Exotic radionuclides from Accelerator Waste for Science and Technology - ERAWAST III: Half-life determination of pure electron capture nuclides (La-137, Tb-157)

• Applicant: Dr. Karsten Kossert
• Subject Area: Nuclear and Elementary Particle Physics, Quantum Mechanics, Relativity, Fields
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 450057137

In two previous projects (ERAWAST I and II) funded by the Swiss National Science Foundation (SNF) it was made clear that the lack of reliable nuclear decay data is astonishingly huge, in particular for half-lives of relatively long-lived radionuclides. In general, half-lives are relevant for applications in nuclear medicine and industry, and several research fields (e.g. environmental and climate research, Earths and Solar sciences) require accurate data.A research group at PSI has gained access to a considerable number of sources for long-lived radionuclides and developed extraordinary experience in radiochemical separation and purification techniques over the last 15 years. Based on this, measurements of several radionuclides were possible and unique results were obtained.With the present proposal (SNF Lead Agency + DFG), we shift the focus to the half-life determination of the first two examples of pure electron capture lanthanide isotopes: 137La and 157Tb. The half-life measurements for these two radionuclides are extremely challenging and strongly depend on the quality of the sample. In particular, samples must not contain any other radiation-emitting isotope and the measurement of the number of atoms requires a reliable method for estimating the contribution of possible isobars. Moreover, transition probabilities and de-excitation spectra shapes of these two isotopes are not well-known, which increases the uncertainty of the activity measurement accordingly. Improvement could be achieved by measuring these spectra with a novel kind of detectors, Magnetic Metallic Calorimeters (MMC), which are currently being explored in several metrology groups. Dedicated sample preparation procedures have to be developed to make this kind of detectors applicable in the future. The following tasks have to be fulfilled:• Purification of the 137La sample, which was obtained in the frame of ERAWAST II.• Separation of 157Tb from irradiated enriched 156Dy. Purification of the sample.• Activity determination using Liquid Scintillation Counting with uncertainty < 5% (to be performed by PTB)• Determination of the number of atoms by ICP-MS with uncertainty < 2%, considering correction of the isobar contribution.• Exploring sample deposition procedures for MMCs.Precision measurements with high accuracy and low uncertainties meet urgent requirements from nuclear data communities, metrology groups and related science. With this two-year program, we hope to pave the way for a long-lasting program for sample preparation and development of front-end measurement techniques for long-lived, “hard-to measure” isotopes after the retirement of the PI (D. Schumann) in 2023.

• DFG Programme: Research Grants
• International Connection: Switzerland
• Cooperation Partner: Dr. Dorothea Schumann