2011.07.024. Horvath, David G.; et al. Evidence for geologically recent explosive volcanism in Elysium Planitia, Mars. 11 November 2020. arXiv:2011.05956v1
use. 228Ac is used as an indicator of radioactivity in chemical research, as it emits high-energy electrons (2.18 MeV) that can be easily detected. 228Ac-228Ra