October 16, 2016 Sunday

Bedtime Story


The CNO Fusion Cycle

The chain reaction that Bethe and Charles Critchfield had worked out one year after the 1938 Washington conference is known as the CNO cycle or the carbon-nitrogen-oxygen cycle.

There are fundamental differences between these two chain reactions of proton-proton and CNO.

The proton-proton chain reaction is a temperature dependent reaction starting at a relatively lower temperature of around 4 X 10⁶ K.

This high temperature or high kinetic energy is required for proton to overcome the strong Coulomb repulsion between their nuclei.

Even when 2 protons do manage to combine and form diprotons (Helium-2 or 2 protons with no neutrons), they tend to immediately decay back to 2 protons.

The conversion of hydrogen to helium is extremely slow, so slow that even at the core of the sun it would take 10¹⁰ years for all hydrogen to be converted to helium.

The CNO cycle on the other hand is a catalytic reaction where in isotopes of carbon, nitrogen and oxygen act as catalysts in the fusion of 4 protons to form 1 alpha particle, 2 positrons and 2 electron neutrinos.

12 6C	+	p	→	13 7N	+	γ
13 7N			→	13 6C	+	e+	+	ν e
13 6C	+	p	→	14 7N	+	γ
14 7N	+	p	→	15 8O	+	γ
15 8O			→	15 7N	+	e+	+	ν e
15 7N	+	p	→	12 6C	+	4 2He

Energy is released in the form of gamma rays when electrons with positrons and annihilate each other.

One of the protons will end up becoming isotopes of carbon, nitrogen and oxygen in endless loops.

As compared to proton-proton chain, the CNO cycle needs far higher temperature to begin with (15 X 10⁶ K), but once initiated it becomes self enforcing being both exothermic and catalytic.

So it is a self sustaining chain reaction cycle fueling itself with its own products.

       

Bethe never forgot his mother trapped in Nazi Germany who became increasingly fearful of her life, particularly following the November 9-10, 1938 pogrom against the Jews.

That fearful night is infamously known as the Night of the Broken Glass or to the natives Kristallnacht.

Stay tuned to the voice of an average story storytelling chimpanzee or login at http://panarrans.blogspot.in/

Good night and my fellow cousin ape.

Another great educator and a teacher that I am aware of is Professor Subhashish Chattopadhyay in Bangalore, India.

While I narrate stories, Professor Subhashish an IIT graduate and a teacher at BARC, does and teaches real mathematics and physics.

He started the participation of Indian students at the International Physics Olympiad.

Do visit him here:

http://skmclasses.weebly.com/

All his books can be downloaded for free through this link:

https://zookeepersblog.wordpress.com/science-tuition-chemistry-physics-mathematics-for-iit-jee-aieee-std-11-12-pu-isc-cbse/

For entertainment and English education of your children, may I suggest this large collection of Kids Songs:

https://www.youtube.com/channel/UCMX11Z5SJQ3kgwSsFJLRIcg