Activity standard and calibrations for 227Th with ingrowing progeny.

Thorium-227 was separated from its progeny and standardized for activity by the triple-to-double coincidence ratio (TDCR) method of liquid scintillation counting. Confirmatory liquid scintillation-based measurements were made using efficiency tracing with 3H and live-timed anticoincidence counting (LTAC). The separation time and the efficiency of the separation were confirmed by gamma-ray spectrometry. Calibrations for reentrant pressurized ionization chambers, including commercial radionuclide calibrators, and a well-type NaI(Tl) detector are discussed.

A new evaluation of the decay data for 166Ho.

The ß--emitter 166Ho is of interest as a potential radiolabel for therapeutic medical applications. A new decay data evaluation for 166Ho has been performed using the Decay Data Evaluation Project (DDEP) methodology. New recommended values for the half-life, γ-ray emission probabilities, ß-- branching ratios, and other relevant nuclear and atomic data are provided. This paper provides a summary of the evaluation; the complete set of recommended data tables and detailed evaluator comments are available at the DDEP website.

DDEP re-evaluation of the radioactive decay scheme of 137Cs.

A complete re-evaluation of the 137Cs ß‒ decay scheme has been performed within the scope of the Decay Data Evaluation Project (DDEP), taking full advantage of the most recent measurements. An evaluated half-life of 30.018 (22) years is recommended, along with a full revision of the ß‒ decay branching ratios that also results in a re-evaluation of the absolute emission probability of the 662-keV gamma ray to give a value of 85.01 (20)%. Recommendations for new measurements are also suggested.

Liquid scintillation efficiencies, gamma-ray emission intensities, and half-life for Gd-153.

Gadolinium-153 was standardized for activity by live-timed anticoincidence counting and an ampoule was submitted to the international reference system (SIR). Absolute emission intensities for the main γ rays were determined with calibrated high-purity germanium (HPGe) and lithium-drifted silicon (Si(Li)) detectors. A revised decay scheme is indicated, with no probability of direct electron capture to the 153Eu ground state. Triple-to-double coincidence ratio (TDCR) efficiency curves indicate that the revised decay scheme is consistent with experiment. Half-life measurements agree with a previous NIST determination and show no sensitivity to chemical environment.

Development of BNBSL: A ß-ν spectra library for spectrometry applications.

While modern nuclear decay data can provide many details of a given nuclides ß-decay modes (branching ratios, decay heating etc.), knowledge of the emitted ß-energy spectrum is often not included. This limitation hampers the use of decay data in some analysis, such as ß-spectrometry of irradiated material, prediction of ß-decay Bremsstrahlung or antineutrino, ν̄, detection. To address this deficiency, and for increased ease of ß-spectrometry studies of complex samples, a library of ß, ν and Bremsstrahlung-spectra, called BNBSL (Beta-Neutrino-Bremsstrahlung spectra library), has been produced. It has been found that the content compares favourably with experimental data and methodologies for its application to complex nuclear inventories have been developed. BNBSL contains spectra for over 1500 nuclides, which is hoped will benefit applied nuclear, radiation and materials science studies.

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.

Alpha-decay half-life of Hafnium isotopes reinvestigated by a semi-empirical approach.

- New estimates of partial α-decay half-life, T1/2, for 156-162,174,176Hf isotopes by a semi-empirical, one-parameter model are given. The used model is based on the quantum mechanical tunneling mechanism through a potential barrier, where the Coulomb, centrifugal and overlapping components to the barrier have been considered within the spherical nucleus approximation. This approach enables to reproduce, within a factor 2, the measured T1/2 of ground-state to ground-state (gs-gs) α-transitions for the artificially produced 156-162Hf isotopes. Half-life predictions for α-transitions from the ground-state of 159,161Hf isotopes to the first gamma-excited level of 155,157Yb isotopes are reported for the first time. The model also provides T1/2-values of (2.43±0.28)×1016 a and (1.47±0.19)×1020 a for the naturally occurring 174Hf and 176Hf isotopes, respectively, in quite good agreement with a number of estimates by other authors. In addition, the present methodology indicates that 174,176Hf isotopes exhibit α-transition to the first gamma-excited level of their daughter Ytterbium isotopes which half-lives are found (0.9±0.1)×1018 a and (0.72±0.08)×1022 a, respectively, with a chance of being measured by improved α-detection and α-spectrometry methods available nowadays.

