Helium special properties

This is what they thought at first. I m giving you a bit of history here. The reaction of beryllium-8 and helium-4 seemed too slow. There was one chance that the reaction speed could be boosted—if carbon-12 had a very special property an energy almost exactly equal to the combined energy of beryllium-8 and helium-4 at temperatures in a red giant. Chemists called this kind of facilitated nuclear reaction resonant. If by some miracle this were true, then the triple-alpha process could work. ... 

The second reason helium and possibly hydrogen clusters are special is their capability to transform to a superfluid state. This is a state in which some or all of the component particles are in their lowest quantum state, a state common to all the particles in that state. This is only possible for particles with integral values of their total spin, particles known as bosons. The common isotope He is one such particle. At a sufficiently low temperature, bulk He goes into its superfluid state, in which a finite fraction of the atoms are in their lowest quantum state. This gives the very cold liquid helium special and sometimes dramatic properties, such as the capability to climb walls of a container, and to spout up through a capillary to form a fountain. 

Compared to the relatively widespread noble gases helium and argon, the noble gases neon, krypton and xenon are less common and harder to obtain. Nevertheless, they are used in a wide range of modem technologies, in particular lighting, optics and electronics, on accoimt of their special properties. They are preferably used in a gaseous state and in mixtures. 

Helium is left out of this list because its light mass lead it to exhibit special properties due to ensuing strong quantum-mechanical effects/zero-point vibrations. 

Tacticity is required for the synthesis of crystalline thin polysilane films used for optical and semiconductor devices. Modern synthetic routes allow control over the conformation and tacticity of polysilane molecules used as precursors for thin layers of photoresists, photoconductors and nonlinear optical phases in complex semiconductor and (opto)electronic devices. These properties can be exploited only if the synthesis method ensures a minimal level of contamination, especially with oxygen and metals, and special care is taken to limit electronic-grade polysilanes to a level of contamination on the order of a few ppm in the case of oxygen and in the ppb range for metals. The reactivity of polysilane toward oxygen has forced placing the devices in a helium environment during measurement procedures.36... 

Starting from a different treatment of double photoionization in helium, based on properties of the wavefunctions in the threshold region, and special coordinates (hyperspherical coordinates) for the description of the correlated motion of the electrons, different predictions for this 0 parameter have been obtained (see [HSW91, KOs92] with references therein).)... 

The Raman spectra of solids have a more or less prominent collision-induced component. Rare-gas solids held together by van der Waals interactions have well-studied CILS spectra [656, 657]. The face-centered, cubic lattice can be grown as single crystals. Werthamer and associates [661-663] have computed the light scattering properties of rare-gas crystals on the basis of the DID model. Helium as a quantum solid has received special attention [654-658] but other rare-gas solids have also been investigated [640]. Molecular dynamics computations have been reported for rare-gas solids [625, 630, 634]. 

A scenario referred to as a sub-Chandrasekhar-mass supernova envisions a C-O WD capped with a helium layer accreted by a companion, and which explodes as the result of a hydrodynamical burning before having reached the Chandrasekhar limit. This type of explosions may exhibit properties which do not match easily the observed properties of typical SNIa events. It cannot be excluded, however, that they are responsible for some special types of events, depending in particular on the He accretion rate and on the CO-sub-Chandrasekhar WD (SCWD) initial mass (e.g. [85]). Unidimensional simulations of He cataclysmics characterized by suitably selected values of these quantities reach the conclusion that the accreted He-rich layer can detonate. Most commonly, this explosion is predicted to be accompanied with the C-detonation of the CO-SC WD. In some specific cases, however, this explosive burning might not develop, so that a remnant would be left following the He detonation. Multidimensional calculations cast doubt on the nature, and even occurrence, of the C-detonation in CO-SC WD (e.g. [86]). 

Among all cases of interest in electrocatalysis, platinum alloys deserve special attention. An interesting report on approximately 70% of platinum mthenium alloys is found in [32]. The annealed surface in this alloy, as shown by LIES, gives a spectrum of approximately 92% of platinum on the surface that is sputtered with helium. The same surface to bulk concentration can be obtained by using argon ions. Even in this case, we can have a catalytic effect (despite having almost entirely platinum in the first layer) because the second layer confers different electronic properties to the uppermost stratum. 

Some of the important facts about condensed helium will now be summarized. The gas first condenses to a liquid known as helium I, the properties of which are not specially remarkable. Below about 2° absolute helium II is formed. This shows a specific heat-temperature relation of the form represented in Fig. 31. The specific heat rises to a sharp peak at 2-19° (38 mm. pressure), the so-called A-point, the excess over the normal in the neighbourhood of this point suggesting an ordered state for helium II, with a rapid decrease in order and increase in entropy as the temperature rises. The general type of behaviour here referred to has already been discussed (p. 310). According to one view, for which, in the hght of the earlier discussion, there is much to be said, helium II possesses an atomic arrangement which has a certain crystalline character. 

The critical amplitudes of atom oscillations in condensed helium are close to those in other rare gases. It follows that the Lindemann criterion (see Chap. 6) cannot be used to explain the special features of helium solidification. In this context, note a remarkable similarity of the changes in the properties of MX and Hc2 caused by the transition from molecular to the soUd state along with an increase in we... 

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