Shorter half-life of p-process 146Sm measured and 146Sm/142Nd chronology of the Solar System

N. Kinoshita, University of Tsukuba
M. Paul, Hebrew University of Jerusalem
Y. Kashiv, University of Notre Dame
P. Collon, University of Notre Dame
D. Robertson, University of Notre Dame
C. Schmitt, University of Notre Dame
X. D. Tang, University of Notre Dame
B. DiGiovine, Argonne National Laboratory
J. P. Greene, Argonne National Laboratory
D. J. Henderson, Argonne National Laboratory
C. L. Jiang, Argonne National Laboratory
S. T. Marley, Argonne National Laboratory
R. C. Pardo, Argonne National Laboratory
K. E. Rehm, Argonne National Laboratory
R. Scott, Argonne National Laboratory
R. Vondrasek, Argonne National Laboratory
C. Deibel, Argonne National Laboratory
T. Nakanishi, Kanazawa University
A. Yokoyama, Kanazawa University


The short-lived nuclide 146Sm, synthesized in stellar events by the p-process and now extinct in the Solar System, serves as both an astrophysical and geochemical chronometer through measurements of isotopic anomalies of its α-decay daughter 142Nd. Using artificially produced 146Sm via 147Sm(γ,n), 147Sm(n, 2n) and 147Sm(p,nε) reactions, we performed a new measurement of the 146Sm half-life by measuring the 146Sm/ 147Sm alpha activity with a Si surface barrier detector and the 146Sm/147Sm atom ratio with accelerator mass spectrometry (AMS). Our result, t114/62 = 68 ± 7 (1σ) million years (My), is significantly shorter than the adopted value (103 ± 5 My). The shorter 146Sm half-life value implies a higher initial Solar System ratio, (146Sm/144Sm)0 = 0.0094 ± 0.0005 (2σ), than the recently derived value 0.0085 ± 0.0007(2σ). The time interval between isolation of the Solar Nebula from the interstellar medium and formation of the first solids, is reduced by a factor of ∼2.5 to 20 from previous estimates. Early planetary mantle differentiation processes on Earth, the Moon and Mars dated by 146Sm-142Nd converge to a shorter time span, due to the combined effect of the new 146Sm half-life and (146Sm/144Sm)0 values. © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence.