Ben Roy Mottelson, an American-Danish theoretical physicist who shared a Nobel Prize for revealing how the motion of protons and neutrons could distort the shape of the nuclei of atoms, died on May 13. He was 95.

Dr. Mottelson was awarded the Nobel in physics in 1975 along with James Rainwater, a Columbia University physicist, and Aage Bohr, a Danish scientist whose father, Niels Bohr, was awarded the Nobel in physics in 1922.

The three scientists’ discoveries about the nuclei of atoms had an impact on the development of human-made nuclear fusion, which generates energy by combining hydrogen atoms. Dr. Mottelson and Dr. Bohr later expanded their work, publishing two encyclopedic books, Nuclear Structure: Single Particle Motion, and Nuclear Structure: Nuclear Deformations. The books remain standard references.