Liquid helium of liquid water. Helium was first liquefied on July 10, 1908, by the Dutch physicist Heike Kamerlingh Onnes at the University of Leiden in the Netherlands. At that time, helium-3 was unknown because the mass spectrometer had not yet been invented. In more recent decades, liquid helium has been used as a cryogenic refrigerant, and liquid helium is produced commercially for use in superconducting magnets such as those used in magnetic resonance imaging (MRI), nuclear magnetic resonance (NMR), Magnetoencephalography (MEG), and experiments in physics, such as low temperature Mössbauer spectroscopy. The temperature required to produce liquid helium is low because
Frans Michel Penning Derksen in 1921 and they had four children named Lourens, Hendricus, Paul, and Nellie. In 1924, Penning was hired as an experimental physicist at the Dutch section of the Phillips research department located in the Strijp district of Eindhoven. Gilles Holst, former assistant to Heike Kamerlingh Onnes, and head of the Philips Natuurkundig Laboratorium (NatLab), tasked Penning with continuing research on gas discharge phenomena to develop new lamps. Penning investigated breakdown energy potentials of low pressure inert gas discharges. In 1926, Penning observed that electrons under direct voltage current in low-pressure mercury discharges reach high velocities due to high-frequency oscillations