Bernard L. Cohen, professor emeritus of physics at the University of Pittsburgh, never stopped learning.

This semester, at the age of 87, he began sitting in on an astronomy class in anticipation of teaching it in the future, but pancreatic cancer intervened. He died March 17.

Mr. Cohen, who lived much of his life in Squirrel Hill, was known for believing that the dangers of low-level radiation were overblown, bringing the importance of home radon testing to the forefront, supporting nuclear energy and working on the structure of cell nuclei.

His honors included the Tom W. Bonner Prize in Nuclear Physics in 1981 from the American Physics Society, the highest award for a nuclear physicist.

"He was an extraordinarily good scientist," said James Maher, distinguished service professor of physics, senior science adviser and provost emeritus at Pitt. "He was a very gentle, kind person, but he always said what he thought."

In the 1980s, Mr. Cohen wrote about challenging Ralph Nader, who maintained that plutonium is dangerous.

In an effort to show that plutonium wasn't as dangerous as some think, Mr. Cohen offered to ingest as much plutonium as Mr. Nader would caffeine, a challenge that wasn't accepted.

Mr. Maher said that Mr. Cohen "thought the risks of running nuclear plants were not as great as the risks we experience burning coal."

Mr. Cohen was a native of Pittsburgh and served as an engineering officer in the Navy in the Pacific during World War II before completing his undergraduate work at Case Institute of Technology, now known as Case Western Reserve University, in 1944.

He earned a master's degree from Pitt in 1947 and a doctorate from what is now Carnegie Mellon University in 1950.

He and his late wife, Anna Foner Cohen, to whom he was married for 48 years until her death in 1998, both earned doctorates in physics the same year from CMU, said their daughter, Judith Cohen of Squirrel Hill.

The couple worked together on the project to detect radon in homes, she said.

Mr. Cohen worked at the Oak Ridge National Laboratory from 1950 to 1958, after which he joined the Pitt faculty as an associate professor of physics and chemistry. Mr. Cohen, who became a professor in 1961, held adjunct appointments at Pitt in chemical and petroleum engineering, radiation health, and environmental and occupational health.

He also was director of Pitt's Scaife Nuclear Laboratory from 1965 to 1978.

When he retired in 1994, he became professor emeritus of physics.

Ms. Cohen said family life was important to her father and included many travels together to international conferences.

Mr. Cohen also is survived by three sons, Donald of Los Angeles; Fred of Livermore, Calif.; and Ernie of Philadelphia; 10 grandchildren; two great-grandchildren; and his companion, Ann Ungar of Squirrel Hill.

Interment was in the West View Cemetery of Rodef Shalom Congregation.

First Published: March 29, 2012, 4:00 a.m.