Hydrogen fusion

Deuterium is used as a moderator to slow down neutrons. Tritium atoms are also present but in much smaller proportions. Tritium is readily produced in nuclear reactors and is used in the production of the hydrogen (fusion) bomb. It is also used as a radioactive agent in making luminous paints, and as a tracer. 

The first hydrogen (fusion) bomb to be tested by the United States is exploded at Bikini Atoll. 

The pressure exerted by the radiation escaping from inner portions of the star counteracts the force of gravity, and the balance of the two opposing forces keeps the volume of the star constant as long as hydrogen fusion continues. 

Separation of 6Li from natural abundance (7.4%) feed to synthesize 6LiD (an important component of the fuel used in hydrogen fusion weapons (hydrogen bombs)). This, because the (n,T) cross section for 6Li is much larger than that of 7Li, so production of tritium is much enhanced in the triggering explosion. 

In stars with masses greater than 1.2 times the solar mass, hydrogen fusion proceeds via another channel, the so-called CNO cycle. This process tags together proton captures and () decays in the following chain of reactions ... 

The emission of a helium nucleus in the final stage regenerates the initial carbon-12. The latter thus plays the role of a catalyst. The overall result is the fusion of four protons into a helium nucleus. At high temperatures, this cycle dominates over the proton-proton chain. Indeed thermal agitation facilitates penetration of the relatively high electrical barrier between proton and carbon nucleus. Whatever hydrogen fusion mechanism is prevalent, the star s mass determines the rate at which it consumes its nuclear fuel, and hence also its lifetime. The higher its mass, the more quickly it bums. 

Hydrogen fusion via either the proton-proton chain or the CNO cycle in the centre of stars comes to an end when most of the hydrogen has been transformed into helium. Helium fusion produces two elements essential to life, namely carbon and oxygen. In fact, carbon constitutes 18% of our bodies, and oxygen 65%, whilst the fractions of these same elements in solar material are just 0.39% and 0.85%, respectively. Only hydrogen and helium are more abundant in the Sun. 

In the first step of hydrogen fusion, two protons combine to form a deuteron and a positron. A deuteron is the nucleus of an isotope of hydrogen heavy hydrogen, or deuterium. It consists of a proton and a neutron. 

The patent was rejected on the grounds that it was too sketchy to be comprehensible. The work foundered, and it was soon discovered that the helium was not produced by fusion at all. It was being absorbed from the atmosphere into the glass walls of the vessels used for the experiments. In 1930, no lesser authorities than James Chadwick and Ernest Rutherford dismissed the claims of hydrogen fusion, saying The presence of an element has been mistaken for its creation. ... 

Table 1 Logarithms of mass fractions for abundant elements in four classical sdo stars and in the sun. Col. 6 gives theoretical predictions from hydrogen fusion in the CNO cycle at T = 2 10 K...

The coolest stars with just enough mass to fuse hydrogen are the M-dwarfs (see chapter 3). Two new classes of brown dwarfs have been added to the cool end of the stellar spectrum. The L-dwarfs (1,300 to 2,000 Kelvin) are slightly cooler and less massive than M-dwarfs. T-dwarfs are cooler and lighter than the L-dwarfs. Both of these new dwarfs cannot sustain hydrogen fusion. Researchers have recently discovered hundreds of T-dwarfs and tens of L-dwarfs. Even the cool T-dwarfs may have magnetic fields that create occasional stellar flares. [For more information, see Linda Rowan, Cooler dwarf stars, Science 289(5480) 697 (August 4, 2000).]... 

Gamow s research career focused on two major fields, seemingly about as far apart as one can imagine nuclear physics and astronomy. In his work on nuclear physics, he devised explanations for two ways in which nuclei can decay, by the loss of alpha particles and by the emission of beta particles. During World War II, he was a member of the Manhattan Project, the program for the development of the first atomic (fission) bomb, and he was later involved in work on the first hydrogen (fusion) bomb. 

We have found expressions for the central temperature of a star. This must be greater than the ignition temperature for the hydrogen fusion if a star is to result. For a perfect gas, the pressure given by Eq. (93) must be the same as that given by the equation of state. Equating the pressures gives... 

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