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Doubt on Alpha Rays

Alpha rays are helium nuclei since they have two protons and no electrons. They are He 2+ ions. However we have learnt that helium has highest ionization energy  and an extremely large amount of energy is needed for it to form an ion. According to this, it is not possible for a dipositive cation of helium to exist, however it does . What could be the reason?



First of all Alpha particle is not a doubly ionized Helium Atom. It is emitted from the nucleus of a discintegrating atom.

The "curve of binding energy": A gra...


The energy required to peel off the two electrons is not too much as compared to the energy  involved in the alpha particle emission which is a nuclear reaction. Alpha particles are normally emitted as a part of radio active disintegrations, emitted by naturally unstable nuclei or artificially instabilized nuclei.


The ionization energy of helium is discussed in the purview  of the energy required to remove the electrons. Helium is having a stable duplet electronic configuration which makes it a stable atom. But the energy considerations in nuclear reactions are very much different and higher.


The first ionization energy of helium  is 2372.3 kJ/mol and the second ionization energy is 5250.5 kJ/mol


16 MeV = 16×1.6×10-13 J per nucleus 2.56 x 10-12 J per nucleus


which makes of the order of 1010 kJ per mol of Helium. This is evidently a huge amount compared to that of the ionization energy.


Basically there are a number of differences between chemical reactions and nuclear reactions.


1. In chemical reactions the electrons are taking part in reactions whereas in nuclear reactions the nucleons (protons and neutrons) are involved


2. In nuclear reactions the energy involved is very much large as compared to that in chemical reactions


3. The identity of the element dioes not change in chemical reactions whereas the identity is changed in most of the nuclear reactions.



Nuclear Fission and Fusion – A Facebook conversation

Find below a conversation between Master Deepak, PUC student and Mr. Mathew Abraham, Physics teacher.

Deepak asked: “nuclear fusion or fission in which of these energy released is more and why?”


Energy released per fission is more than energy released per fusion. But energy released per unit mass during fusion is very much greater than energy released per unit mass during fission


But why energy released is more


The fission of a U-235 releases about 200 MeV of energy
whereas the fusion of 4H to form He releases only about  20 MeV
But, the 200 MeV is obtained from 236 amu
and the 20 MeV is obtained from just 4 amu


Then why dont we use nuclear fusion as source of energy and electricity



Nuclear fusion requires very high temperature to start. It is difficult to maintain such a huge temperature (of the order of million degrees).

Tokamak magnetic field and plasma current.
Tokamak magnetic field and plasma current. (Photo credit: Wikipedia)

Research is going on to construct nuclear fusion reactor

The international prototype is named tokamak
In that the nuclear fusion is carried out in plasma state held at high temperature confined in magnetic field produced by huge torroidal solenoids


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