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Thus, this kind of CNO cycle converts hydrogen to helium slowly, and is called cold CNO cycle. [4] Under conditions of higher temperature and pressure, the rate of proton captures exceeds the rate of beta- decay, pushing the burning to the proton drip line. The essential idea is that a radioactive species will capture a proton before it can beta decay, opening new nuclear burning pathways that ...
New experimental methods and techniques, combined with the development of new theoretical tools, have opened new avenues to explore nuclear reactions of significance for nucleosynthesis at or near the actual temperatures of stellar burning. In particular, many reactions of the cold and hot CNO cycles have been investigated in recent years to provide a complete understanding of this critical ...
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- 3 Min.
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- UNSW Physics
Logarithm of the relative energy output (ε) of proton–proton (PP), CNO and Triple-α fusion processes at different temperatures (T). The dashed line shows the combined energy generation of the PP and CNO processes within a star. At the Sun's core temperature of 15.5 million K the PP process is dominant.
Analyze: As you did with the proton-proton chain, determine the net equation for the CNO cycle. In the space at right, write the equations of the CNO cycle in a column. Then, cross out any substances that appear on both sides. Write the remaining substances at the bottom. This is the net equation for the CNO cycle.
Exercise for you: set the time derivatives of 13N (15O) to zero in the set of equations on page 2. Then eliminate 13N (15O) from the system of equations, allowing us to now approximate the CNO cycle with the following system of equations: Another exercise: Prove the sum of CNO abundances is constant in time.
Only 1.7% of 4 He nuclei being produced in the Sun are born in the CNO cycle. However theoretical models show that the CNO cycle is the dominant source of energy in heavier stars. The CNO process was proposed by Carl von Weizsäcker and Hans Bethe independently in 1938 and 1939, respectively. The reactions of the CNO cycle are :
