Protons nuclear fusion

The ordinary isotope of hydrogen, H, is known as Protium, the other two isotopes are Deuterium (a proton and a neutron) and Tritium (a protron and two neutrons). Hydrogen is the only element whose isotopes have been given different names. Deuterium and Tritium are both used as fuel in nuclear fusion reactors. One atom of Deuterium is found in about 6000 ordinary hydrogen atoms. 

Nuclear Fusion Reactions. Tritium reacts with deuterium or protons (at sufftciendy high temperatures) to undergo nuclear fusion ... 

At 2000 K there is sufficient energy to make the H2 molecules dissociate, breaking the chemical bond the core density is of order 1026 m-3 and the total diameter of the star is of order 200 AU or about the size of the entire solar system. The temperature rise increases the molecular dissociation, promoting electrons within the hydrogen atoms until ionisation occurs. Finally, at 106 K the bare protons are colliding with sufficient energy to induce nuclear fusion processes and the protostar develops a solar wind. The solar wind constitutes outbursts of material that shake off the dust jacket and the star begins to shine. 

Nuclear fusion processes derive energy from the formation of low-mass nuclei, which have a different binding energy. Fusion of two nuclear particles produces a new nucleus that is lighter in mass than the masses of the two fusing particles. This mass defect is then interchangeable in energy via Einstein s equation E = me2. Specifically, the formation of an He nucleus from two protons and two neutrons would be expected to have mass ... 

Hydrogen atoms and part of He are believed to have been created during the Big Bang by proton-electron combinations. Most nuclides lighter than iron were created by nuclear fusion reactions in stellar interiors (cf table 11.1). Nuclides heavier than the Fe-group elements (V, Cr, Mn, Fe, Co, Ni) were formed by neutron capture on Fe-group seed nuclei. Two types of neutron capture are possible slow (s-process) and rapid (r-process). 

Proton-proton fusion chain reactions (Bethe and Critchfield 1938) the first long-lived intermediate of nuclear fusion in low-mass stars, He, adds to one He to yield (radioactive) Be which eventually produces two He by capture of another proton and radioactive decay of B (pp-111 chain) or vice versa along the Be decay product Li -l- p (pp-11). 

Nuclear fusion is the process by which two light atomic nuclei combine to form one heavier atomic nucleus. As an example, a proton (the nucleus of a hydrogen atom) and a neutron will, under the proper circumstances, combine to form a deuteron (the nucleus of an atom of heavy hydrogen )- In general, the mass of the heavier product nucleus is less than the total mass of the two lighter nuclei. 

When a proton and neutron combine, for example, the mass of the resulting deuteron is 0.00239 atomic mass unit less than the total mass of the proton and neutron combined. This loss of mass is expressed in the form of 2.23 MeV (million electron volts) of kinetic energy of the deuteron and other particles and as other forms of energy produced during the reaction. Nuclear fusion reactions are like nuclear fission reactions, therefore, in the respect that some quantity of mass is transformed into energy. 

The particles most commonly involved in nuclear fusion reactions include the proton, neutron, deuteron, a triton (a proton combined with two neutrons), a helium-3 nucleus (two protons combined with a neutron), and a helium-4 nucleus (two protons combined with two neutrons). Except for the neutron, all of these particles carry at least one positive electrical charge. That means that fusion reactions always require very large amounts of energy in order to overcome the force of repulsion between two like-charged particles. For example, in order to fuse two protons with each other, enough energy must be provided to overcome the force of repulsion between the two positively charged particles. 

The Bethe carbon-cycle is by no means the only nuclear fusion reaction that one might conceive. A more direct approach, for example, would be one in which two protons fuse to form a deuteron. That deuteron could, then, fuse with a third proton to form a helium-3 nucleus. Finally, the helium-3 nucleus could fuse with a fourth proton to form a helium-4 nucleus. The net result of this sequence of reactions would be the combining of four protons (hydrogen nuclei) to form a single helium-4 nucleus. The only net difference between this reaction and Bethe s carbon cycle is the amount of energy involved in the overall set of reactions. 

The probability of the formation of higher atomic number elements, like tungsten, by absorption of neutrons and/or protons during a star evolution and subsequent super nova blast is quite low. Therefore, the abundances of higher atomic number elements are considerably smaller, as for the elements which were formed by nuclear fusion reactions in an evoluting star. 

Explain why achievement of nuclear fusion in the laboratory requires a temperature of about 100 million degrees Celsius, which is much higher than that in the interior of the sun (15 million degrees Celsius). Tritium contains one proton and two neutrons. There is no proton-proton repulsion present in the nucleus. Why, then, is tritium radioactive ... 

Nuclear energy, which is obtained when nucleons (protons and neutrons) are allowed to adopt lower energy arrangements and to release the excess energy as heat, does not contribute to the carbon dioxide load of the atmosphere, but it does present pollution problems of a different land radioactive waste. Optimists presume that this waste can be contained, in contrast to the burden of carbon dioxide, which spreads globally. Pessimists doubt that the waste can be contained—for thousands of years. Nuclear power depends directly on the discipline of chemistry in so far as chemical processes are used to extract and prepare the uranium fuel, to process spent fuel, and to encapsulate waste material in stable glass blocks prior to burial. Nuclear fusion, in contrast to nuclear fission, does not present such serious disposal-related problems, but it has not yet been carried out in an economic, controlled manner. 

A detailed account of these problems is beyond the scope of this book, despite their fascination. Many aspects of the arguments are accessible only to specialists, but even a superficial reading of the above sources makes it clear that most cosmic events such as nuclear fusion, element formation, and formation, coalescence, and decay of black holes actually generate enormous amounts of entropy, relative to processes familiar to us on Earth. The major factor responsible for this, omitted in simplified accounts such as given above, is that we must take into account not only neutrons, protons, etc., but the enormous number of massless particles generated, such as photons and neutrinos. When this is done, the entropy balance is profoundly changed. 

Large amounts of energy are emitted as the result of another type of nuclear process called nuclear fusion. In nuclear fusion, nuclei of two light elements collide at velocities high enough to overcome the mutual repulsion of the nuclear protons, and fuse to form a nucleus of larger atomic number. 

This stage of nuclear fusion is called helium burning. Notice that carbon, element 6, is formed without prior formation of elements 3,4, and 5, explaining in part their unusually low abundance. Nitrogen is relatively abundant because it can be produced from carbon through a series of reactions involving proton capture and positron emission. 

On March 23, 1989, the University of Utah held a press conference that shook the energy world. Electrochemists Stanley Pons and Martin Fleischmann announced reproducible cold fusion 10% more energy released than supplied. They passed an electric current through palladium and platinum wires in a container of heavy water and lithium sulfate. Cold fusion is nuclear fusion at ambient temperature. When the two hydrogen atoms in a water molecule are replaced with deuterium (called heavy hydrogen because it has one proton and one neutron), it is called heavy water. 

---