Helium. .. Element

Unless specified, samples were from soot deposited on the chamber wall and the buffer gas was helium. Elements are those incorporated in the graphite anode, D is the nanotube diameter range, D, p is the most abundant nanotube diameter, and Crystallites refers to metal-containing particles generated by the arc process and found in the soot. 

If you could travel through the universe to collect samples of matter, you would find 92 naturally occurring elements. The amount of each element would vary from location to location. Helium, which is the second most common element in the universe, is much less abundant here on Earth. Oxygen is the most abundant element on Earth. Per kilogram of Earth s crust, there are 4.64 x 10 mg of oxygen, but only 8 X 10 mg of helium. Elements with atomic numbers greater than 92 do not exist in nature. These synthetic elements must be created in laboratories or nuclear reactors. 

Radioactive elements may often be prepared artificially by bombarding the atoms of ordinary stable elements with, e.g. helium nuclei. See radioactivity, artificial. 

Gr. helios, the sun). Janssen obtained the first evidence of helium during the solar eclipse of 1868 when he detected a new line in the solar spectrum. Lockyer and Frankland suggested the name helium for the new element. In 1895 Ramsay discovered helium in the uranium mineral clevite while it was independently discovered in cleveite by the Swedish chemists Cleve and Langlet at about the same time. Rutherford and Royds in 1907 demonstrated that alpha particles are helium nuclei. 

Except for hydrogen, helium is the most abundant element found through out the universe. Helium is extracted from natural gas. In fact, all natural gas contains at least trace quantities of helium. 

Helium has the lowest melting point of any element and is widely used in cryogenic research because its boiling point is close to absolute zero. Also, the element is vital in the study of super conductivity. 

While helium normally has a 0 valence, it seems to have a weak tendency to combine with certain other elements. Means of preparing helium difluoride have been studied, and species such as HeNe and the molecular ions He+ and He++ have been investigated. 

Dmitri Mendeleev) Mendelevium, the ninth transuranium element of the actinide series discovered, was first identified by Ghiorso, Harvey, Choppin, Thompson, and Seaborg in early in 1955 during the bombardment of the isotope 253Es with helium ions in the Berkeley 60-inch cyclotron. The isotope produced was 256Md, which has a half-life of 76 min. This first identification was notable in that 256Md was synthesized on a one-atom-at-a-time basis. 

Ernest O. Lawrence, inventor of the cyclotron) This member of the 5f transition elements (actinide series) was discovered in March 1961 by A. Ghiorso, T. Sikkeland, A.E. Larsh, and R.M. Latimer. A 3-Mg californium target, consisting of a mixture of isotopes of mass number 249, 250, 251, and 252, was bombarded with either lOB or IIB. The electrically charged transmutation nuclei recoiled with an atmosphere of helium and were collected on a thin copper conveyor tape which was then moved to place collected atoms in front of a series of solid-state detectors. The isotope of element 103 produced in this way decayed by emitting an 8.6 MeV alpha particle with a half-life of 8 s. 

When hydrogen is burned up in the nuclear furnace of a star, helium burning takes over, forming carbon, which in turn leads to oxygen, etc. Subsequent emission processes releasing a-particles, equilibrium processes, neutron absorption, proton capture, etc. lead to heavier elements. 

As the universe expanded it cooled and the positively charged protons and helium nuclei com bined with electrons to give hydrogen and helium atoms Together hydrogen and helium account for 99% of the mass of the universe and 99 9% of its atoms Hydrogen is the most abundant element 88 6% of the atoms in the universe are hydrogen and 11 3% are helium... 

Sometimes a star explodes in a supernova cast mg debris into interstellar space This debris includes the elements formed during the life of the star and these elements find their way into new stars formed when a cloud of matter collapses in on itself Our own sun is believed to be a second generation star one formed not only from hydrogen and helium but containing the elements formed in earlier stars as well... 

The period (or row) of the periodic table m which an element appears corresponds to the principal quantum number of the highest numbered occupied orbital (n = 1 m the case of hydrogen and helium) Hydrogen and helium are first row elements lithium in = 2) IS a second row element... 

Noble gases (Section 1 1) The elements in group VIIIA of the penodic table (helium neon argon krypton xenon radon)... 

Many elements are familiar to us in everyday life. Iron is an element used for making ships, cars, spades, etc. There are about 90 such familiar elements, including helium, oxygen, nitrogen, mercury, platinum, and gold. As an element, iron consists of atoms of iron, the smallest building blocks, each of which is indivisible by chemical means. A lump of iron comprises millions, trillions, and zillions of atoms, and the mass of each atom of iron is very small, about 10 g In a piece of iron weighing 50 g, there are about lO atoms. 

Similarly, emits seven helium nuclei and 4 beta particles during its transition through several other elements, until Pb is reached and Th starts the successive elimination of six helium nuclei and 4 beta particles, which leads to Pb. 

At the sorts of temperatures that exist normally on earth, all matter is made up from about 90 elements. Most of these elements are familiar, such as solid iron, liquid mercury, and gaseous helium. 

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. 

For each element, the number of protons is fixed. Thus, for hydrogen (Z = 1) there is just one proton (P = 1) for the next element, helium (Z = 2), there are just two protons (P = 2) and so on up to the heaviest natural element, uranium, which has atomic number 92 and therefore has Z = P = 92. 

Extraterrestrial dust particles can be proven to be nonterrestrial by a variety of methods, depending on the particle si2e. Unmelted particles have high helium. He, contents resulting from solar wind implantation. In 10-)J.m particles the concentration approaches l/(cm g) at STP and the He He ratio is close to the solar value. Unmelted particles also often contain preserved tracks of solar cosmic rays that are seen in the electron microscope as randomly oriented linear dislocations in crystals. Eor larger particles other cosmic ray irradiation products such as Mn, Al, and Be can be detected. Most IDPs can be confidently distinguished from terrestrial materials by composition. Typical particles have elemental compositions that match solar abundances for most elements. TypicaUy these have chondritic compositions, and in descending order of abundance are composed of O, Mg, Si, Ee, C, S, Al, Ca, Ni, Na, Cr, Mn, and Ti. 

Elemental chemical analysis provides information regarding the formulation and coloring oxides of glazes and glasses. Energy-dispersive x-ray fluorescence spectrometry is very convenient. However, using this technique the analysis for elements of low atomic numbers is quite difficult, even when vacuum or helium paths are used. The electron-beam microprobe has proven to be an extremely useful tool for this purpose (106). Emission spectroscopy and activation analysis have also been appHed successfully in these studies (101). 

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