Fifty years after the birth of the atomic bomb, the country prepares to commemorate the act that brought World War II to an end. For me, the public debate over the bombing of Hiroshima and Nagasaki mirrors a private one: For most of my life, the bomb has been a personal matter.

During World War II, my father, Harry Palevsky, was an electrical engineer on the Manhattan Project, the massive effort of American academia, government and industry that produced the world's first nuclear weapon. He met my mother, Elaine Sammel, who had an undergraduate degree in physics, while they worked on the project at the University of Chicago's Metallurgical Laboratory. They later transferred to the top-secret Los Alamos laboratory in New Mexico, where my father worked on the trigger mechanism that detonated the bomb. My mother worked on the development of optical instrumentation. On a hot day in the summer of 1945, they drove down the mountain to Santa Fe and got married.

In 1990, I was caring for my father after my mother's sudden death. He had been chronically ill for many years, and in the months before he died I began interviewing him about his life and work for a book of memoirs. One morning when he was talking about the Manhattan Project, I asked what it had been like at Los Alamos after the successful bombing of Hiroshima. My father replied that there had been a lot of mixed feelings among the scientists. Then he hung his head and fell silent.

After a long pause, he looked up at me. With a sob caught in his throat, he asked, "Did you know that Nagasaki was the center of Christianity in Japan?" I said I didn't.

I cannot tell exactly when my father first questioned the decision to use the atomic bomb, but I had long known of his contradictory feelings about his work on the Manhattan Project. One one hand, it had been a prelude to his career in the field he loved, nuclear physics. But although he felt privileged to have worked alongside some of the century's greatest scientists to end the war, he was deeply troubled by the terror they created to achieve peace. At that moment, when my father openly shared his grief with me, I felt his effort to reconcile the moral complexities of the bomb was being passed on to me. When he died, it became his legacy.