TC-95 AND TC-96 PRODUCTION BY (GAMMA,XN) REACTIONS

The Tc-99(gamma,3n) Tc-96 and Tc-99(gamma,4n) Tc-95 reactions were stu died by irradiation of target Tc-99 with bremsstrahlung from the linea r electron accelerator of Tohoku University, up to 50 MeV gamma-energy . The resulting Tc-96 (4.3 d) and Tc-95 (20 h) activities were determi ned by gamma-spectrometry. The gamma-flux was monitored by the Tc-99(g amma,gamma')Tc-99m reaction. Metallic copper and gold foils were used as additional flux monitors in front of and behind the samples. Their measured radioactivity was utilized for normalizing bremsstrahlung flu x calculations, in order to determine reaction cross sections. Cross s ections were also determined theoretically, performing calculations in the framework of a neutron cascade evaporation model. Above the (gamm a,3n) and (gamma,4n) threshold energies the neutron emission channel w as supposed to be the only open channel for deexcitation following pho toabsorption. The preequilibrium contribution was considered negligibl e. The experimental results obtained for the integrated cross section at 30 and 50 MeV fit reasonably well the calculated curves.