Physicist Enrico ___ (5)
I believe the answer is:
fermi
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">physicist enrico</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for fermi that I've seen before include "Enrico -----, Italian nuclear physicist (1901-1954); in the US from 1939" , "Enrico, Italian Nobel prize physicist" .)