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Topic: Liquid Helium

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	Helium - MSN Encarta
		Helium is used to pressurize and stiffen the structure of rockets before take-off and to pressurize the tanks of liquid hydrogen or other fuel in order to force fuel into the rocket engines.
		Helium is used in inert-gas arc welding for light metals such as aluminium and magnesium alloys that might otherwise oxidize; the helium protects heated parts from attack by air.
		Helium is used in place of nitrogen as part of the synthetic atmosphere breathed by deep-sea divers, caisson workers, and others, because it reduces susceptibility to the bends.
	uk.encarta.msn.com /encyclopedia_761562418/Helium.html (731 words)

	helium. The Columbia Encyclopedia, Sixth Edition. 2001-05
		Helium was isolated (1895) from a sample of the uranium mineral cleveite by Sir William Ramsay.
		Some helium is extracted directly from the atmosphere; the gas is also found in certain uranium minerals and in some mineral waters, but not in economic quantities.
		Liquid helium is essential for many low temperature applications (see low-temperature physics).
	www.bartleby.com /65/he/helium.html (570 words)

	Helium - Wikipedia, the free encyclopedia
		Helium gas is used to fill the space between lenses in some solar telescopes because its extremely low index of refraction reduces the distorting effect of temperature variations in the gas filling the telescope (some telescopes are filled with vacuum instead).
		Helium was first detected on August 18, 1868 as a bright yellow line with a wavelength of 587.49 nm in the spectrum of the chromosphere of the Sun, by French astronomer Pierre Janssen during a total solar eclipse in India.
		Helium is the second most abundant element in the known Universe after hydrogen and constitutes 23% of all elemental matter measured by mass even though there are 8 times as many hydrogen atoms as helium ('elemental matter' does not include dark matter or dark energy, which together may account for 96% of the Universe).
	en.wikipedia.org /wiki/Helium (4912 words)

	Liquid helium - Wikipedia, the free encyclopedia
		Liquid helium-4 is commercially important today because of its use as a cryogenic refrigerants for conventional superconducting magnets such as those used in MRI, NMR, quantum dots, and amorphous solid waters.
		The temperatures required to liquify helium are low because of the weakness of the attraction between helium atoms.
		The zero point energy of the liquid is less if the atoms are less confined by their neighbors; thus the liquid can lower its ground state energy by increasing the interatomic distance.
	en.wikipedia.org /wiki/Liquid_helium (342 words)

	Liquid Helium
		Liquid helium is inert, colorless, odorless, non-corrosive, extremely cold, and nonflammable.
		Helium is typically withdrawn as a liquid but may be withdrawn as a gas at low flow rates and pressure.
		To transfer liquid helium, a vacuum jacketed withdrawal stinger (dip tube) is first inserted through V-1 (white); V-3 (green) is closed and V-2 (yellow) is opened and used to pressurize the liquid container with clean dry helium gas.
	www-safety.deas.harvard.edu /services/helium.html (1162 words)

	Encyclopedia: Helium (Site not responding. Last check: 2007-10-22)
		Helium Dating (or He dating) is the method of age determination that depends on the production of helium during the decay of the radioactive isotopes uranium-235(U-235), uranium-238(U-238), and thorium-232(Th-232).
		In rocketry helium is used as an ullage medium to displace fuel and oxidizers in storage tanks and to condense hydrogen and oxygen to make rocket fuel.
		Helium produced before 1945 was about 98% pure (2% nitrogen), which was adequate for airships.
	www.nationmaster.com /encyclopedia/Helium (10823 words)

	Helium (Site not responding. Last check: 2007-10-22)
		Helium has the lowest melting point of any element and has found wide use in cryogenic research as its boiling point is close to absolute zero.
		Containers filled with helium gas at 5 to 10 K should be treated as though they contained liquid helium due to the large increase in pressure resulting from warming the gas to room temperature.
		Helium is widely used as an inert gas shield for arc welding; as a protective gas in growing silicon and germanium crystals, and in titanium and zirconium production; as a cooling medium for nuclear reactors, and as a gas for supersonic wind tunnels.
	www.scescape.net /~woods/elements/helium.html (798 words)

	Helium
		Helium is used to pressurize and stiffen the structure of rockets before takeoff and to pressurize the tanks of liquid hydrogen or other fuel in order to force fuel into the rocket engines.
		Helium is used in inert-gas arc welding for light metals such as aluminum and magnesium alloys that might otherwise oxidize; the helium protects heated parts from attack by air.
		Helium, which may be essential to future advanced technologies, was not stockpiled by the U.S. government between 1973 and 1980, nor were private natural-gas producers required to recover helium from their wells.
	www.jepsenmaintenance.com /helium.htm (880 words)

