TRUE

The first nuclear weapons were fission bombs developed by the United States during the Manhattan Project and first tested in July 1945 (1.1.6, 1.3.7). These weapons function through nuclear fission, a process where the nucleus of a heavy, unstable atom such as uranium-235 or plutonium-239 is split into smaller fragments after absorbing a neutron (1.3.2, 1.4.3). This reaction results in a mass defect where the total mass of the resulting fragments is slightly less than the original mass of the starting materials (1.4.2). According to Albert Einstein’s mass-energy equivalence formula, E=mc2, this lost mass is converted into a colossal release of kinetic energy and radiation (1.4.6, 1.4.9). While later thermonuclear weapons use fusion, the original atomic bombs relied entirely on this splitting mechanism to achieve their explosive yield (1.1.6, 1.2.5).