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Atom in Modern Science
65
sun, the temperature increases gradually from 6000° C. at the surface to twenty million degrees in the centre.
Two nuclear physicists, H. Bet he and C. Weizsäcker, simultaneously found out that the nuclear process known as "carbon cycle" is responsible for the energy production in the sun. This thermonuclear process is not limited to a single nuclear transformation, but consists of a sequence of transformations forming a reaction chain. A most important feature of this process is that it is a closed circuit, returning to the starting point after every six steps. The main participants of the process are the nuclei of carbon and of nitrogen, together with protons with which they collide.
Briefly the cycle is: (1) A proton on colliding with an atom of normal carbon (C12) liberates some subatomic energy in the form of gamma rays and transforms the atom to the lighter isotope of nitrogen (N13).
(2) The nucleus of N13 being unstable adjusts itself by emitting a positive electron, or positive beta particle and becoming the stable nucleus of the heavier isotope or carbon (C13) which is known to be present in small quantities in ordinary coal.
(3) This carbon isotope collides with another proton and is transformed into normal nitrogen (N14) with additional release of energy in the form of gamma rays.
(4) In the next step, the nucleus of nitrogen collides with still another proton (third) and gives rise to an unstable oxygen isotope (015).
(5) Which very rapidly transforms into stable Ni5 by emitting a positron.
(6) Finally Ni5 receiving in its heart the fourth proton, splits into two unequal parts one of which is the C12 nucleus with which the process started and the other is a helium nucleus or alpha particle which is composed of two protons and two neutrons. The same result would have been obtained if the process was started with normal nitrogen atom instead of carbon.
