Determination of noble elements in coins by gamma activation analysis

Silver and gold were analysed in coins and medals by inelastic gamma-scattering reaction. The irradiation was performed with a 740 TBq (20 kCi)⁶⁰Co source. After irradiation the isomer activities were measured with a well type NaI(Tl) scintillation counter and evaluated by means of a software program.     

Measurement of103mRh produced by the103Rh/γ, γ′ /103mRh reaction with liquid scintillation counting

A liquid scintillation counting technique was applied to measure the isotope^103mRh /half life = 56.12 min/ which is difficult to detect because its -ray is of low energy and low emission probability. Tris-/2,4-pentanedionato/ rhodium /III/ /Rh/ acac/₃/ was irradiated with bremsstrahlung of accelerated 3.2 MeV electrons by LINAC. The method has given a reliable calibration curve for the determination of^103mRh radioactivity below Rh/acac/₃ concentrations of 2 mM. The integrated cross section of¹⁰³Rh/,/^103mRh determined by this method was found to be 6.8±3.4 b MeV at 3.2 MeV.     

Integral cross section of the99Tc(γ,γ′)99mTc reaction at 4 MeV

^99mTc production was studied with the aid of photoexcitation by a 4 MeV endpoint energy bremsstrahlung from the LINAC of the Institute of Isotopes, Budapest. The intensity of the -flux was monitored by disc-shaped natural indium plates, placed in front of and behind the small cylindrical aluminium holders containing TcO₂ samples in a powder form. Isomeric activities were measured through the 140 keV -line by a Ge spectrometer. The integral cross section at 4 MeV was found to be 63.3±7.1 bMeV, which can be considered reasonable compared to the corresponding value of 55.3 bMeV established for the¹¹⁵In (,)^115mIn reaction. We also attempted the photoexcitation of^99mTc by irradiation with -rays from a 1.5×10¹⁵ Bq⁶⁰Co source, but no isomeric activity could be observed. This places the first activation level between 1.33 and 4 MeV.