226Th nuclear decay data evaluation.

Following the recent evaluation of the nuclear decay data of 230U, a similar evaluation for its daughter, 226Th, a radionuclide of interest for targeted alpha therapy, was undertaken within the Decay Data Evaluation Project (DDEP) and an IAEA Coordinated Research Project. The nuclear decay data presented are: the half-life, decay energy, alpha-particle emission energies and probabilities, internal conversion coefficients and gamma-ray energies and emission intensities. These new data will be included in the DDEP database NUCLEIDE.

Towards high-precision calculation of electron capture decays.

Based on previous study, the calculation of electron capture decays has been improved by considering a more accurate atomic model with precise atomic energies, and different radiative corrections have been tested. The computer code has been revised in order to greatly speed-up the calculation and has then been coupled with the BetaShape code. The influence of the nuclear component has also been explored using a simple nuclear model. All the calculations are compared with precise measurements available in the literature.

Alpha-particle emission probabilities of 231Pa derived from first semiconductor spectrometric measurements.

The nuclide 231Pa is a member of the 235U decay chain. It is a complex alpha emitter with 25 identified alpha emissions. Formerly published alpha-particle emission probabilities were derived from measurements taken with magnetic spectrometers. This work presents the first measurements made with semiconductor detectors. High-resolution alpha-particle spectrometry was carried out at CIEMAT and JRC using ion-implanted planar silicon detectors. Alpha-particle emission probabilities of 23 transitions were derived from deconvolutions of the spectra. For the major lines, uncertainties are lower than 1%, a significant improvement to existing data. The new data set will allow a more accurate evaluation of the decay scheme of 231Pa.

Updated decay data evaluation for 68Ga.

The updated evaluation of the decay data for the radionuclide 68Ga is presented. The evaluated data have been obtained using the methodology adopted in the Decay Data Evaluation Project (DDEP). Particular attention is paid to obtaining the recommended value for the 68Ga half-life from the discrepant data set. The recent half-life measurements do not improve the data consistency of this data set. The different statistical procedures are used to select the recommended value of 67.77 (14) min for the 68Ga half-life.

Measurement of absolute γ-ray emission probabilities in the decay of 227Ac in equilibrium with its progeny.

The emission probabilities of γ rays produced in the 227Ac decay series were determined by high-resolution γ-ray spectrometry of sources with standardised activity. The sources were prepared quantitatively on glass discs by drop deposition of a solution with 227Ac in radioactive equilibrium with its daughter nuclides. Their activity was measured by a primary standardisation technique based on alpha-particle counting at a defined low solid angle. Four laboratories performed γ-ray spectrometry and derived absolute γ-ray intensities. Mean values were calculated and compared with literature data and the currently recommended evaluated data. New values on certain γ-ray emission probabilities are proposed.

Standardization of 64Cu activity.

The complex decay scheme that makes 64Cu promising as both an imaging and therapeutic agent in medicine also makes the absolute measurement of its activity challenging. The National Institute of Standards and Technology (NIST) has completed a primary activity standardization of a 64CuCl2 solution using the 4πß(LS)-γ(NaI) live-timed anticoincidence (LTAC) counting method with a combined standard uncertainty of 0.51 %. Two liquid scintillation (LS) counting methods were employed for confirmatory measurements. Secondary measurements were made by high-purity germanium detectors, pressurized ionization chambers (IC), and a well-type NaI(Tl) counter. Agreement between the LTAC-based standard and standards from other laboratories was established via IC calibration factors. Poor agreement between methods and with theoretical IC responses may indicate a need for improved ß+/- branching probabilities and a better treatment of ß+/- spectra.

Improved calculations of electron capture transitions for decay data and radionuclide metrology.

