IGNOU PHE 15 2018 - Explain triple α-reaction. Also discuss its significance in resp

Question

Explain triple α-reaction. Also discuss its significance in respect of the

formation of heavier elements.

01 Feb 2018

Answer :

Word Count : 560

At a temperature above $10^8 K$ two alpha particles (Helium nuclei) fuse to form a $^{8}Be$ nucleus. This Be nuclei is very unstable and almost decays back to two $^{4}He$ in $2.6 \times 10^{-16}$ seconds. However high density and temperature of the core can cause another $^{4}He$ to strike the $^{8}Be$ (before it decays) resulting in the formation of $^{12}C$ nucleus and emitting two gamma photons.

$^{4}He + ^{4}He \longleftrightarrow ^{8}Be$

$^{8}Be + ^{4}He \longrightarrow ^{12}C + 2 \gamma$

Since in this reaction three alpha particles get converted to one $^{12}C$ it is called the triple alpha process. The production of carbon thus requires the almost simultaneous collision of three particles. The reaction is often written as,

$3 ^{4}He \longrightarrow ^{12}C + \gamma$

Once He burning has been completed at higher temperatures other reactions become possible

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