Unbitrium

Unbitrium (), also known as eka-protactinium or element 123, is the possible chemical element in the periodic table that has the temporary symbol Ubt and has the atomic number 123. Calculations have shown that 326Ubt would be the most stable isotope. The closed neutron shells say that 307Ubt and 319Ubt would be the most stable isotopes. 
As of February 2021, no attempt has ever been made to make element 123.
Naming.
The name unbitrium is a systematic element name, used as a placeholder until it is confirmed by other research groups and the IUPAC decides on a name. Usually, the name suggested by the discoverer(s) is chosen.
Synthesis.
This reaction would create 307Ubt, which is expected to be relatively stable.
 + → + 3 n 
Fictional reference to element 123.
In the fictional universe of "", this element was seemingly discovered and named. The episode "Rascals" depicted a "trans-periodic table," in a schoolroom set, which depicted element number 123 as being named jamesium, symbol Rj, having an atomic weight of 326. The graphic was created by set artists, probably a homage to designer Richard D. James, and listed this element in the fictional "gamma series."
In the third episode of season one of the television series "Agents of S.H.I.E.L.D." element 123 is depicted 24 minutes in as the element Gravitonium, atomic weight 308