WebAlthough there are nine known isotopes of helium (2 He) (standard atomic weight: 4.002 602 (2)), only helium-3 (3 He) and helium-4 (4 He) are stable. All radioisotopes are short-lived, the longest-lived being 6 He with a half-life of 806.92(24) milliseconds.The least stable is 10 He, with a half-life of 260(40) yoctoseconds (2.6(4) × 10 −22 s), although it is …

WebDetection technique. Helium is used as a tracer because it penetrates small leaks rapidly. Helium also has the properties of being non-toxic, chemically inert and present in the atmosphere only in minute quantities (5 ppm).Typically a helium leak detector will be used to measure leaks in the range of 10 −5 to 10 −12 Pa·m 3 ·s −1.. A flow of 10 −5 Pa·m 3 ·s …

WebLiquid helium is a physical state of helium at very low temperatures at standard atmospheric pressures.Liquid helium may show superfluidity.. At standard pressure, the chemical element helium exists in a liquid form only at the extremely low temperature of −269 °C (−452.20 °F; 4.15 K). Its boiling point and critical point depend on which isotope …

Webtable Général Symbole 3 2 He 1 Neutrons 1 Protons 2 Données physiques Présence naturelle 0,000134(3) % Demi-vie Stable Masse atomique 3,01602932197(6) u Spin 1/2+ Excès d'énergie 14 931,218 88 ± 0,000 06 keV Énergie de liaison par nucléon 2 573 ± 0 keV modifier L’ hélium 3 , noté 3 He , est l' isotope de l' hélium dont le nombre de masse est …

WebA lifting gas or lighter-than-air gas is a gas that has a density lower than normal atmospheric gases and rises above them as a result. It is required for aerostats to create buoyancy, particularly in lighter-than-air aircraft, which include free balloons, moored balloons, and airships.Only certain lighter than air gases are suitable as lifting gases. Dry …

WebA helium–neon laser or He-Ne laser, is a type of gas laser whose high energetic medium gain medium consists of a mixture of 10:1 ratio of helium and neon at a total pressure of about 1 torr inside of a small electrical discharge.The best-known and most widely used He-Ne laser operates at a wavelength of 632.8 nm, in the red part of the visible spectrum.

WebHelium accumulates in the cores of stars as a result of the proton–proton chain reaction and the carbon–nitrogen–oxygen cycle.. Nuclear fusion reaction of two helium-4 nuclei produces beryllium-8, which is highly unstable, and decays back into smaller nuclei with a half-life of 8.19 × 10 −17 s, unless within that time a third alpha particle fuses with the beryllium-8 …

WebHelium-4 (4 He) is a stable isotope of the element helium.It is by far the more abundant of the two naturally occurring isotopes of helium, making up about 99.99986% of the helium on Earth. Its nucleus is identical to an alpha particle, and consists of two protons and two neutrons.. Alpha decay of heavy elements in the Earth's crust is the source of most …

WebThe proton–proton chain is more prominent in stars the mass of the Sun or less. This difference stems from temperature dependency differences between the two reactions; pp-chain reaction starts at temperatures around 4 × 10 6 K (4 megakelvin), making it the dominant energy source in smaller stars. A self-maintaining CNO chain starts at …

WebGay-Lussac's law usually refers to Joseph-Louis Gay-Lussac's law of combining volumes of gases, discovered in 1808 and published in 1809. It sometimes refers to the proportionality of the volume of a gas to its absolute temperature at constant pressure. This law was published by Gay-Lussac in 1802, and in the article in which he described his …