He proposed a corpuscular model of radiation as the photoelectric mechanism. This German stamp shows electrons escaping at random angles while light strikes the surface. Inside the mushroom cap appears a beryllium atom with four electrons orbiting a nucleus of four protons and five neutrons.
Beryllium is a highly efficient generator of neutrons when bombarded with alpha particles.
It may serve as a source of neutrons to initiate the nuclear fission within the fuel nucleus of a reactor. At the base of the mushroom are roiling, churning clouds of debris as seen on actual photos of nuclear events. However, front and center in the picture is a prone white-draped figure being irradiated from upper left, watched by a technician behind a window to the right. This peaceful application of nuclear energy somewhat mitigates the stark symbolism of the mushroom cloud. This German stamp commemorates two Nobel laureates, friends for life, and expatriates.