New AMS method to measure the atom ratio 146Sm/147Sm for a half-life determination of 146Sm

The extinct p-process nuclide 146Sm (t1/2 = 103 ± 5 Myr) is known to have been present in the Early-Solar System and has been proposed as an astrophysical chronometer. 146Sm is also intensely used to date meteorite and planetary differentiation processes, enhancing the importance of an accurate knowledge of the 146Sm half-life. We are engaged in a new determination of the 146Sm half-life in which the 146Sm/147Sm atom ratio is determined by accelerator mass spectrometry at the ATLAS facility of Argonne National Laboratory. In order to reduce systematic errors in the AMS determination of the 146Sm/147Sm ratios (in the range of 10−7–10−9), 146Sm and 147Sm ions were alternately counted in the same detector in the focal plane of a gas-filled magnet, respectively in continuous-wave and attenuated mode. Quantitative attenuation is obtained with the 12 MHz pulsed and ns-bunched ATLAS beam by chopping beam pulses with an RF sweeper in a ratio (digitally determined) down to 1:106. The experiments and preliminary results are discussed.