In June 1944, Segrè was summoned into Oppenheimer's office and informed that while his father was safe, his mother had been rounded up by the Nazis in October 1943. Segrè never saw either of his parents again. His father died in Rome in October 1944. In late 1944, Segrè and Elfriede became naturalized citizens of the United States. His group, now designated R-4, was given responsibility for measuring the gamma radiation from the Trinity nuclear test in July 1945. The blast damaged or destroyed most of the experiments, but enough data was recovered to measure the gamma rays.