Helium from nuclear fusion

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 ... 

Helium-3 [14762-55-1], He, has been known as a stable isotope since the middle 1930s and it was suspected that its properties were markedly different from the common isotope, helium-4. The development of nuclear fusion devices in the 1950s yielded workable quantities of pure helium-3 as a decay product from the large tritium inventory implicit in maintaining an arsenal of fusion weapons (see Deuterium AND TRITIUM) Helium-3 is one of the very few stable materials where the only practical source is nuclear transmutation. The chronology of the isolation of the other stable isotopes of the hehum-group gases has been summarized (4). 

No doubt Chadwick and Rutherford would have been quick to pronounce similarly on the experiments of Pons and Fleischmann, a who announced on 23 March 1989 that they had observed I sustained nuclear fusion from the electrolysis of heavy water using palladium electrodes. Deuterium is absorbed by palladium in the same way as hydrogen, but its fusion into helium does not require such extreme conditions (see page 109). All the same, these conditions have long proved impossible to sustain in physicists attempts to harness nuclear fusion for energy generation. Now two chemists were claiming that these massively expensive fusion projects could be abandoned all you needed was a test tube and two strips of palladium. 

The mass of each nucleon in a hydrogen-2 nucleus is greater than the mass of each nucleon in a helium-4 nucleus, which results from the fusion of two hydrogen-2 nuclei. This lost mass has been converted to energy, which is why nuclear fusion is an eneigy-releas-ing process. 

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. 

Hydrogen bomb—An nuclear explosive weapon which uses hydrogen isotopes as fuel and an atom bomb as a detonator. More powerful than an atom bomb, the Hydrogen bomb derives its destructive power from energy released when nuclei of hydrogen are forced together to form helium nuclei in a process called nuclear fusion. Also called H-bomb or Thermonuclear bomb. 

Our sun supplies energy to the earth from a distance of 93,000,000 miles. Like other stars, it is a giant nuclear fusion reactor. Much of its energy comes from the fusion of deuterium, H, producing helium, He. 

Figure 2.1 shows the dependence of element abundances on atomic number for the cosmos. In cosmochemistry, such abundances are always presented as a ratio— number of atoms of the respective element/10 atoms silicon—in order to eliminate the influence of the strongly varying concentrations of hydrogen and helium. The remarkable drop in abundance from atomic number 47 onward indicates the boundary between elements formed by nuclear fusion and those built up by subsequent neutron absorption reactions. Maxima are always related to especially high nuclear stability of the respective element (a typical example is the iron peak). 

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... 

Where did the carbon come from The universe is primarily composed of hydrogen, with lesser amounts of helium, and comparatively little of the heavier elements (which are collectively termed metals by astronomers). The synthesis of elements from the primordial hydrogen, which was formed from the fundamental particles upon the initial stages of cooling after the Big Bang some 15 Gyr ago, is accomplished by nuclear fusion, which requires the high temperatures and pressures within the cores of stars. Our Sun is relatively small in stellar terms, with a mass of c.2 X 1030kg, and is... 

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