Measurements of the half-life of 214Po and 218Rn using digital electronics

Activity standardization and half-life measurement of 177Lu

The activity of the ¹⁷⁷Lu solution has been measured by means of the CIEMAT/NIST efficiency tracing method. This result has been compared to the previous obtained results received from 4πβ(LS)-γ coincidence and anticoincidence counting. The activities determined with various methods have been found to be consistent. The decay curve of the ¹⁷⁷Lu solution has been followed in the TDCR counter to determine the half-life of this isotope. The half-life has been separately determined for double and triple coincidence events. The arithmetic mean value of these two results has been found to be T_1/2 = 6.6489(52) d.

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.

Radionuclide metrology: confidence in radioactivity measurements

Radionuclides, whether naturally occurring or artificially produced, are readily detected through their particle and photon emissions following nuclear decay. Radioanalytical techniques use the radiation as a looking glass into the composition of materials, thus providing valuable information to various scientific disciplines. Absolute quantification of the measurand often relies on accurate knowledge of nuclear decay data and detector calibrations traceable to the SI units. Behind the scenes of the radioanalytical world, there is a small community of radionuclide metrologists who provide the vital tools to convert detection rates into activity values. They perform highly accurate primary standardisations of activity to establish the SI-derived unit becquerel for the most relevant radionuclides, and demonstrate international equivalence of their standards through key comparisons. The trustworthiness of their metrological work crucially depends on painstaking scrutiny of their methods and the elaboration of comprehensive uncertainty budgets. Through meticulous methodology, rigorous data analysis, performance of reference measurements, technological innovation, education and training, and organisation of proficiency tests, they help the user community to achieve confidence in measurements for policy support, science, and trade. The author dedicates the George Hevesy Medal Award 2020 to the current and previous generations of radionuclide metrologists who have devoted their professional lives to this noble endeavour.

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 T_1/2Np237,E=59.54keV=67.86±0.09ns, T_1/2Pa233,E=86.47keV=36.44±0.10ns and T_1/2Ac227,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.

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 4πβ(LS)-γ anticoincidence counting. The measurements were carried out in a custom-built, combined TDCR / 4πβ(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.

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.

Optical detection of radon decay in air

An optical radon detection method is presented. Radon decay is directly measured by observing the secondary radiolumines cence light that alpha particles excite in air, and the selectivity of coincident photon detection is further enhanced with online pulse-shape analysis. The sensitivity of a demonstration device was 6.5 cps/Bq/l and the minimum detectable concentration was 12 Bq/m³ with a 1 h integration time. The presented technique paves the way for optical approaches in rapid radon detec tion, and it can be applied beyond radon to the analysis of any alpha-active sample which can be placed in the measurement chamber.

Half-lives of 221Fr, 217At, 213Bi, 213Po and 209Pb from the 225Ac decay series

The half-lives of (221)Fr, (217)At, (213)Bi, (213)Po, and (209)Pb were measured by means of an ion-implanted planar Si detector for alpha and beta particles emitted from weak (225)Ac sources or from recoil sources, which were placed in a quasi-2π counting geometry. Recoil sources were prepared by collecting atoms from an open (225)Ac source onto a glass substrate. The (221)Fr and (213)Bi half-lives were determined by following the alpha particle emission rate of recoil sources as a function of time. Similarly, the (209)Pb half-life was determined from the beta particle count rate. The shorter half-lives of (217)At and (213)Po were deduced from delayed coincidence measurements on weak (225)Ac sources using digital data acquisition in list mode. The resulting values: T1/2((221)Fr)=4.806 (6) min, T1/2((217)At)=32.8 (3)ms, T1/2((213)Bi)=45.62 (6)min, T1/2((213)Po)=3.708 (8) μs, and T1/2((209)Pb)=3.232 (5)h were in agreement only with the best literature data.

Decay data measurements on 213Bi using recoil atoms

In this work, (213)Bi has been separated from an open (225)Ac source by collecting recoil atoms onto a glass plate in vacuum. The activity of such recoil sources has been measured as a function of time, using an ion-implanted planar Si detector in quasi-2π geometry. From these measurements, a new half-life value of T1/2((213)Bi)=45.62 (6)min was derived. Additionally, high-resolution alpha-spectrometry measurements were performed at a solid angle of 0.4% of 4πsr, to verify the energies and emission probabilities of the α-emissions from (213)Bi. Using (225)Ac, (221)Fr, (217)At and (213)Po peaks as reference peaks, the measured (213)Bi α-peak energies at Eα,0=5878 (4)keV and Eα,1=5560 (4)keV were about 10keV higher than validated data. The relative α-particle emission probabilities of (213)Bi, Pα,0=0.9155 (11) and Pα,1=0.0845 (11), and the (213)Bi alpha branching factor, Pα=1-Pβ=2.140 (10)%, are compatible with recommended values, but have a higher accuracy.

Measurement of the 225Ac half-life

The (225)Ac half-life was determined by measuring the activity of (225)Ac sources as a function of time, using various detection techniques: α-particle counting with a planar silicon detector at a defined small solid angle and in a nearly-2π geometry, 4πα+β counting with a windowless CsI sandwich spectrometer and with a pressurised proportional counter, gamma-ray spectrometry with a HPGe detector and with a NaI(Tl) well detector. Depending on the technique, the decay was followed for 59-141 d, which is about 6-14 times the (225)Ac half-life. The six measurement results were in good mutual agreement and their mean value is T(1/2)((225)Ac)=9.920 (3)d. This half-life value is more precise and better documented than the currently recommended value of 10.0 d, based on two old measurements lacking uncertainty evaluations.