Helium determination

Photolysis of CfJlm and C6(pis in n-Hexane Under Helium Determination of the Kinetic Isotope Effect... 

Aqueous samples purged by an inert gas analyte trapped on a sorbent trap transferred onto a GC column by heating the trap and backflushing with helium determined by GC/MS. 

If the gas is either hydrogen or helium, determine adjusted critical constants from the empirical formulas... 

Modern airships use helium to provide lift. The Hindenburg used hydrogen gas, which provides about twice the lift of helium but is no longer used because it is extremely flammable. The hehum is contained in bags made of a space-age, leakproof fabric called Tedlar, a type of plastic. The bags are loosely inflated so that the helium pressure is about the same as atmospheric pressure. The quantity of helium determines the lifting ability of the ship. 

Butt, C.R.M. and Gole, M.J., 1984. Helium determinations in mineral exploration. Aust. Dept. Resources and Energy, Report no. NERDDP/EG/84/271,351 pp. 

While idly dreaming over these equations (theoretieians eall it working ) we might happen to notiee that the linear eombination (9-24b) we have seleeted for ground-state helium is the same as the expansion of a 2 x 2 determinant... 

Liquid helium s use in magnetic resonance imaging (MRI) continues to increase as the medical profession accepts and develops new uses for the equipment. This equipment has eliminated some need for exploratory surgery by accurately diagnosing patients. Another medical application uses MRE to determine (by blood analysis) whether a patient has any form of cancer. 

Fourteen isotopes are now recognized. 258Md has a half-life of 2 months. This isotope has been produced by the bombardment of an isotope of einsteinium with ions of helium. Eventually enough 258Md should be made to determine its physical properties. 

Solid covalent dinitrogen pentoxide can be prepared by freezing the vapour with liquid helium. Normally, solid dinitrogen pentoxide exists as (NO2+) (NOj ), showing absorption bands in its Raman spectrum only at 1050 and 1400 cm the structure of this form has been determined by X-ray crystallography. ... 

The methods of choice for beryUium oxide in beryUium metal are inert gas fusion and fast neutron activation. In the inert gas fusion technique, the sample is fused with nickel metal in a graphite cmcible under a stream of helium or argon. BeryUium oxide is reduced, and the evolved carbon monoxide is measured by infrared absorption spectrometry. BeryUium nitride decomposes under the same fusion conditions and may be determined by measurement of the evolved nitrogen. Oxygen may also be determined by activation with 14 MeV neutrons (20). The only significant interferents in the neutron activation technique are fluorine and boron, which are seldom encountered in beryUium metal samples. 

Hot atom reactions have also been used to label organic compounds with T. Irradiation of helium-3 with neutrons according to the nuclear reaction produces very energetic tritium atoms that can displace ordinary hydrogen in organic compounds. This procedure is not very selective, and the labeling pattern must be determined to enable the tritiated product to be used effectively as a tracer (34). 

In the dynamic method the powder is flushed with an inert gas during degassing, nitrogen is then adsorbed on the powder in a carrier of helium gas at known relative pressure while the powder is in a container surrounded by hquid nitrogen. The changing concentration of nitrogen is measured by a cahbrated conductivity cell so that the amount adsorbed can be determined. 

Elastic recoil spectrometry (ERS) is used for the specific detection of hydrogen ( H, H) in surface layers of thickness up to approximately 1 pm, and the determination of the concentration profile for each species as a function of depth below the sample s surfece. When carefully used, the technique is nondestructive, absolute, fast, and independent of the host matrix and its chemical bonding structure. Although it requires an accelerator source of MeV helium ions, the instrumentation is simple and the data interpretation is straightforward. 

ITie BET method is the most widely used procedure for determining the surface area of porous materials. In this chapter, BET results were obtained from single point measurements using a Micromeritics Flowsorb II 2300 surface area analyzer. A mixture of nitrogen in helium (30 70 mole percentage) was used. Although this simple method is not quantitative for the microporous materials studied in section 5, it still allows qualitative comparisons to be made. 

These observations consummated in a growth model that confers on the millions of aligned zone 1 nanotubes the role of field emitters, a role they play so effectively that they are the dominant source of electron injection into the plasma. In response, the plasma structure, in which current flow becomes concentrated above zone 1, enhances and sustains the growth of the field emission source —that is, zone 1 nanotubes. A convection cell is set up in order to allow the inert helium gas, which is swept down by collisions with carbon ions toward zone 1, to return to the plasma. The helium flow carries unreacted carbon feedstock out of zone 1, where it can add to the growing zone 2 nanotubes. In the model, it is the size and spacing of these convection cells in the plasma that determine the spacing of the zone 1 columns in a hexagonal lattice. 

The first ab initio smdy of an interaction polarizability was that of O Brien et al. (1973) on a pair of helium atoms. They obtained /0(r) for the range r = 3.5ao through lOao- The experimentally determined value of is negative, which suggests that the incremental mean pair polarizability must be negative around the minimum in the potential curve. 

An experiment is performed to determine the vapor pressure of formic acid. A 30.0-L volume of helium gas at 20.0°C is passed through 10.00 g of liquid formic acid (HCOOH) at 20.0°C. After the experiment, 7.50 g of liquid formic acid remains. Assume that the helium gas becomes saturated with formic acid vapor and the total gas volume and temperature remain constant. What is the vapor pressure of formic acid at 20.0°C ... 

This means that most of the mass of the atom must be furnished by the nucleus. However, the mass of the nucleus is not determined by the number of protons alone. For example, a helium nucleus has two protons and a hydrogen nucleus has one proton. Yet a helium atom is measured to be four times heavier than a hydrogen atom. What can be the composition of the helium nucleus A partial answer to this problem was obtained when a third particle, the neutron, was... 

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