FORMATION OF 99mTc BY THE (γ,γ') NUCLEAR EXCITATIONDepartment of Chemistry, Faculty of Science, Tohoku University Sendai 980, Japan Zsolt Németh, László Lakosi, Árpád Veres Institute of Isotopes, H-1525 Budapest, P.O. Box 77, Hungary A new activation process to obtain 99mTc has been studied by (γ,γ') excitation of its ground state isomer 99Tc(2.1×105y). Bremsstrahlung irradiation of the target 99Tc using an electron linear accelerator gave radioactivities of 99mTc(6.0hr), 96Tc(4.3d) and 95Tc(20hr). The integrated cross section of 99Tc for the 99Tc(γ,γ')99mTc process was found to be (0.9~2.0)×10-26MeV⋅cm2 for incident electron energy 15~50MeV. Based on the above results, the (γ,γ') reaction was applied to radioactivation analysis of 99Tc for the first time. The production rate of 99mTc and the detection limit of 99Tc were 0.048Bq 99mTc/Bq99Tc and 3ng99Tc(50pCi) at 50MeV incident electron energy for 3hr irradiation, respectively. KEYWORDS: 99Tc(γ,γ')99mTc, integrated cross section, radioactivation analysis of 99Tc |