Helium units

Table 8. Details of QED and higher-order relativistic contributions to the ionization energies of helium. Units axe MHz...

The most important source of helium is the natural gas from certain petroleum wells in the United States and Canada. This gas may contain as much as 8 % of helium. Because helium has a lower boiling point Table 12.1) than any other gas, it is readily obtained by cooling natural gas to a temperature at which all the other gases are liquid (77 K) almost pure helium can then be pumped off. The yearly production in this way may be many millions of m of gas. but something like 10 m per year is still wasted. 

The fusion of hydrogen into helium provides the energy of the hydrogen bomb. The helium content of the atmosphere is about 1 part in 200,000. While it is present in various radioactive minerals as a decay product, the bulk of the Free World s supply is obtained from wells in Texas, Oklahoma, and Kansas. The only known helium extraction plants, outside the United States, in 1984 were in Eastern Europe (Poland), the USSR, and a few in India. 

It has over 40 hmes more refrigerating capacity per unit volume than liquid helium and more than three hmes that of liquid hydrogen. It is compact, inert, and is less expensive than helium when it meets refrigeration requirements. 

A nucleus is composed of protons and neutrons, each of which has unit atomic mass. The number of protons characterizes each element. In going from one element to the next, the total number of protons increases by one. Thus the simplest element, hydrogen, has atoms having only one proton in the nucleus, and the next simplest, helium, has two protons in the nucleus. 

An atom of one of the simplest elements, helium, has a mass of 4 atomic units (Daltons) comprising 2 protons and 2 neutrons, whereas each atom of a heavier element, phosphorus, has 15 protons and 16 neutrons, giving it a mass of 31 Da. 

Brightness. This is defined as the power emitted per unit area of the output mirror per unit solid angle and is extremely high compared with that of a conventional source. The reason for this is that, although the power may be only modest, as in, for example, a 0.5 mW helium-neon gas laser, the solid angle over which it is distributed is very small. 

The principal source of helium is certain natural gas fields. The helium contents of more than 10,000 natural gases in various parts of the world have been measured (9). Helium concentrations of a few are Hsted in Table 2. In the United States, recovery of helium is economical only for helium-rich gases containing more than about 0.3 vol % belium. Most of the United States helium resources are located in the midcontinent and Rocky Mountain regions, and about 89% of the known United States supply is in the Hugoton field in Kansas, Oklahoma, and Texas the Keyes field in Oklahoma the Panhandle and Cliffside fields in Texas and the Riley Ridge area in Wyoming (11). 

Upon the United States entry into World War 1 in 1917, helium became a war material of first priority. Helium was sought to replace hydrogen as the lifting gas in lighter-than-air craft for military use. As a war material, helium became a government monopoly, was given a code name, and was shrouded in secrecy. By the war s end, quantities of helium had been produced, but none had reached combat. 

Helium from Natural Gas. Recovery of helium from a given natural-gas stream depends almost entirely on the total economic picture of the stream. In the United States, the lowest practical helium level that is recovered is most frequendy 0.3 vol %, although helium is frequendy ignored, and hence wasted, in streams containing somewhat high concentrations. In other parts of the wodd where political considerations sometimes interact with the economic, the use of helium concentrations lower than 0.3 vol % maybe dictated. 

Gaseous helium is commonly used as the working fluid ia closed-cycle cryogenic refrigerators because of chemical iaertness, nearly ideal behavior at all but the lowest temperatures, high heat capacity per unit mass, low viscosity, and high thermal conductivity. 

The most familiar gas laser is the helium—neon laser (23,24). Sales of commercial helium—neon lasers exceed 400,000 units per year. The helium—neon laser is a compact package that produces a continuous beam of orange-red light. The inside diameter of the tube is commonly around 1.5 mm. The output of helium—neon lasers available commercially ranges from a fraction of a milliwatt to more than 35 mW. They have many appHcations in the areas of alignment, supermarket scanning, educational demonstrations, and holography. 

