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

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.

Status of the decay data for medical radionuclides: existing and potential diagnostic γ emitters, diagnostic β+ emitters and therapeutic radioisotopes

Recommended half-lives and specific well-defined emission energies and absolute emission probabilities are important input parameters that should be well-defined to assist in ensuring the diagnostic and therapeutic efficacy of individual radionuclides when applied in the field of nuclear medicine. Bearing in mind the nature of these requirements, approximately one hundred radionuclides have been considered and re-assessed as to whether their decay data are either adequately quantified, or require further in-depth measurements to improve their existing status and merit full re-evaluations of their decay schemes. The primary aim of such a review is to provide sufficient information on the existing and future requirements for such atomic and nuclear data.

Development of a fast characterization setup for radionuclide generators demonstrated by a 227Ac-based generator

The development of a setup for a fast online characterization of radionuclide generators is reported. A generator utilizing the mother nuclide 227Ac sorbed on a cation exchange resin is continuously eluted by using a peristaltic pump. To allow continuous and pulse-free elution of a large volume over extended time periods a 3D-printed interface designed to remove pressure-oscillations induced by the pump was placed between pump and generator column to ensure undisturbed generator elution. The eluate of the generator is passed through a 3D printed flow cell placed inside a borehole Na(Tl)-scintillation detector for high counting efficiency. Alternatively, a HPGe detector suitable for nuclide identification was used to demonstrate the validity of the online method. The detection system combines conventional gamma-ray spectrometry with fast list mode data acquisition in the Matlab software package. Elution experiments were performed at different flow rates of hydrochloric acid, separating 211Bi (t 1/2 = 2.14 min) free from its parent nuclides. In addition, to prove the versatility of the setup, experiments at different hydrochloric acid concentrations were performed resulting in the elution of pure 211Pb (t 1/2 = 36.1 min) and 223Ra (t 1/2 = 11.43 d), respectively.

A new evaluation of the nuclear decay data of 223Ra

Since 2013, the radionuclide 223Ra is used in nuclear medicine to prepare radiopharmaceuticals for targeted radiotherapy. 223Ra is a member of the natural radioactive series of actinium and decays by alpha-particle emission, populating the excited levels of 219Rn. According to the 2011 nuclear decay data evaluation within the Decay Data Evaluation Project (DDEP), by V.P. Chechev, the half-life of 223Ra is (11.43 ± 0.03) days. The decay scheme is not considered as fully complete, because of the disagreement between the measured and calculated probabilities of some alpha-transitions and incomplete information on several gamma-ray transitions. New high quality measurements of 223Ra nuclear decay data were performed and numerous results were published since 2012 and, consequently, an updated nuclear decay data evaluation was undertaken, according to the DDEP procedures. The main results obtained, focusing on the recommended data improvements, are presented and discussed in this paper.