Nuclear isomers of half-lives above one second have been excited from the ground state of stable nuclides via inelastic γ-ray
scattering by using bremsstrahlung of a 4 MeV, 22 μA linear electron accelerator. This method is potentially useful for a
number of elements in elemental analysis by virtue of its high specificity and, in some cases good sensitivity. As there is
no need for special sample preparation, this kind of activation may be preferable in some applications. Detection sensitivities
have been determined for 15 elements, and possibilities in routine chemical analysis are discussed.
The spontaneous gamma-rays characteristic of uranium isotopes can be detected and measured in order to identify the isotopic
composition of uranium and to assay its total amount in various objects and materials. In order to test these methods of passive
gammaray spectrometry in practice, the235U-enrichment of a known fuel rod was determined by counting 186 keV gammas from235U with Ge(Li) detectors of different volumes. The 1001 keV gammas characteristic to238U were counted too. Expected counting rates of 186 keV and 1001 keV gammas for WWER fuels are given and the suitability of
passive gamma-ray spectrometry for the determination of235U-enrichment and for the assay of total uranium in reactor fuels are discussed based on these measurements.
Authors:T. Sekine, K. Yoshihara, J. Sáfár, L. Lakosi, and Á. Veres
The99Tc (, 3n)96Tc and99Tc (, 4n)95Tc reactions were studied by irradiation of target99Tc with bremsstrahlung from the linear electron accelerator of Tohoku University, up to 50 MeV -energy. The resulting96Tc (4.3 d) and95Tc (20 h) activities were determined by -spectrometry. The -flux was monitored by the99Tc (,
)99mTc 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 flux calculations, in order to determine reaction cross sections. Cross sections were also determined theoretically, performing calculations in the framework of a neutron cascade evaporation model. Above the (, 3n) and (, 4n) threshold energies the neutron emission channel was supposed to be the only open channel for deexcitation following photoabsorption. The preeguilibrium contribution was considered negligible. The experimental results obtained for the integrated cross section at 30 and 50 MeV fit reasonably well the calculated curves.
Authors:T. Sekine, K. Yoshihara, Zs. Németh, L. Lakosi, and Á. Veres
A new nuclear excitation process,99Tc (,
)99mTc reaction, was applied for the first time to radioactivation analysis of technetium. Bremsstrahlung irradiation of99Tc samples gave the reaction product99mTc which emits -ray measurable with ease by a semiconductor detector. The production rate of99mTc per g99Tc was linearly correlated with the flux of bremsstrahlung. The detection limit of99Tc was estimated to be nanogram order (0.63 Bq99Tc) under the optimum irradiation condition. Possible interference by100Ru(, p)99mTc reaction was also studied, which could be discriminated from the (,
) reaction by simultaneously occurring98Ru (, p)97Ru reaction.
Authors:T. Sekine, K. Yoshihara, I. Pavlicsek, L. Lakosi, and Á. Veres
A liquid scintillation counting technique was applied to measure the isotope103mRh /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 of103mRh 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.
Authors:J. Sáfár, L. Lakosi, I. Pavlicsek, A. Veres, T. Sekine, and K. Yoshihara
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 of99mTc 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.