	CRYOFAB - Cryogenics for Industry, Research, Laboratory, Medical and Homecare.
		Liquid helium is a colorless, nontoxic liquid with a density of one-eighth that of water, inert under all temperature and pressure conditions.
		The height of the liquid observed may be converted to a volumetric equivalent by using the calibration chart attached to the dewar.
		Liquid transfer will begin as soon as the transfer line cools down if there is sufficient pressure in the dewar (2-4 psig).
	www.cryofab.com /html/manual_14.htm (1578 words)

	helium
		Helium was discovered in the gaseous atmosphere surrounding the Sun by the French astronomer Pierre Janssen, who detected a bright yellow line in the spectrum of the solar chromosphere during an eclipse in 1868; this line was initially assumed to represent the element sodium.
		Helium constitutes about 23 percent of the mass of the universe and is thus second in abundance to hydrogen in the cosmos.
		This liquid form is called helium II to distinguish it from normal liquid helium I. By contrast, the less plentiful helium-3 forms three distinguishable liquid phases (see Figure B), of which two are superfluids.
	www.britannica.com /nobel/micro/713_23.html (617 words)

	Helium (Site not responding. Last check: 2007-10-22)
		Helium has the lowest melting point of any element and has found wide use in cryogenic research, as its boiling point is close to absolute zero.
		Using liquid helium, Kurti and co-workers, and others, have succeeded in obtaining temperatures of a few microkelvins by the adiabatic demagnetization of copper nuclei, starting from about 0.01 K. Seven isotopes of helium are known.
		Helium is widely used as an inert gas shield for arc welding; as a protective gas in growing silicon and germanium crystals, and in titanium and zirconium production; as a cooling medium for nuclear reactors, and as a gas for supersonic wind tunnels.
	www.sunysccc.edu /academic/mst/ptable/he.html (835 words)

	Tech Air - Cryogenic Liquids - Liguid Helium
		Liquid helium-4 is used as a cryogenic refrigerant; it is produced commercially for use in superconducting magnets such as those used in MRI or NMR.
		The temperatures required to liquify helium are low because of the weakness of the attraction between helium atoms.
		The zero point energy of the liquid is less if the atoms are less confined by their neighbors; thus the liquid can lower its ground state energy by increasing the interatomic distance.
	www.techair.com /medical_scientific/cryoliquids2.html (319 words)

	2G Enterprises - Cryo-Manual - 2. Liquid Helium Refills
		The most crucial operation with the SRM DEWAR is the refilling of the reservoir with liquid helium.
		As soon as liquid helium from the SUPPLY dewar starts to enter the SRM dewar reservoir it will abruptly cool the gas in the reservoir and in some cases can produce a pressure in the reservoir lower than ambient.
		Liquid should collect at a rate of 3 liters per minute or roughly 5% per minute on the level gauge.
	www.2genterprises.com /cryo_manual_2.html (2713 words)

	Liquid helium -- Facts, Info, and Encyclopedia article (Site not responding. Last check: 2007-10-22)
		The temperatures required to liquify helium are low because of the weakness of the attraction between helium ((physics and chemistry) the smallest component of an element having the chemical properties of the element) atoms.
		The (Click link for more info and facts about zero point energy) zero point energy of the liquid is less if the atoms are less confined by their neighbors; thus the liquid can lower its ((physics) the lowest energy state of an atom or other particle) ground state energy by increasing the interatomic distance.
		Liquid helium-3 and helium-4 are not completely miscible below 0.9 K at the saturated (The pressure exerted by a vapor; often understood to mean saturated vapor pressure (the vapor pressure of a vapor in contact with its liquid form)) vapor pressure.
	www.absoluteastronomy.com /encyclopedia/l/li/liquid_helium.htm (505 words)

	Physics Today On The Web - Cover Story
		Helium remains a liquid at absolute zero because the interatomic forces are extremely weak and the small helium mass results in a large zero-point energy.
		The inertia of the liquid surrounding the bubble causes the radius of the cavity to increase beyond the radius corresponding to the minimum energy configuration.
		In the experiment, 0.6 K was the measured temperature of the liquid before the pressure was reduced; during the expansion of the liquid that took place before cavitation, however, the temperature should decrease by about a factor of three.
	www.aip.org /pt/feb00/maris.htm (4210 words)

	It's Elemental - The Element Helium
		Helium, the second most abundant element in the universe, was discovered on the sun before it was found on the earth.
		Helium is combined with oxygen to create a nitrogen free atmosphere for deep sea divers so that they will not suffer from a condition known as nitrogen narcosis.
		Liquid helium is an important cryogenic material and is used to study superconductivity and to create superconductive magnets.
	education.jlab.org /itselemental/ele002.html (420 words)

