Determination of the activity and nuclear decay data of 157Tb.

Terbium-157 was radiochemically extracted from an irradiated tantalum target. Since the resulting material contained a significant impurity of 158Tb, 157Tb was isotopically purified using laser resonance ionization at the RISIKO mass separator in Mainz and then implanted on an aluminum (Al) foil. The implanted 157Tb was measured by two different calibrated gamma-ray spectrometers to determine photon emission rates. After dissolving the Al foil, a high purity 157Tb solution was obtained. The corresponding activity concentration was determined with a low relative uncertainty of 0.52% through a combination of liquid scintillation counting using the TDCR method and 4π(X,e)(LS)-(X,γ)(CeBr3) coincidence counting. By combining the results from all measurement techniques, emission intensities for K X-rays and gamma-rays were derived and found to be 16.05(31)% and 0.0064(2)%, respectively. The probability for K electron capture of the first forbidden non-unique transition to the ground state was determined to be 17.16(35)%. The probabilities for the electron-capture branch to the excited level and the ground state were found to be 0.084(4)% and 99.916(4)%, respectively. A Q+ value of 60.23(18) keV was estimated based on simplified BetaShape calculations, assuming an allowed transition.

Activity standardization of 99mTc by digitizer-based 4πce(LS)-γ and 4πce(PC)-γ coincidence counting.

An aqueous solution of 99mTc was standardized by means of 4πce(LS)-γ and 4πce(PC)-γ coincidence counting. The activity concentration was obtained by efficiency extrapolation relying on four different variation techniques. In both setups, fast digitizers were used for data acquisition. Detected events were recorded in list mode format, and their coincidence relationship was analyzed in the subsequent offline analysis. The combined result was used to participate in an international comparison using the Transfer Instrument of the International Reference System.

Measuring the half-life of 215Po by low-level liquid scintillation counting.

The half-life of short-lived 215Po was studied in a new experimental setup by means of liquid scintillation counting. The new value of 1.781 (5) ms was obtained by offline data analysis using the delayed coincidence method. Along with the half-life determination, a careful assessment of uncertainties was carried out. The result was compared with data available from the literature.

Half-life determination of short-lived nuclear levels in 237Np (59.54 keV), 233Pa (86.47 keV) and 227Ac (27.37 keV).

New half-life values for isomeric states in 237Np, 233Pa and 227Ac were measured by means of 4πα(LS)-γ coincidence counting with digital data acquisition. A careful assessment of uncertainties was carried out, and the new results are found to be much more precise than any previous measurement result. The half-lives were found to be T1/2Np237,E=59.54keV=67.86±0.09ns, T1/2Pa233,E=86.47keV=36.44±0.10ns and T1/2Ac227,E=27.37keV=38.56±0.15ns, respectively. A comprehensive study of literature data was undertaken for a new data evaluation that includes the results from this work.

Half-life determination of 213Bi and 209Pb by means of Cherenkov counting and detection with a NaI detector.

An 225Ac source was prepared and combined with a dedicated setup to collect recoil atoms which are ejected as a consequence of alpha decay. Some targets were made of acrylic glass and were then placed in custom-built triple-to-double coincidence ratio (TDCR) counters to measure the Cherenkov counting rates as a function of time. Half-lives of 213Bi and 209Pb were derived from the data. In addition, polyethylene films were used as targets to collect recoil atoms. These films were then measured in a well-type NaI detector to detect gamma rays. The analysis of the data yielded an independent result for the half-life of 213Bi. Combining the results of both measurement techniques, T1/2(213Bi) = (45.60 ± 0.09) min was obtained as a final value for the half-life of 213Bi. The half-life of 209Pb was found to be T1/2(209Pb) = (195.1 ± 2.6) min.

Determination of the activity of 225Ac and of the half-lives of 213Po and 225Ac.

The activity concentration of an 225Ac solution was determined by means of liquid scintillation counting using three custom-built TDCR counters. The efficiency calculation was carried out in the same way as it had been done in an earlier article on 229Th. The computation of the counting efficiency is rather complex and requires a correction to allow for the short-lived 213Po. The experimental deadtime was varied to validate the correction. One of the TDCR counters is equipped with a CAEN N6751C digitizer for data acquisition. In addition, the system comprises a CeBr3 solid scintillator as a gamma detector. The offline analysis was used to obtain a time-difference spectrum, using signals from the 213Po γ-rays at about 440 keV in the gamma channel in coincidence with the preceding beta decay as the start signal, and signals from the subsequent (delayed) 213Po alpha decays as the stop signal. After fitting an exponential function with a constant background, the half-life of 213Po was determined to be 3.709(12) µs, which is in good agreement with the evaluated value. The half-life of 225Ac was determined from long-term measurements using an ionization chamber (IC) and a TDCR system. The combined result was found to be 9.9179(30) d, which is in agreement with the outcome from Pommé et al. (2012).

Standardisation of 85Sr with digital anticoincidence counting and half-life determination of the 514 keV level of 85Rb.

The activity of a 85Sr solution was determined by means of fully digital 4πß(LS)-γ anticoincidence counting. The measurements were carried out in a custom-built, combined TDCR / 4πß(LS)-γ coincidence system, utilising a commercially available CAEN N6751C digitizer. The analysis of the experimental data, collected in list-mode format, was performed off-line by using the SoftKAM computer code developed at PTB. The data were also used to determine the half-life of the 514 keV level of 85Rb which was found to be (1020.2 ± 6.0) ns.

One- versus two-electron oxidation with peroxomonosulfate ion: reactions with iron(II), vanadium(IV), halide ions, and photoreaction with cerium(III).

The kinetics of the redox reactions of the peroxomonosulfate ion (HSO(5)(-)) with iron(II), vanadium(IV), cerium(III), chloride, bromide, and iodide ions were studied. Cerium(III) is only oxidized upon illumination by UV light and cerium(IV) is produced in a photoreaction with a quantum yield of 0.33 +/- 0.03. Iron(II) and vanadium(IV) are most probably oxidized through one-electron transfer producing sulfate ion radicals as intermediates. The halide ions are oxidized in a formally two-electron process, which most likely includes oxygen-atom transfer. Comparison with literature data suggests that the activation entropies might be used as indicators distinguishing between heterolytic and homolytic cleavage of the peroxo bond in the redox reactions of HSO(5)(-).