In Memoriam: Hans Geissel (1950–2024).

Hans Geissel, a pioneer in radioactive ion beams, passed away on April 29, 2024. His career was closely tied to the development of the GSI Helmholtz-Center for Heavy-Ion Research in Germany, which laid the foundation for the Facility for Antiproton and Ion Research (FAIR). Geissel's work had a global impact and he made significant contributions to the field of nuclear physics, atomic physics, and ion optics. He was involved in the discovery of many exotic nuclei, the development of simulation programs, and the advancement of fragment separator facilities worldwide. Geissel received numerous awards for his groundbreaking work and was known for his international collaborations and openness to new ideas. [Extracted from the article]