Helium

Discovered by : Pierre Jules César Janssen and Sir Joseph Norman Lockyer

Discovered in year : 1868

Helium is a colourless, odourless, tasteless, non-toxic, inert monatomic gas that heads the noble gas group in the periodic table. It's atomic number is 2 and has an atomic weight of 4.0026, which is represented by the symbol He. It is the second lightest element. Its boiling and melting  points are the lowest among the elements and it exists only as a gas except in extreme conditions. Next to hydrogen, it is the second most abundant element in universe, and accounts for 24% of the elemental mass of our galaxy. Helium which occurs today is the result of the natural radioactive decay of heavy radioactive elements (thorium and uranium), as the alpha particles that are emitted by such decays consist of helium-4 nuclei. This radiogenic helium is trapped with natural gas in concentrations up to seven percent by volume, from which it is extracted commercially by a low-temperature separation process called fractional distillation. Helium is found in abundance on Sun and Jupiter. This high abundance is due to the very high binding energy (per nucleon) of helium-4 with respect to the next three elements after helium (lithium, beryllium, and boron). This helium-4 binding energy also accounts for its commonality as a product in both nuclear fusion and radioactive decay. Most helium in the universe is helium-4, and was formed during the Big Bang. Mixtures of helium and oxygen are used as an artificial 'air' for divers and others working under pressure. Helium is used instead of the nitrogen in normal air because, after a long dive, helium leaves the body faster than nitrogen, allowing faster decompression.

History - It was on August 18, 1868 that the first evidence of helium was observed by French astronomer Pierre Janssen. He saw Helium as a bright yellow line with a wavelength of 587.49 nanometres in the spectrum of the chromosphere of the Sun. Pierre Janssen discovered it during a total solar eclipse in Guntur, India. This line was initially assumed to be sodium. On October 20 of the same year, English astronomer Norman Lockyer also observed a yellow line in the solar spectrum, which he named the D3 Fraunhofer line because it was near the known D1 and D2 lines of sodium. He concluded that it was caused by an element in the Sun unknown on Earth. Lockyer and English chemist Edward Frankland named the element with the Greek word 'Helios' which means the Sun God. Janssen is jointly credited with the discovery of the element with Norman Lockyer.

Development of the discovery of Helium

In 1882, Italian physicist Luigi Palmieri detected Helium on Earth, for the first time, through its D3 spectral line, when he analysed the lava of Mount Vesuvius.

On March 26, 1895 British chemist Sir William Ramsay isolated helium on Earth by treating the mineral cleveite (a variety of uraninite with at least 10% rare earth elements) with mineral acids.

In 1903, large reserves of helium were found in the natural gas fields of the United States, which is by far the largest supplier of the gas.

In 1907, Ernest Rutherford and Thomas Royds demonstrated that alpha particles are helium nuclei by allowing the particles to penetrate the thin glass wall of an evacuated tube, then creating a discharge in the tube to study the spectra of the new gas inside.

In 1908, helium was first liquefied by Dutch physicist Heike Kamerlingh Onnes by cooling the gas to less than one kelvin.

In 1938, Russian physicist Pyotr Leonidovich Kapitsa discovered that helium-4  has almost no viscosity at temperatures near absolute zero, a phenomenon now called super-fluidity.

Role of  Helium in the improvement of human life

• Helium became to be widely used in cryogenics. In fact cryogenics is its largest single use, accounting for about a quarter of production, mostly for the cooling of superconducting magnets, particularly the main commercial application in MRI  scanners.

• Helium also found it's usage in other industrial uses as a pressurizing and purge gas, and a protective atmosphere for arc welding and processes (such as growing crystals to make silicon wafers) which account for half of its use.

• In scientific research, the behaviour of liquid helium-4's two fluid phases, helium I and helium II, is important to researchers studying quantum mechanics especially the phenomenon of super-fluidity and to those looking at the effects that temperatures near absolute zero have on matter such as superconductivity.