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Noble gases have very low boiling and melting points, which makes them useful as cryogenicrefrigerants.[1] In particular, liquid helium, which boils at 4.2 K (−268.95 °C; −452.11 °F), is used for superconducting magnets, such as those needed in nuclear magnetic resonance imaging and nuclear magnetic resonance.[2] Liquid neon, although it does not reach temperatures as low as liquid helium, also finds use in cryogenics because it has over 40 times more refrigerating capacity than liquid helium and over three times more than liquid hydrogen.[3]
Helium is used as a component of breathing gases to replace nitrogen, due its low solubility in fluids, especially in lipids. Gases are absorbed by the blood and body tissues when under pressure like in scuba diving, which causes an anesthetic effect known as nitrogen narcosis.[4] Due to its reduced solubility, little helium is taken into cell membranes, and when helium is used to replace part of the breathing mixtures, such as in trimix or heliox, a decrease in the narcotic effect of the gas at depth is obtained.[5] Helium's reduced solubility offers further advantages for the condition known as decompression sickness, or the bends.[6][7] The reduced amount of dissolved gas in the body means that fewer gas bubbles form during the decrease in pressure of the ascent. Another noble gas, argon, is considered the best option for use as a drysuit inflation gas for scuba diving.[8] Helium is also used as filling gas in nuclear fuel rods for nuclear reactors.[9]
Noble gases are commonly used in lighting because of their lack of chemical reactivity. Argon, mixed with nitrogen, is used as a filler gas for incandescent light bulbs.[3] Krypton is used in high-performance light bulbs, which have higher color temperatures and greater efficiency, because it reduces the rate of evaporation of the filament more than argon; halogen lamps, in particular, use krypton mixed with small amounts of compounds of iodine or bromine.[3] The noble gases glow in distinctive colors when used inside gas-discharge lamps, such as "neon lights". These lights are called after neon but often contain other gases and phosphors, which add various hues to the orange-red color of neon. Xenon is commonly used in xenon arc lamps, which, due to their nearly continuous spectrum that resembles daylight, find application in film projectors and as automobile headlamps.[3]
The noble gases are used in excimer lasers, which are based on short-lived electronically excited molecules known as excimers. The excimers used for lasers may be noble gas dimers such as Ar2, Kr2 or Xe2, or more commonly, the noble gas is combined with a halogen in excimers such as ArF, KrF, XeF, or XeCl. These lasers produce ultraviolet light, which, due to its short wavelength (193 nm for ArF and 248 nm for KrF), allows for high-precision imaging. Excimer lasers have many industrial, medical, and scientific applications. They are used for microlithography and microfabrication, which are essential for integrated circuit manufacture, and for laser surgery, including laser angioplasty and eye surgery.[12]
Some noble gases have direct application in medicine. Helium is sometimes used to improve the ease of breathing of people with asthma.[3] Xenon is used as an anesthetic because of its high solubility in lipids, which makes it more potent than the usual nitrous oxide, and because it is readily eliminated from the body, resulting in faster recovery.[13] Xenon finds application in medical imaging of the lungs through hyperpolarized MRI.[14] Radon, which is highly radioactive and is only available in minute amounts, is used in radiotherapy.[6]
Noble gases, particularly xenon, are predominantly used in ion engines due to their inertness. Since ion engines are not driven by chemical reactions, chemically inert fuels are desired to prevent unwanted reaction between the fuel and anything else on the engine.
Oganesson is too unstable to work with and has no known application other than research.
In many applications, the noble gases are used to provide an inert atmosphere. Argon is used in the synthesis of air-sensitive compounds that are sensitive to nitrogen. Solid argon is also used for the study of very unstable compounds, such as reactive intermediates, by trapping them in an inert matrix at very low temperatures.[15] Helium is used as the carrier medium in gas chromatography, as a filler gas for thermometers, and in devices for measuring radiation, such as the Geiger counter and the bubble chamber.[16] Helium and argon are both commonly used to shield welding arcs and the surrounding base metal from the atmosphere during welding and cutting, as well as in other metallurgical processes and in the production of silicon for the semiconductor industry.[3]
The relative isotopic abundances of noble gases serve as an important geochemical tracing tool in earth science[17]. They can unravel the Earth's degassing history and its effects to the surrounding environment (i.e., atmosphere composition[18]). Due to their inert nature and low abundances, change in the noble gas concentration and their isotopic ratios can be used to resolve and quantify the processes influencing their current signatures across geological settings [17][19].
Helium has two abundant isotopes: helium-3, which is primordial with high abundance in earth's core and mantle, and helium-4, which originates from decay of radionuclides (232Th, 235,238U) abundant in the earth's crust. Isotopic ratios of helium are represented by RA value, a value relative to air measurement (3He/4He = 1.39*10-6)[20]. Volatiles that originate from the earth's crust have a 0.02-0.05 RA, which indicate an enrichment of helium-4[21]. Volatiles that originate from deeper sources such as subcontinental lithospheric mantle (SCLM), have a 6.1± 0.9 RA[22] and mid-oceanic ridge basalts (MORB) display higher values (8 ± 1 RA). Mantle plume samples have even higher values than > 8 RA[22][23] . Solar wind, which represent an unmodified primordial signature is reported to have ~ 330 RA[24].
