Liquid Helium Research Papers - Academia.edu (original) (raw)

Helium, chemical symbol He, atomic number 2, the second most abundant chemical element in the earth universe after hydrogen (H 76 percent; He 23 percent) is a colorless, orderless, and tasteless gas and liquid at-268 °C. The noble gases or group-18 element of the periodic table, helium formed in the thermonuclear reactions on stars but it present to a very negligible extent in the earth atmosphere due to the lightness of gas. The boiling and freezing point of helium is lower than any known chemical substances of the universe and cannot be solidified by sufficient cooling at normal atmospheric pressure. Helium gas consists of two stable isotopes with chemical formula He and He, He-4 is formed on earth by alpha particle decay of radioactive elements, but He-3 is formed by nuclear reactions induced by cosmic radiations. Prior to 1960 helium, neon, argon, krypton, xenon, and radon were belong to the family of inert or rare gases, now these are named noble gases. The noble gases were not known at Mendeleev's time. Today all the noble gases like helium, neon, argon, xenon, and radon are discovered and characterize and extreme inertness distinct from any other chemical elements of the periodic table. Helium atom (atomic number = 2 and mass number = 4) has two protons and neutrons in the nucleus and two extranuclear electrons surrounded the nucleus of the atom. 4 3