Proton-proton chain reaction
Overveiw of the proton-proton chain.
In the first step in the proton-proton chain, two protons fuse to form a deuterium nucleus. The reaction results in the emission of a positron and a neutrino.
The proton-proton chain is the process of nuclear fusion by which the Sun and other low-mass, main sequence stars generate energy. In essence, the reaction turns four hydrogen nuclei (four protons) into one helium nucleus (an alpha particle).
proton-proton chain The chain of fusion reactions, leading from hydrogen to helium, that powers most main-sequence stars.
Proton-Proton Chain
A series of three nuclear reactions that build a helium atom by adding together protons. The main energy source in our sun.
Protoplanet ...
Proton-Proton Chain
(a) (p-p chain) A series of thermonuclear reactions in which hydrogen nuclei are transformed into helium nuclei. The temperature and density required are about 107 K and 100 g cm-3.
Proton-Proton Chain
CNO Cycle
Sun's Main Sequence Lifespan
Energy Transport in a Star ...
Proton-Proton Chain
A series of nuclear events occurring in the core of a star whereby hydrogen nuclei (protons) are converted into helium nuclei. This process releases energy.
Protoplanet ...
PROTON-PROTON CHAIN
The proton-proton chain is a hypothetical fusion reaction thought to occur deep inside stars. This chain reaction converts hydrogen nuclei into helium nuclei and releases energy (particles) and gamma-rays.
Proton-proton chain: The series of nuclear fusion steps by which the sun converts four hydrogen nuclei into one helium nucleus and thereby generates energy in its core.
The proton-proton chain is more important in stars the mass of the sun or less. Only 1.7% of 4He nuclei being produced in the Sun are born in the CNO cycle.
The proton-proton chain dominates in stars the size of the Sun or smaller.
The CNO cycle dominates in stars heavier than the Sun.
proton-proton chain a nuclear fusion chain reaction used by most stars to generate energy. In a chain process involving three or more reactions, the net result is four hydrogen nuclei are fused together to form a helium nucleus plus energy.
FIGURE: The proton-proton chain illustrated. Protons are grey spheres, neutrons black spheres, the positron and neutrion labeled little black spheres.
Those that are actively fusing hydrogen into helium in the middle, that is, in their cores (either through the proton-proton chain or the carbon cycle), are called "main sequence" stars.
The main reaction operating in the Sun and other low mass MS stars is the Proton-Proton chain (or the p-p chain). To get this reaction to work you need a temperature of at least 13 million K and a density of about 100 gm/cc.
For most stars, this process is dominated by a process called the "proton-proton chain," a sequence of events that transforms four hydrogen atoms into one helium atom.
Stars create energy in one of two ways. The first is converting hydrogen to helium in a proton-proton chain reaction basis(P-P) or the CNO cycle where they convert carbon to nitrogen to oxygen to convert hydrogen to helium(CNO cycle).
It is the start of the proton-proton chain. Gargantuan quantities of protons are fused in this way within the core of the Sun each second.
The net result is:
411H 42He with a release of about 4.4 pJ of energy. (see also Proton-Proton Chain Reaction) [DC99]
Carbon Dating ...
In 1938, Bethe and his colleagues presented a fully developed proton-proton chain of reactions that converts hydrogen into helium, which would allow the Sun to shine for about 10 billion years.
The simplest is the proton-proton chain, which occurs in stars having core temperatures less than 15 x 10^6 K. The proton- proton chain uses two steps to convert Hydrogen first into 3He, and then combines two 3He nuclei into He, and giving back 2 H.
Stars begin as a cloud of mostly hydrogen with about 25% helium and heavier elements in smaller quantities. In the Sun, with a 107 K core, hydrogen fuses to form helium in the proton-proton chain: ...
The temperature of the core region continues to increase until it reaches a level high enough to support thermonuclear reactions--the proton-proton chain or the carbon cycle.
 See also: Energy, Hydrogen, Helium, Sun, Proton
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