First Direct Measurements of Superheavy-Element Mass Numbers

Author(s): Gates, JM; Pang, GK; Pore, JL; Gregorich, KE; Kwarsick, JT; Savard, G; Esker, NE; Kireeff Covo, M; Mogannam, MJ; Batchelder, JC; Bleuel, DL; Clark, RM; Crawford, HL; Fallon, P; Hubbard, KK; Hurst, AM; Kolaja, IT; Macchiavelli, AO; Morse, C; Orford, R; Phair, L; Stoyer, MA | Abstract: © 2018 American Physical Society. An experiment was performed at Lawrence Berkeley National Laboratory's 88-in. Cyclotron to determine the mass number of a superheavy element. The measurement resulted in the observation of two α-decay chains, produced via the Am243(Ca48,xn)291-xMc reaction, that were separated by mass-to-charge ratio (A/q) and identified by the combined BGS+FIONA apparatus. One event occurred at A/q=284 and was assigned to Nh284 (Z=113), the α-decay daughter of Mc288 (Z=115), while the second occurred at A/q=288 and was assigned to Mc288. This experiment represents the first direct measurements of the mass numbers of superheavy elements, confirming previous (indirect) mass-number assignments.