Martin 4-0-4 N40409 (cn 14113) was used by EG&G (Atomic Energy Commission contractor) to monitor the Nevada Test Site in 1967-77
Las Vegas Airport, September 26, 1974:
Computer PDP-11(?) and radiation emissions monitoring equipment:
N40409 and Beech Twin Bonanza N702B (another aircraft operated by EG&G) at Las Vegas Airport, 1968:
Bonus:e piece of Cold War history: many thanks for posting!