Liquid helium properties

Nevertheless, the simplest way to produce low temperature is still the use of cryoliquids (e.g. nitrogen, helium). It must be considered that most low-temperature equipments existing in a laboratory are designed for the use with cryoliquids, and the change to the new technologies is definitely expensive. Also for this reason, we shall briefly describe the properties and the use of cryoliquids used in low-temperature experiments and in particular helium (liquid or gas as used in pulse tubes) which practically intervenes in all refrigeration processes below 10 K. 

Saturated liquid property at 0.1 MPa Helium-4 Hydrogen" Neon Nitrogen Air Fluorine Argon Oxygen Methane... 

Kamerlingh Onnes had only a thimbleful of helium liquid, but it was to be the grand overture to his explorations in a vast new temperature region, a place of intense cold where the physical properties of many substances changed remarkably. Even at the temperature of liquid air, one could perform strange tricks. One can, for example, mold... 

Unlike water, sodium, or helium, liquid fluoride salts are a family of coolants with similar general properties. The choice of a specific molten salt for a specific application is determined by functional requirements and costs. Many salts have been examined. Table XXVI-3 shows the properties for several different liquid salts and traditional reactor coolants under typical conditions. Table XXVI-4 lists leading candidates for various nuclear liquid salt applications and their key physical properties. The remainder of this Appendix discusses the various salts and the constraints that limit the choice of salt. 

It has other peculiar properties. Helium is the only liquid that cannot be solidified by lowering the temperature. It remains liquid down to absolute zero at ordinary pressures, but it can readily be solidified by increasing the pressure. Solid 3He and 4He are unusual in that both can be changed in volume by more than 30% by applying pressure. 

Cathodoluminescence microscopy and spectroscopy techniques are powerful tools for analyzing the spatial uniformity of stresses in mismatched heterostructures, such as GaAs/Si and GaAs/InP. The stresses in such systems are due to the difference in thermal expansion coefficients between the epitaxial layer and the substrate. The presence of stress in the epitaxial layer leads to the modification of the band structure, and thus affects its electronic properties it also can cause the migration of dislocations, which may lead to the degradation of optoelectronic devices based on such mismatched heterostructures. This application employs low-temperature (preferably liquid-helium) CL microscopy and spectroscopy in conjunction with the known behavior of the optical transitions in the presence of stress to analyze the spatial uniformity of stress in GaAs epitaxial layers. This analysis can reveal,... 

The second observation is that the EB-curable adhesive resins show no change in adhesive properties from liquid helium temperatures up to temperatures Just below their service temperatures. This can be seen for the adhesives, EB2000 and 1 1L. At this time there is no explanation for this behavior. 

H. Kamerlingh Onnes (Leiden) properties of matter at low temperatures and production of liquid helium. 

The availability of large quantities of liquid helium as well as an excellent support staff led to the undertaking of many experiments at 8 K (the boiling temperature of helium) as well as the lower temperatures obtained by pumping. One subset was the measurement of the resistivity (conductivity) of metals, since this property was useful as a secondaiy thermometer. Although a linear decline was obseived, various speculations were made as to what the result would be when zero absolute temperature was reached. In April 1911 came the surprising discoveiy that the resistivity in mercury disappeared. At first the sur-... 

The behavior of a multi-particle system with a symmetric wave function differs markedly from the behavior of a system with an antisymmetric wave function. Particles with integral spin and therefore symmetric wave functions satisfy Bose-Einstein statistics and are called bosons, while particles with antisymmetric wave functions satisfy Fermi-Dirac statistics and are called fermions. Systems of " He atoms (helium-4) and of He atoms (helium-3) provide an excellent illustration. The " He atom is a boson with spin 0 because the spins of the two protons and the two neutrons in the nucleus and of the two electrons are paired. The He atom is a fermion with spin because the single neutron in the nucleus is unpaired. Because these two atoms obey different statistics, the thermodynamic and other macroscopic properties of liquid helium-4 and liquid helium-3 are dramatically different. 

Let us first consider physical systems, in which quantum effects might be important, in order of decreasing effect. The prototype quantum liquid is liquid helium with its well-known exotic properties. This liquid requires a full quantum... 

Tchouar, N. Ould-Kaddur, F. Levesque, D., Computation of the properties of liquid neon, methane, and gas helium at low temperature by the Feynman-Hibbs approach, J. Chem. Phys. 2004,121, 7326-7331... 

The properties of the two helium isotopes in the liquid state are strongly influenced by quantum effects. In Fig. 2.8, the specific heat of 3He, calculated from the ideal gas Fermi model (Tp = 4.9 K) with the liquid 3He density, is compared with the experimental data. The inadequacy of this model is evident. A better fit, especially at the lower temperatures, is obtained by the Landau theory [25]. 

J. White The Properties of Liquid and Solid Helium, Clarendon, Oxford (1967)... 

The density of He I at the boiling point at 1 atm is 125 kg m 3 and the viscosity is 3 x 10 6 Pa s. As we would anticipate, cooling increases the viscosity until He II is formed. Cooling this form reduces the viscosity so that close to 0 K a liquid with zero viscosity is produced. The vibrational motion of the helium atoms is about the same or a little larger than the mean interatomic spacing and the flow properties cannot be considered in classical terms. Only a quantum mechanical description is satisfactory. We can consider this condition to give the limit of De-+ 0 because we have difficulty in defining a relaxation when we have the positional uncertainty for the structural components. 

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