INTEGRAL CROSS-SECTION OF THE TC-99 (GAMMA,GAMMA') TC-99M REACTION AT4 MEV

Tc-99m production was studied with the aid of photoexcitation by a 4 M eV endpoint energy bremsstrahlung from the LINAC of the Institute of I sotopes, Budapest. The intensity of the gamma-flux was monitored by di sc-shaped natural indium plates, placed in front of and behind the sma ll cylindrical aluminium holders containing TcO2 samples in a powder f orm. Isomeric activities were measured through the 140 keV gamma-line by a Ge spectrometer. The integral cross section at 4 MeV was found to be 63.3 +/- 7.1 mubMeV, which can be considered reasonable compared t o the corresponding value of 55.3 mubMeV established for the In-115(ga mma, gamma')In-115m reaction. We also attempted the photoexcitation of Tc-99m by irradiation with gamma-rays from a 1.5 x 10(15) Bq Co-60 so urce, but no isomeric activity could be observed. This places the firs t activation level between 1.33 and 4 MeV.