Electron capture properties are crucial to establish the decay schemes of numerous radionuclides. The present modelling aims at improving the theoretical estimates of these decays, which are needed when no measurement is available. Allowed and forbidden unique transitions are calculated on the basis of precise relativistic wave functions of the atomic electrons, determined in previous work. In this context, correcting for atomic effects is of high importance. The two common approaches from Bahcall and Vatai to correct for the overlap and exchange effects have been extended to every subshell in a unified formulation, with the electron occupation precisely taken into account. The shake-up and shake-off effects, which create secondary vacancies, and the influence of the hole due to the capture process, have been considered. Uncertainties are also estimated. Relative capture probabilities and their ratios, including capture-to-positron ratios, have been found to be in good agreement with a selection of precise measurements. This modelling was then applied to the third forbidden unique transition of 40K decay, with an update of the recommended values for the branching ratios and the total decay half-life.

230U nuclear decay data evaluation.

The evaluation of the nuclear decay data of 230U, a radionuclide of interest in nuclear medicine (targeted alpha therapy), was performed within the Decay Data Evaluation Project (DDEP) and an IAEA Coordinated Research Project. The nuclear decay data presented are: the half-life, decay energy, alpha-particle emission energies and probabilities, internal conversion coefficients and gamma-ray energies and emission intensities. These new data, obtained using the DDEP methodology and software tools, will be included in the DDEP database NUCLEIDE.

Decay data for the positron emission tomography imaging radionuclide 124I: A DDEP evaluation.

A new decay data evaluation for the positron emitting radionuclide 124I has been performed using the Decay Data Evaluation Project (DDEP) methodology. New recommended values for the half-life, γ-ray emission probabilities, ß+ branching ratios, and other relevant nuclear and atomic data are provided. This paper provides a summary of the evaluation; the complete set of recommended data tables and detailed evaluator comments are available at the DDEP website.

Measurement of absolute γ-ray emission probabilities in the decay of 235U.

Accurate measurements were performed of the photon emission probabilities following the α decay of 235U to 231Th. Sources of highly enriched 235U were characterised in terms of isotopic composition by mass spectrometry and their activities were standardised by means of alpha-particle counting at a low defined solid angle. The standardised sources were subsequently measured by high-resolution γ-ray spectrometry with calibrated high-purity germanium detectors to determine the photon emission probabilities. Four laboratories participated in this work and reported emission probabilities for 33 γ-ray lines. Most of them agree with previously published evaluated data. In addition, new values are proposed for γ-lines which have been measured only once in the past.

Measurement of the electron capture probabilities of 55Fe with a metallic magnetic calorimeter.

The ratios of the electron capture probabilities PK, PL and PM of 55Fe have been measured with a metallic magnetic calorimeter, a specific type of cryogenic detector. The 55Fe source was enclosed in the detector absorber, whose dimensions were chosen such that the detection efficiency for Mn K X-rays was larger than 99.99%. Since all electrons and photons emitted by the source are absorbed in the detector, the detection efficiency is virtually 100% for K, L and M captures. The energy threshold was low enough to allow for clear separation of the M captures (~ 80eV) from noise. The capture probability ratios were translated to capture probabilities using the recommended value for the probability of the undetected N captures. The resulting values are in agreement both with the recommended values of PK, PL and PM and with the experimental data of Pengra and coworkers.

Direct measurement of alpha emission probabilities in the decay of 226Ra.

High-resolution alpha-particle spectrometry was performed to determine the main alpha-particle emission probabilities in the decay of 226Ra. Thin, homogeneous sources were prepared by electrodeposition on stainless steel disks. Alpha spectra with an energy resolution of 20keV were obtained in three laboratories and analysed with different deconvolution algorithms. In two set-ups, a magnet system was used to deflect conversion electrons to avoid their coincidental detection with the alpha particles. Spectra taken at close range without a magnet system yielded biased results which cannot be fully compensated by statistical corrections for coincidence summing. The derived emission probabilities of the three main alpha decays are 94.07 (1)%, 5.93 (1)%, and 0.0059 (15)%, respectively. They are in excellent agreement with calculated values derived from the P(γ+ce) decay scheme balance, which solves the existing discrepancy problem with two previous direct measurements published in literature.

Advancements in NORM metrology - Results and impact of the European joint research project MetroNORM.

The results of the three years European Metrology Research Programme's (EMRP) joint research project 'Metrology for processing materials with high natural radioactivity' (MetroNORM) are presented. In this project, metrologically sound novel instruments and procedures for laboratory and in-situ NORM activity measurements have been developed. Additionally, standard reference materials and sources for traceable calibration and improved decay data of natural radionuclides have been established.