	[No title] (Site not responding. Last check: 2007-10-22)
		Subtract the measurements to obtain the depth of the liquid helium chamber.
		EPR Analysis of Cells-- K562 cells were stored in liquid nitrogen and analyzed using a high quality spherical resonator (SP9703) on a Bruker EMX EPR spectrometer with an Oxford Instruments liquid helium cryostat.
		Containers filled with helium gas at 5 to 10 K should be treated as though they contained liquid helium due to the large increase in pressure resulting from warming the gas to room temperature.
	www.lycos.com /info/helium-element--liquid.html (481 words)

	Helium
		By contrast, the critical temperature of helium is 5.2K, the critical pressure is 2.26 atm, and the critical density is 0.0693 g/cc.
		Helium II is actually a many-particle system in which some of the atoms are in the superfluid ground state, while the remainder are in excited states, whose energies are functions of their momenta.
		Helium and argon are used in welding to shield the hot metal from the atmosphere, especially in the case of reactive metals.
	www.du.edu /~jcalvert/phys/helium.htm (8914 words)

	Nucleation of Bubbles in Liquid Helium
		Helium is the simplest and most understandable material, and the fundamental properties of liquid helium has been studied very well over wide temperature and pressure ranges.
		But helium has so many unique characters that helium is still one of the materials which is still being studied a lot all over the world.
		And because liquid helium stays liquid state under its own vapor pressure even the temperature is as close to absolute zero as possible, quantum phenomena can be observed macroscopically.
	www.geocities.com /ResearchTriangle/Thinktank/9869/Lab/LabWork.html (377 words)

	Helium
		Helium is tasteless, odorless, colorless, normally nontoxic, and the second most abundant element in existence.
		Helium is not very dense, so it's easier for the larynx to vibrate surrounded by helium than by air.
		Present helium consumption is estimated to be about 100 million cubic metres, and is predicted to continue rising by 4 to 5 percent a year.
	www.chemmybear.com /helium.html (1137 words)

	Liquid helium, superfluidity
		When helium is cooled to a critical temperature of 2.17 K (called its lambda point), a remarkable discontinuity in heat capacity occurs, the liquid density drops, and a fraction of the liquid becomes a zero viscosity "superfluid".
		An important application of liquid helium has been in the study of superconductivity and for the applications of superconducting magnets.
		When helium is cooled to a critical temperature of 2.17 K, a remarkable discontinuity in heat capacity occurs, the liquid density drops, and a fraction of the liquid becomes a zero viscosity "superfluid".
	hyperphysics.phy-astr.gsu.edu /hbase/lhel.html (386 words)

	Liquid Helium Storage Dewars, Pulsation Dipstick - Janis Research
		The Stratos® 100 SL liquid helium dewar is a type-approved transport vessel (according to ADR/RID) for transport in closed condition under pressure with:
		This simple liquid helium probe provides an accurate indication of the liquid level in a storage dewar or research cryostat.
		The dipstick produces a steady low frequency pulsation when immersed in liquid helium which can easily be seen on the gauge or felt at the diaphragm with a finger tip.
	www.janis.com /p-aae3.html (278 words)

	Helium
		Helium is used for making things rise or stay in the air.
		Helium is what they call a "Noble Gas." This is because all the electrons are present in the valence level of the atom.
		Helium is a colorless and odorless gas at room temperature.
	www.mvschools.org /ms/projects/html/black/helium.htm (391 words)

	LHe_Fill
		Slowly insert the flutter (thumper) tube into the liquid helium fill port until it touches the bottom of the can, then place an alligator clip on the tube, which is level with the top of the fill port.
		The amount of liquid helium in the container is not the volume of the container but the amount that is accessible to transfer with a stinger.
		The collapsing exhaust indicates that the liquid helium is reaching the magnet end of the transfer tube and is filling the magnet.
	www.chemistry.nmsu.edu /Instrumentation/LHe_Fill.html (2594 words)

	Physics at Minnesota: Liquid Helium Production (Site not responding. Last check: 2007-10-22)
		Helium orders will be dropped off next to room 15 in Tate Laboratory of Physics.
		The price for liquid helium will be $3.25/liquid liter, with a credit of $2.00/liquid-liter-equivalent of gas actually recovered.
		Helium should be ordered, with 24 hours advance notice via electronic mail at helium@physics.umn.edu.
	www.physics.umn.edu /resources/helium.html (307 words)

	LN2_LHe
		If the helium can runs dry before the magnet is completely de-energized, the magnet will probably quench and the superconductive coil could be damaged since there will be no liquid helium left to transfer some of the heat from the coil.
		A bouncing ball is an indicator of oscillation in the helium vessel.
		It is possible for the helium manifold pressure relief balls to become unseated during a liquid helium transfer or after a magnet quench.
	www.chemistry.nmsu.edu /Instrumentation/LN2_LHe.html (4866 words)

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