Friedlander, who was Jewish, escaped Nazi Germany. He was also an abortion-rights activist, pushing in the 1960s for the legalization of abortion in New York State, and later serving as president of Planned Parenthood Long Island.
Friedlander, a member of the National Academy of Sciences and an amateur dessert chef renowned for his holiday cookies, died of coronary heart disease, his wife said.
"He was one of the kindest people that ever was - thoughtful, fair, open," recalled his wife, Barbara Strongin, 74, of South Setauket. "He saw the big picture."
Born Gerhart Friedlaender in 1916, he was forbidden by the Nazi government to attend university, so he trained as a laboratory technician before fleeing to the United States in 1936.
A Jewish refugee organization offered him a scholarship to enroll at the University of California at Berkeley, where he completed his bachelor of science degree, earned a doctorate in chemistry and met his first wife, with whom he had two daughters.
Friedlander, who changed the spelling of his name when he became an American citizen, worked at Los Alamos on the development of the atomic bomb from 1943 to 1946. There, he wrote a seminal textbook on an emerging field of science. "Nuclear and Radiochemistry" is still in circulation today.
He later signed a petition to President Ronald Reagan from former Manhattan Project scientists urging nuclear disarmament.
"The fact that they dropped a second bomb [at Nagasaki] was awful to him," Strongin said. "Nuclear science isn't bad. It's how people use it and threaten it that's bad."
Friedlander joined Brookhaven National Lab in 1948, leading research in high-energy nuclear reactions.
With colleagues in the United States and abroad, he pioneered the development of computerized calculations of nuclear reaction mechanisms, helping to formulate theoretical models that are still used today.
He played a leading role in advocating for and preparing the gallium solar-neutrino experiment known as GALLEX in the Gran Sasso Underground Laboratory in Italy.
Friedlander was moved by the death of his first wife, Gertrude Maas, in a car accident, to take up the cause of women's rights, joining the National Organization for Women and NARAL, a national abortion-rights group.
Serving on the board of Planned Parenthood Long Island, he met Barbara Strongin, who was hired as the group's chief executive.
They married in 1983.
Together, they built a house in Smithtown, advocated for women's rights, and baked cookies.
"For 28 years, we had a very good life together," she said. The couple later moved to Setauket.
In addition to his wife, Friedlander is survived by his daughters, Ruth Huart, 66, of Écoust St. Mein, France, and Joan Hurley, 64, of Agoura, Calif.; four grandchildren; and two great-grandchildren.
Private services have been held. The family is planning a public memorial.