Decay Chains of Fast Alpha Emitters in the Actinide Region

Abstract: With the advent of increasingly advanced spectroscopic instruments after the turn of the century, it has become accessible to unravel the structure of instantly ‘vanishing’ nuclei, with lifetimes as short as 1 μs, and responsible for pile-up events in analog electronics. Experimental data has been recorded by the Nuclear Structure Group at Lund University for 48Ca/50Ti + nat.Hf reactions during the preparation stages of the ‘Spectroscopy along Decay Chains of Element 114, Flerovium’ which was carried out in two subexperiments in 2019 and 2020 at the GSI Helmholtz Centre for Heavy Ion Research in Darmstadt, Germany. These reactions have yielded hints of spectroscopic information for fast α-decaying nuclei in anticipated long α-decay chains in the actinide region. Many of these nuclei have not been studied in detail since their discovery decades earlier. This work adds new indications which contribute to the nuclear structure information for some of these fast α emitters. The investigated region of the nuclidic chart is in the vicinity of heavy-, neutron-deficient isotopes normally considered a stepping stone for answering open questions of how approaching the N = 126 shell closure affects the nuclear structure of isotopes in this region. The recorded data was prepared to implement a decay-chain-hunting procedure. Comprehensive data analysis has been carried out to deduce the decay chains of the several, fast α emitters lying in the region of the neutron-deficient uranium isotopes. The most prevalent decay chain seen is that of the 225U isotope of which all four α decays are observed and a decay scheme including α-decay fine structure has been produced. This acted as a proof-of-concept technique for further searches. More importantly, there are strong indications of possibly two new states as well as an improved half-life of 217Ra. Some of the very fast α decays have been observed successfully. Lastly, indications of a handful of new excited levels have been found. Building on the work done in this project is expected to lead to exciting findings that would increase our knowledge and understanding of the nuclear structure of these fast α-decaying isotopes.