The positron decay partial half-lives of 143 PM and 144 PM are needed to assess the viability of elemental Pm as a cosmic-ray clock. We have conducted experiments to measure the β+ branches of these isotopes; we find β+ branches of < 5.7 x 10-6% for 143 Pm and < 8 x 10-5% for 144 Pm. Although these branches are a factor of 20 lower than the previous experimental limits the resulting partial half-lives are still to uncertain to permit any firm conclusions
