Helium-4, from fusion reactions

Scientists are searching for a way to harness the energy from fusion reactions. Fusion is a more desirable way to produce energy than fission. The main product of fusion, helium, is relatively harmless compared with the radioactive products of fission. Unfortunately, fusion is proving more difficult than fission to harness. 

An a particle can abstract two electrons from some other atom or molecule (and given the extremely high ionization potential of helium, the highest of any atom, it would be difficult to prevent it) to become a helium atom. Helium also is a constituent in stars as a result of the fusion reaction... 

Figuratively speaking, just as hydrogen is said to bum, we may say that helium is the ash left over from the reaction. The imponderable separates from the ponderous, photons and neutrinos take flight, leaving the heavy helium ash to accumulate gradually. The ample energy disgorged (26.7 MeV) makes this reaction chain one of the most generous known. For example, thermonuclear fusion of 1 g of hydrogen releases some 20 milhon times more energy than the chemical combustion of 1 g of coal.

A potential major source of energy for the mid- to late-21st century is nuclear fusion. In todays experimental fusion reactors, deuterium and tritium atoms (both isotopes of hydrogen) fuse to create helium and fast-flying neutrons. The neutrons escape from the reaction chamber, carrying with them vast amounts of kinetic energy. 

As in nuclear fission, incredible amounts of energy are produced from relatively small amounts of materials. From a raw materials point of view, nuclear fusion is ideal. Hydrogen and helium are readily available fusion reactants. Fusion reactions power the sun, which helps to explain the difficulty in creating the conditions that would allow fusion to take place. The astronomically high temperatures required present technical problems that may never be resolved. 

The energy of the Sun and stars comes from nuclear fusion reactions, which have the overall effect of transforming hydrogen nuclei to alpha particles (helium nuclei). The temperature of the particular star determines the mechanism by which this transformation takes place. The Sun, a moderately small star, is thought to be powered by the following sequence of reactions ... 

It is clear, for example from radio-carbon dating of rocks in the earth s surface, that the solar system must be very much older than the Kelvin age of 3 x 107 years. It is now taken for granted that the main source of stellar energy comes from nuclear reactions. The fusion of four protons (hydrogen nuclei) to an alpha-particle (helium nucleus) is associated with the release of energy Q, where Q k, 26 MeV. The total available energy is thus... 

Solar fusion Nuclear fusion reactions are responsible for the glow and heat from stars such as the Sun. The temperature of the Sun s core Is about 15,000,000 K. It is so hot and dense that hydrogen nuclei fuse to produce helium. After billions of years, the Sun s hydrogen will be mostly depleted. Its temperature will rise to about 100,000,000 K, and the fusion process will then change helium into carbon. 

Most stars gradually cool and dim as the helium is converted to carbon and oxygen, ending their lives as white dwarfs. In stars that are 10 or more times more massive than our Sim, however, a more dramatic fete awaits. The extreme mass of these stars leads to much higher temperatures and pressures at the core, where a rariety of fusion processes lead to synthesis of the elements from neon to sulfur. These fusion reactions are collectively called advanced burning. 

There are two different kinds of nuclear weapons. Weapons based on the fission process ( atomic bombs ) and weapons based on the nuclear fusion reaction ( hydrogen bombs ). The fusion weapons get most of their energy from a fusion process of fight nuclides (like deuterium) to helium. Fusion weapons contain a small fission bomb that serves to heat the fusion matter to a temperature of about 10 K required for the start of the fusion process. 

Helium (He) is the only substance that remains liquid under its own pressure at the lowest temperature recorded. There are only about five parts per miUion of helium in the Earth s atmosphere, but it reaches substantially higher concentrations in natural gas, from which it is obtained. Helium is formed from the radioactive decay of heavy elements. For example, a kilogram of uranium gives 865 L of helium after complete decay. There s not much helium on Earth, but there is a lot in the universe. About 23% of the known mass of the universe is helium, mostly produced by thermonuclear fusion reactions between hydrogen nuclei in stars. So, an outside observer of our universe (whatever that means ) would probably conclude that helium is some of the most important stuff around. 

After hydrogen. He is the second most abundant element in the universe. It occurs to an extent of <7% by volume in natural gas from sources in the US and Canada, and this origin is doubtless from the radioactive decay of heavier elements (a-particle = 2He). Helium is also found in various minerals containing a-emitting unstable isotopes. Helium was first detected spectroscopically in the Sun s atmosphere. Nuclear fusion reactions taking place in the Sun start at temperatures above 10 K, and the following reactions are... 

The cylinder is removed to storage area (B). The optimum reaction temperature profile for a fusion reaction will depend on the reactivity of the samples. The furnace temperature was programmed from 100 to 300°C over a period of 10 min. As the reaction occurs, the volatile reaction products and water, liberated from the molten mixture, are carried by the flowing helium carrier gas and concentrated in the trap. At the end of the reaction period, i.e. 

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