Redefining the Geologic Timescale of the Solar System by Accurately Determining the Half-Life of Samarium-146 with Magnetic Microcalorimeters

Geonbo Kim | 20-LW-024

Project Overview

146Sm is used for determining the ages of major events in the early solar system, as its half-life (68 Ma–103 Ma) is similar to the length of solar system formation. The half-life of 146Sm is therefore the key nuclear parameter in Sm–Nd chronometry and for understanding the history of the early Solar System. However, there are two published values of 687 Ma and 1031 Ma that differ by app[roximately 30%, causing significant uncertainties in Sm–Nd chronometry.

In this project, the half-life of 146Sm is re-measured using state-of-the-art technologies. First, an ultra-pure 146Sm sample is produced by a novel approach. Pure 146-isobars are produced and collected by tantalum-target spallation and mass-separators at the TRIUMF Laboratory in Canada. Then a pure 146Sm sample was extracted from the 146-isobar sample by chemical-separation procedures that are well-established at the LLNL for chosmo-chemistry research. Second, the total number of 146Sm atoms in the sample was quantified using isotope-dilution thermal ionization mass-spectrometry (ID-TIMS) that is also well-established for cosmo-chemistry research at LLNL. Third, the quantified sample is embedded in a gold foil for accurate activity measurement via cryogenic decay energy spectrometry (DES) using magnetic microcalorimeters. DES has excellent performance in activity quantification due to its 100% detection efficiency and ultra-high energy resolution features. Finally a second ID-TIMS measurement was performed to to confirm that the total number of 146Sm atoms remain same during entire experimental procedures. Systematic uncertainties are carefully investigated by multiple independent analyzers and using multiple dataset with independent setup. The new half-life of 146Sm has been obtained by combining the activity and the number of 14 146Sm atoms, using the equation, where T is the half-life, N is the total number of atoms, and A is the activity. Total uncertainties were 0.7% for statistical uncertainty and 0.5% for systematical uncertainty; the combined uncertainty was 0.8%. The final half-life number is not posted herein.

Mission Impact

The main outcome of this project (i.e., the improved 146Sm half-life and the improved Sm–Nd chronometry uncertainty) will benefit LLNL's cosmochemistry and astrophysics programs that use the Sm–Nd chronometers for cosmo-chronology research. Another technical outcome is the advancement of the decay energy spectrometry (DES) technique. DES is a promising technology in various nuclear applications and fundamental science research. Based on the advancement of the DES technology in the 20-LW-024 LDRD project, several new programs and projects were initiated. They are (1) development of DES for nuclear material analysis for international nuclear safeguards (IAEA) that is supported by NNSA NA-241 office, (2) validation of DES technology with IAEA safeguards samples and building an end-user instrument for deployment at IAEA NML (nuclear material laboratory) that is supported by US support program (USSP), and (3) DES development for post-detonation forensics for rapid response that is supported by NNSA NA-22. The sapphire-based detector that is developed in this 20-LW-024 project yielded a new procedure for using diamond crystal detectors for dark matter detection, which was funded by FS LDRD in FY22 and now funded by DOE HEP R&D program in FY23.

DES development advanced "Analytical chemistry and forensics science" and "Physics at the frontier" that are the priority R&D areas in the core competency "Nuclear, Chemical, and Isotopic S&T" in the publication "Investment Strategy for Science and Technology 2022". Also, it advanced quantum information science and radiation detection that are cross-cutting investment areas of the NACS division in 2022.

Publications, Presentations, and Patents

Shollenberger, Q. R., et al., 2022. "Chemical Separation of 146Sm for Half-Life Determination." Journal of Radioanalytical and Nuclear Chemistry (2022): 1-7.

Kavner, A. R. L., et al., 2022. "Study of Pile-Up Effects in Decay Energy Spectroscopy." Journal of Low Temperature Physics (2022): 1-9.

Kim, G. B., et al., 2022. "Absolute Decay Counting of $$^{146} $$146 Sm and $$^{147} $$147 Sm for Early Solar System Chronology." Journal of Low Temperature Physics (2022): 1-8.

Kavner, A.R.L. and G.-B. Kim, 2022. "New Measurement of the 146Sm & 147Sm Half-Lives using High Resolution 4π Microcalorimeters." 15th International Conference on Nuclear Data for Science and Technology (ND2022). Virtual. July 2022.

Zhang, X. et al., 2022. "Searching for a keV Sterile Neutrino via 241Pu Beta Spectrum." 30th Conference on Neutrino Physics and Astrophysics, Seoul, Republic of Korea. June 2022.

Kim, G. B., 2022. "Decay Energy Spectrometry (DES) for Samarium Chronometry and Nuclear Material Analysis", 12th International Conference on Methods and Applications of Radioanalytical Chemistry (MARC), Kailua-Kona, HI. April 2022.

Kavner, A. R. L. et al., 2021. "Systematic Effects of Pile-up in Cryogenic Decay Energy Spectroscopy." 19th International Workshop on Low Temperature Detectors 209: 1070-1078 (2021).

Kim, G. B. et al., 2021. "Determining the Controversial Sm-146 Half-Life Using Metallic Magnetic Calorimeters for Early Solar System Chronology." 19th International Workshop on Low Temperature Detectors 209. July 2021.

Kavner, A. R. L. et al., 2021. "A Novel Approach using Sapphire Crystals and Magnetic Microcalorimeters for Nuclear Material Analysis." USDOE National Nuclear Security Administration. Virtual. LLNL-CONF-820590.