Neon has three main stable isotopes:20Ne, 21Ne and 22Ne, with 20Ne produced by cosmic nucleogenic reactions, causing high abundance in the atmosphere[19][25]. 21Ne and 22Ne are produced in the earth's crust as a result of interactions between alpha and neutron particles with light elements; 18O, 19F and 24,25Mg[26]. The neon ratios (20Ne/22Ne and 21Ne/22Ne) are systematically used to discern the heterogeneity in the Earth's mantle and volatile sources. Complimenting He isotope data, neon isotope data additionally provide insight to thermal evolution of Earth's systems[27].
Argon has three stable isotopes: 36Ar, 38Ar and 40Ar. 36Ar and 38Ar are primordial, with their inventory on the earth's crust dependent on the equilibration of meteoric water with the crustal fluids[19]. This explains huge inventory of 36Ar in the atmosphere. Production of these two isotopes (36Ar and 38Ar) is negligible within the earth's crust, only limited concentrations of 38Ar can be produced by interaction between alpha particles from decay of 235,238U and 232Th and light elements (37Cl and 41K). While 36Ar is continuously being produced by Beta-decay of 36Cl[32][33]. 40Ar is a product of radiogenic decay of 40K. Different endmembers values for 40Ar/36Ar have been reported; Air = 295.5[34], MORB = 40,000[34], and crust = 3000[19].
Krypton has several isotopes, with 78, 80, 82Kr being primordial, while 83,84, 86Kr results from spontaneous fission of 244Pu and radiogenic decay of 238U [35][19]. Krypton's isotopes geochemical signature in mantle reservoirs resembling the modern atmosphere. preserves the solar-like primordial signature[36]. Krypton isotopes have been used to decipher the mechanism of volatiles delivery to earth's system, which had great implication to evolution of earth (nitrogen, oxygen, and oxygen) and emergence of life[37]. This is largely due to a clear distinction of krypton isotope signature from various sources such as chondritic material, solar wind and cometary[38][39].
Xenon has nine isotopes, most of which are produced by the radiogenic decay. Krypton and xenon noble gases requires pristine, robust geochemical sampling protocol to avoid atmospheric contamination[40]. Furthermore, sophisticated instrumentation is required to resolve mass peaks among many isotopes with narrow mass difference during analysis.
Noble gas measurements can be obtained from sources like volcanic vents, springs, and geothermal wells following specific sampling protocols[44].The classic specific sampling protocol include the following.
A field setup for collecting gas sample intended for noble gas analysis. The sampling setup includes the inverted funnel on top of the hot spring with macro seep, two copper tubes connected with TygonⓇ tube.Copper tubes - These are standard refrigeration copper tubes, cut to ~10 cm³ with a 3/8” outer diameter, and are used for sampling volatile discharges by connecting an inverted funnel to the tube via TygonⓇ tubing, ensuring one-way inflow and preventing air contamination. Their malleability allows for cold welding or pinching off to seal the ends after sufficient flushing with the sample.
Sampling of noble gases using a Giggenbach bottle, a funnel is placed on top of the hot spring to focus the stream of sample towards the bottle via the Tygon tube. A geochemist is controlling the flow of the sample inlet using a Teflon valve. Note the condensation process inside the evacuated Giggenbach bottle.Giggenbach bottles - Giggenbach bottles are evacuated glass flasks with a Teflon stopcock, used for sampling and storing gases. They require pre-evacuation before sampling, as noble gases accumulate in the headspace [45]. These bottles were first invented and distributed by a Werner F. Giggenbach, a German chemist[46].
TedlarⓇ bags/ Multi-layered foil bags - These are cost effective bags, that also requires pre-evacuation before sampling, they are easily adaptable to instruments analysis lines[47].
Noble gases have numerous isotopes and subtle mass variation that requires high-precision detection systems. Originally, scientists used magnetic sector mass spectrometry, which is time-consuming and has low sensitivity due to "peak jumping mode"[48][49]. Multiple-collector mass spectrometers, like Quadrupole mass spectrometers (QMS), enable simultaneous detection of isotopes, improving sensitivity and throughput[49]. Before analysis, sample preparation is essential due to the low abundance of noble gases, involving extraction, purification system[17]. Extraction allows liberation of noble gases from their carrier (major phase; fluid or solid) while purification remove impurities and improve concentration per unit sample volume[50]. Cryogenic traps are used for sequential analysis without peak interference by stepwise temperature raise[51].
Research labs have successfully developed miniaturized field-based mass spectrometers, such as the portable mass spectrometer (miniRuedi), which can analyze noble gases with an analytical uncertainty of 1-3% using low-cost vacuum systems and quadrupole mass analyzers[52].
Extraction and purification (clean up) mass spectrometer line.A typical quadrupole mass analyzer mode of function that is used in lab-based mass spectrometer and field-based mass spectrometer.
^Maiken, Eric (1 August 2004). "Why Argon?". Decompression. Retrieved 26 June 2008.
^Horhoianu, G.; Ionescu, D. V.; Olteanu, G. (1999). "Thermal behaviour of CANDU type fuel rods during steady state and transient operating conditions". Annals of Nuclear Energy. 26 (16): 1437–1445. doi:10.1016/S0306-4549(99)00022-5.
^"Disaster Ascribed to Gas by Experts". The New York Times. 7 May 1937. p. 1.
^Dunkin, I. R. (1980). "The matrix isolation technique and its application to organic chemistry". Chem. Soc. Rev. 9: 1–23. doi:10.1039/CS9800900001.
^Hwang, Shuen-Chen; Lein, Robert D.; Morgan, Daniel A. (2005). "Noble Gases". Kirk Othmer Encyclopedia of Chemical Technology. Wiley. pp. 343–383. doi:10.1002/0471238961.0701190508230114.a01.
