Felix Hans Boehm

Eminent nuclear experimentalist Felix Hans Boehm passed away on 25 May 2021, a few days before his 97th birthday. His scientific career spanned the second half of 20th century and coincided with evolution experimental physics—from “in-house,” relatively small-scale experiments performed by handful physicists to large-scale efforts at an external facility significant group participants. Those massive undertakings require long costly preparations substantial running times. made contributions each stage that evolution.Felix BoehmPPT|High resolutionFelix was born 9 June 1924 in Basel, Switzerland. He received undergraduate degree from University Geneva PhD physics ETH Zürich. Paul Scherrer thesis supervisor, Wolfgang Pauli taught him theoretical member Felix’s exam committee. During student days, interested electrophysiology, among other things, able collaborate Walter Hess, who later became Nobel laurate for physiology.After short stint ETH, crossed Atlantic work Columbia Chien-Shiung Wu, affectionately known as Madame Wu. In 1953 moved Caltech, where he spent next century. It exciting time: 1956 parity violation weak interactions proposed experimentally verified. several collaborators, primarily Aaldert Wapstra, were quickly set up new apparatus observe beta decays, thus confirming Wu’s initial findings.Felix’s undertaking show is also violated electromagnetic transitions, consequence current–current structure Murray Gell-Mann Richard Feynman. frequent face-to-face discussions them clearly motivating factor decision take such challenging project. To enhance observable, chose heavy nuclei which gamma transitions strongly hindered. Eventually, observed 1972 percent decay spin-8, odd-parity isomer hafnium-180, world record.Even more attempt time-reversal still hypothetical. Although what seemingly iridium-191, interaction photon atomic electrons causes phase shift resembles caused nonconservation.After sabbatical CERN 1972, turned attention used muonic pionic atoms study it. started program recently established Los Alamos Meson Physics Facility (now Neutron Science Center). While there, performed, work, tests Klein–Gordon equation using pions.In 1980s initiated number groundbreaking neutrino paved way many contemporary activities discoveries field. working oscillations reactors sources: first baseline tens meters Institut Laue–Langevin research reactor France, collaboration friend colleague Rudolf Mössbauer, then Gösgen power plant Their careful measurements did not reveal oscillations, contradiction hints experiments.After early indications atmospheric 2000 helped build kilometer-baseline experiment Palo Verde Nuclear Generating Station Arizona. One kilometer indeed correct discovery, but colleagues missed it because experiment’s insufficient sensitivity mixing parameter.Oscillations finally discovered collaborations included alumni Verde: KamLAND Japan 100 km Daya Bay Reactor Neutrino Experiment China, same 1 substantially better small mixing. ways, confidence vindicated.Continuing area neutrinos, developed double experiments. simple germanium detector built pioneering time-projection chamber filled 5 kg isotopically enriched xenon. some extent, liquid-phase EXO 200 future ton nEXO follow work.In 1995 Tom W. Bonner Prize American Physical Society. had engagement Aspen Center Physics, served trustee 1976 1979. Over years mentored went have successful careers worldwide.Felix creative fearless charting directions uncompromising interpreting data. sense humor cultural interests beyond inspiration colleagues. deeply missed.© 2021 Institute Physics.