kind of production would solve only local or regional demand. In this prospective, due to some evident discrepancies among the excitation functions present in literature, some Laboratories start systematic experimental measurements of the cross sections and a careful analysis of the problems related to the direct production of Tc-99m by this route. In this contest we have contributed with new measurements and data set to the database of the cross sections, data that now appear more consistent and accurate. The thin-target yields have been plotted as a function of their average energy into the targets and fitted with the best mathematical function. Its integration gives the calculated thick-target yields, which allow finding the optimized couple of energy irradiation and energy loss inside the thick target to maximize the production. Some considerations about the long lived Tc-99g and the interfering radionuclides have been done.