The symbol for helium is He.
The element helium is the second most abundant element in the universe after hydrogen, accounting for about 24% of the mass of galactic bodies. Astronomers Pierre Jules cesar Janssen and Joseph Norman Lockyer discovered it in 1868 when they observed an unknown characteristic spectral line in sunlight.
But it wasn't until 1895 that British chemist Sir William Ramsay discovered that helium was also found on Earth in a uranium-rich radioactive vein, and in 1903 large quantities of helium were found in natural gas fields in the U.S.
Uses:
1. Cryogenic Cooling: Utilizing liquid helium's low boiling point of -268.9°C, liquid helium can be used for ultra-low temperature cooling. And the ultra-low temperature cooling technology has a wide range of applications in fields such as superconducting technology. Superconducting materials need to be at low temperatures (around 100K) in order to exhibit superconducting properties, and in most cases only liquid helium can realize such extremely low temperatures relatively easily. Superconducting technology has large applications in the transportation industry for magnetic levitation trains and in the medical field for nuclear magnetic **** vibration imaging equipment.
2, balloon inflation: because helium density is much smaller than air (air density of 1.29kg / cubic meter, helium density of 0.1786kg / cubic meter), and the chemical nature of the extremely inactive, safer than hydrogen (hydrogen can be burned in the air may cause an explosion), helium is commonly used in airships or advertising balloons in the filling of the gas.
3, inspection and analysis: instrumental analysis of commonly used nuclear magnetic **** vibration analyzer superconducting magnets need to use liquid helium cooling, gas chromatography analysis of helium is often used as a carrier gas, the use of helium permeability is good, non-combustible characteristics of helium, helium is also used in vacuum leak detection, such as helium mass spectrometry leak detector.
4, protective gas: the use of helium inactive chemical properties, helium is commonly used in magnesium, zirconium, aluminum, titanium and other metal welding protective gas.
5, other aspects: helium can be used as a high-vacuum devices, atomic nuclear reactors in rockets, spacecraft used to transport liquid hydrogen, liquid oxygen and other liquid propellants pressurized gas. Helium is also used as a cleaning agent for atomic reactors, in the field of marine development in the breathing gas mixture, gas thermometer filling gas, etc..
Reference for the above: Baidu Encyclopedia-Helium