Elements Talk — Helium

Helium, atomic number 2, is tHe second most abundant element in the universe. The most common isotopes ofhelium are 4He and 3He. The vast majority of helium is 4He, which has two protons and two neutrons. 3He has two protons and one neutron.

Gaseous helium is colorless and odorless. It is the simplest inert gas and is very stable. Because helium is difficult to react with other elements, it can be used as a protective gas to allow certain specific materials to only come into contact with helium. For example, in welding, helium can protect metals from oxidation at high temperatures. In industries related to vacuum sealing, helium can be used for vacuum leak detection: the mass of helium ions is small and easy to detect, and the content of helium in the air is very small, so it is not easily disturbed by the external environment during leak detection. In life, most nuclear magnetic resonance imaging equipment in hospitals uses liquid helium to maintain the low temperature environment required for superconducting magnets. Because the density of helium is less than that of air, children can also play with helium balloons. About 30% of the helium in the United States is used for medical treatment in the form of liquid helium, 30% of the helium is used for space projects and defense, 10% of the helium is used for semiconductor processes, and 10% of the helium is used for scientific research (most of which is also in liquid form) and balloons.

Although there is a lot of helium in the universe, there is not much helium on Earth. 78% of the atmosphere is nitrogen, 21% is oxygen, but only 5 parts per million is helium. The cost of obtaining helium from the air is too high, and helium is generally obtained through some helium-rich natural gas. Helium is considered a non-renewable resource. Countries rich in helium include the United States, Qatar, Algeria and Russia. The helium in these natural gases may come from the natural nuclear reaction of uranium and thorium in rocks, and is "confined" underground by some special rocks. Unlike most gases, helium has very strong penetrability and can penetrate most rocks and even metals at room temperature. Because the speed at which helium penetrates metal is much lower than the speed of "leakage" that people usually define, helium can still be used as an identifying gas for vacuum leak detection. It is worth mentioning that there is no absolutely leak-proof vacuum equipment. The so-called water-tight, gas-tight and leak-tight all correspond to certain leak rate standards (the unit is air pressure × volume/time), and the leak rate can be lower than a certain value. At room temperature, fiberglass can better prevent helium from penetrating.