Helium is extracted from natural gas in the southwestern United States and moved by a 685-km, 50-mm dia pipeline to storage in a partially depleted gas field near Amarillo, Texas, as part of the U.S. government s helium conservation program. 

Cmde helium (containing 50—70% helium, associated hydrogen and neon, 1—3% methane, and the balance nitrogen) can easily be obtained by minor enhancements to the nitrogen rejection unit, particularly with natural gases containing 0.5% or more helium. For example, by operating the double-column condenser in a partial condensation mode, a stream of uncondensed vapor at about 50% helium concentration can be obtained. This cmde helium stream can be fed directly to helium purification and Hquefaction units. 

Pressures Turboexpanders ean be designed to operate at up to 3,000 psi and higher inlet pressures as required by eonditions. Expansion pressure ratios ean also be adjusted for eaeh proeess over a wide range. A majority of effieient expansion ratios are below 5 1, although pressure ratios up to 10 1 ean be aeeommodated with reasonable effieieney. Smaller, lower pressure units are popular for air separation and helium liquefaetion. Intermediate pressure (100-1,000 psi) and high pressure expanders (1,000-3,000 psi) are widely used in natural gas proeessing and industrial gas liquefaetion. 

Gas emerges from each expander cooled to -61°C (-77°F). Additional heat exchangers lower the temperature to -84°C (-120°F), at which point all the LNG is removed for delivery. Residue gas, now under reduced pressure, is passed along to the nitrogen rejection unit (NRU) where inert nitrogen is separated and vented into the atmosphere. Helium is also recovered in the NRU. The remaining residue gas is 90% methane. 

When 5.00 mL of ether has been delivered by the syringe pump, the pump is shut off The reactor is allowed to run an additional 15 min before the fluorine and the mercury arcs ate shut off. The preaerosol furnace, the evaporator heater unit, and the coolant pump are shut off. Once the system approaches ambient conditions, all the helium carriers are shut off and the product trap valves are closed The product trap and its Dewar flask filled with liquid nitrogen are removed to the vacuum line where the trap is evacuated... 

Helium, the second element in the periodic table, has atomic number 2. This means its nucleus contains two protons and has a 2+ charge. The neutral atom, then, contains two electrons. There are two stable isotopes, helium-4 and helium-3, but the helium found in nature is almost pure helium-4. Helium is found in certain natural gas fields and is separated as a by-product. Sources of helium are rare and most of the world supply is produced in the United States, mainly in Texas and Kansas. 

Peptides inside the mass specttometet ate broken down into smaller units by coUisions with neuttal helium atoms (collision-induced dissociation), and the masses of the individual fragments are determined. Since peptide bonds are much more labile than carbon-carbon bonds, the most abundant fragments will differ from one another by units equivalent to one or two amino acids. Since—with the exception of leucine and isoleucine—the molecular mass of each amino acid is unique, the sequence of the peptide can be reconstructed from the masses of its fragments. 

Many nuclides that are too massive to be stable lose mass by emitting energetic helium nuclei, reducing A by 4 units and Z by 2 units. Energetic helium nuclei are called a particles, so these nuclides undergo a emission. Here are some examples ... 

Figure 8.26(A) is an example of a valve type interface [329]. Helium carrier gas is provided to the headspace saiq)ler and is split into two flow paths. One path is flow-controlled and provides a constant flow of carrier gas which passes from the headspace unit through the heated transfer line to the gas chromatograph. The second flow path is pressure-regulated and, in the standby mode, the seunple loop and seuapling needle are flushed continuously by the helium flow. At a time determined by the operator, the sampling needle pierces the septum and helium pressurizes the headspace vial to any desired pressure. The headspace gas is then allowed to vent through the sample loop. Once filled, the sample loop is placed in series with the normal carrier gas flow and its contents are driv Bbhrough the heated...

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