Helium is an important source of low temperatures. At the temperature of liquid helium, the thermal motion of atoms and free electrons in solids is practically absent, which allows for the study of many new phenomena, such as superconductivity in the solid state. Gaseous helium is used as a lightweight gas for filling air balloons. Since it is non-flammable, it is added to hydrogen for filling the envelope of a dirigible. Because helium is less soluble in blood than nitrogen, large quantities of helium are used in breathing mixtures for pressure-related work, such as deep-sea diving, underwater tunnel construction, and facilities. The use of helium in decompression (removal of dissolved gas from the blood) in divers is less painful, reduces the risk of decompression sickness, and eliminates phenomena such as nitrogen narcosis, which is a constant and dangerous companion to a diver’s work. Helium-oxygen (He-O2) mixtures are used, due to their low viscosity, for relieving asthma attacks and treating various respiratory tract disorders.
Helium is used as an inert shielding gas for arc welding, especially for magnesium and its alloys, in the production of silicon, germanium, titanium, and zirconium, and for cooling nuclear reactors. Other applications of helium include gas purging of bearings, neutron detectors (helium-3), gas thermometers, X-ray spectroscopy, food preservation, and high-voltage switches. When mixed with other noble gases, helium is used in external neon advertising (in gas discharge tubes). Liquid helium is advantageous for cooling superconducting magnets, particle accelerators, and other devices. An unusual application of helium as a refrigerant is the continuous mixing of 3He and 4He to create and maintain temperatures below 0.005 K.
Historical Background
Helium was first identified as a chemical element in 1868 by P. Janssen during the study of solar eclipses in India. A bright yellow line was observed in the spectral analysis of the solar chromosphere, initially attributed to the spectrum of sodium. However, in 1871, J. Lockyer and P. Janssen proved that this line did not belong to any known elements on Earth. Lockyer and E. Frankland named this new element “helium” from the Greek word , meaning the sun. At that time, it was not known that helium was an inert gas, and it was believed to be a metal. It was only almost a quarter century later that helium was discovered on Earth. In 1895, shortly after the discovery of argon, W. Ramsay and Swedish chemists P. Cleve and N. Langlet independently established that helium is released when heating the mineral cleveite. A year later, G. Cailletet discovered traces of helium in the atmosphere, and in 1906, helium was found in natural gas wells in Kansas. In the same year, E. Rutherford and T. Royds determined that alpha particles emitted by radioactive elements were helium nuclei.
