After receiving his Ph.D., he became a group leader at the Fermi Institute for Nuclear Studies at the University of Chicago and also took up a position at the Air Force Cambridge Research Laboratory in Bedford, Massachusetts. He managed radiation-effects projects studying a series of nuclear weapons tests in Nevada and the 1954 hydrogen bomb tests at the Bikini Atoll in the South Pacific.
In 1962, after witnessing the devastating effects of nuclear weapons, Martell decided to pursue a different direction in his life and took up a position as a radiochemist in the Atmospheric Chemistry Division at NCAR in Boulder, Colorado.
In 1980 he published a paper in Newscript in which he argued that radium progeny, particularly polonium-210, are responsible for the cancer-causing effects of cigarettes. He followed this up in 1983 with a [http://www.pnas.org/cgi/content/abstract/80/5/1285 subsequent research paper] in which he calculated that smokers who die of lung cancer have been exposed to 80-100 rads of radiation.
In 1993 he published a paper in which he theorized that ionizing radiation in artesian groundwater was the energy source which fueled the evolution of DNA and the first living cells, after exchanging ideas with the University of Colorado's Nobel prize-winning chemist Tom Cech. At the time of his death, he was working on a book called "Natural Radionuclides and Life".