Production of long-lived isomers by 4 MeV endpoint energy bremsstrahlung

Long-lived isomers of ⁸⁷ Sr, ¹⁰³Rh, ¹¹¹Cd, ^{113, 115}In, ¹¹⁷Sn, ¹⁷⁶Lu, ¹⁸⁹Os, ¹⁹³Ir and ¹⁹⁵Pt were produced by means of bremsstrahlung from a 4 MeV end-point energy 25 A intensity electron beam. Isomeric ativities were measured by gamma-spectrometry. Photoex-citation exhibits a steep rise as compared to lower energy excitations of prior experiments by high activity ¹³⁷Cs, ⁶⁰Co, ¹⁴²Pr and ²⁴Na sources. The large variety in the magnitude of the excitation cross section may mostly arise from largely di?ering isomer ratios governed by spin differences between isomeric and ground levels, and likely by di?erences in the multipole character of the upward transitions, too. Isomer excitation seems to exhibit loose correlations with the product of photoabsorption cross section and isomer ratio derived from (n, n′) reactions on the one hand, and with the product of valence proton and neutron numbers and isomer ratio on the other hand.     

Production of long-lived isomers by 4 MeV endpoint energy bremsstrahlung

Long-lived isomers of⁸⁷Sr,¹⁰³Rh,¹¹¹Cd,^113,115In,¹¹⁷Sn,¹⁷⁶Lu,¹⁸⁹Os,¹⁹³Ir and¹⁹⁵Pt were produced by means of bremsstrahlung from a 4 MeV endpoint energy 25µA intensity electron beam. Isomeric activities were measured by gamma-spectrometry. Photoexcitation exhibits a steep rise as compared to lower energy excitations of prior experiments by high activity¹³⁷Cs,⁶⁰Co,¹⁴²Pr and²⁴Na sources. The large variety in the magnitude of the excitation cross section may mostly arise from largely differing isomer ratios governed by spin differences between isomeric and ground levels, and likely by differences in the multipole character of the upward transitions, too. Isomer excitation seems to exhibit loose correlations with the product of photoabsorption cross section and isomer ratio derived from (n,n′) reactions on the one hand, and with the product of valence proton and neutron numbers and isomer ratio on the other hand.     

Angular and dose dependence of CR-39 neutron response for shape-selected tracks

A shape selection method corresponding to an energy discrimination was used to eliminate unwanted events disturbing evaluation of CR-39 detectors in detecting tracks induced by particles both of perpendicular and oblique incidence. The angular dependence of the response was examined, detecting fast neutrons from ²⁵²Cf with shape selection technique at various angles and distances. Also, the CR-39 track detectors with the ²⁵²Cf source were exposed to high γ-intensity of a ⁶⁰Co irradiation facility in the range 0.1 to 4.5 kGy, similar to the exposures inside spent fuel assemblies. Using the two functions the lower limit of burnup could be determined by the method.     

Monitoring neutrons from spent reactor fuel by bubble detectors

In order to eliminate the strong temperature-dependence of bubble detectors used for spent fuel assay, a simple way could be to keep them in the water pond but far from fuel assemblies before exposure for about 20 min, until the detectors warm up. Fast neutrons from fuel assemblies in the Paks Nuclear Power Plant, Hungary, were detected by BD-100R type detectors at 28°C (in winter) and at 35°C in summer). Calibration was performed by a standard ²⁵²Cf source in borated water. Burnup monitoring inside fuel assemblies can be provided by smaller diameter detectors prepared from BD-100R type ones.     

A new detection method of99Tc by nuclear excitation

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 product^99mTc which emits -ray measurable with ease by a semiconductor detector. The production rate of^99mTc 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.     

Gamma spectrometry in the ITWG CMX-4 exercise

Journal of Radioanalytical and Nuclear Chemistry - Low enriched uranium samples of unknown origin were analyzed by 16 laboratories in the context of a Collaborative Materials Exercise (CMX),...     

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.     

95Tc and96Tc production by (γ, xn) reactions

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.     

Uranium assay of fuel rods by passive gamma-ray spectrometry

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.