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when an alpha particle hit berrelyium it emits neutron. Does the alpha particle causes unstability to the nucleus or any other reason?

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closed as off-topic by Mithoron, aventurin, airhuff, Tyberius, Avnish Kabaj May 26 '18 at 10:18

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    $\begingroup$ Alpha particle is itself a nucleus, just a relatively little one. Then again, beryllium is not awfully large either. Imagine a head-on collision of Earth and Mars; I have a vague feeling you wouldn't want to describe it in terms like "Mars causes instability to Earth". $\endgroup$ – Ivan Neretin May 22 '18 at 7:23
  • $\begingroup$ So then it is due to the kinetic energy of the alpha particles. Is this true? $\endgroup$ – khankk May 22 '18 at 8:37
  • $\begingroup$ Yes, you may put it this way. $\endgroup$ – Ivan Neretin May 22 '18 at 9:01
  • $\begingroup$ I disagree with @IvanNeretin's comment. This is a quite well known nuclear reaction, 9Be($\alpha$,n)12C (amongst other things well known as the neutron spark plug for the first atomic bomb). The 13C intermediate nucleus that is formed is some 10MeV above the ground state. One relaxation path is through releasing a neutron to leave 12C. (Remember that you need to conserve both energy and momentum in the center-of-mass frame of the interaction.) The overall Q value for this reaction is about 5MeV. $\endgroup$ – Jon Custer May 22 '18 at 13:30
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The reaction can be regarded as a fusion reaction, the fast moving helium nucleous has sufficent energy to overcome the electrostatic repulsion of the positvely charged beyllium nuclous. What happens is that the alpha particle will enter the berylium nucleous to form the product.

The product will be carbon 13 in an excited state, the carbon 13 could relax down to the ground state by the emission of gamma rays (photons) but by the ejection of a neutron it is able to convert itself into the very stable carbon-12.

In the same way as in chemistry we have the chemcially very stable noble gases (full electron shells) in nuclear science we have some nuclides which are blessed with additional stability.

Carbon-12 has both an even number of protons and neutrons which will increase its stability more than a odd,odd, even,odd or odd,even nuclide. Also there are some magic numbers which correspond to complete shells of nucleons (protons and neutrons). Carbon-12 is not one of these magic nuclides (full shells of protons and/or neutrons) but it is more stable than carbon-13.

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