Niels Henrik David Bohr (October 7, 1885 - November 18, 1962) was a Danish physicist who made foundational contributions to understanding atomic structure and quantum mechanics, for which he received the Nobel Prize in Physics in 1922. Bohr published his model of atomic structure in 1913 wherein he introduced the theory of electrons traveling in orbits around the atom's nucleus, the chemical properties of each element being largely determined by the number of electrons in the outer orbits of its atoms. He also introduced the idea that an electron could drop from a higher-energy orbit to a lower one, in the process emitting a photon (light quantum) of discrete energy. This became a basis for quantum theory. Bohr mentored and collaborated with many of the top physicists of the century at his institute in Copenhagen. He was part of the British team of physicists working on the Manhattan Project where he was known by the name of Nicholas Baker for security reasons. His role on the project was as consultant. Following the war Bohr returned to Copenhagen where he died in 1962 of heart failure.