Samuel T. Cohen, the physicist who invented the small tactical nuclear weapon known as the neutron bomb, a controversial device designed to kill enemy troops with subatomic particles but leave battlefields and cities relatively intact, died on Sunday at his home in Los Angeles. He was 89.

The cause was complications of stomach cancer, his son Paul said.

Unlike J. Robert Oppenheimer and Edward Teller, the respective fathers of the atomic and hydrogen bombs, Mr. Cohen was not well known outside government and scientific circles, although his work for years influenced the international debate over the deployment and potential uses of nuclear arms.

In contrast to strategic warheads, which can kill millions and level cities, and smaller short-range tactical nuclear arms designed to wipe out battlefield forces, the neutron bomb minimized blast and heat. Instead, it maximized a barrage of infinitesimal neutrons that could zip through tanks, buildings and other structures and kill people, usually by destroying the central nervous system, and all other life forms.

While doubters questioned the usefulness, logic and ethics of killing people and sparing property, Mr. Cohen called his bomb a “sane” and “moral” weapon that could limit death, destruction and radioactive contamination, killing combatants while leaving civilians and towns unscathed. He insisted that many critics misunderstood or purposely misrepresented his ideas for political, economic or mercenary reasons.