Physics

Overview of Radioactive Decay from Heavy Atoms



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In this article I will discuss two radioactive decays from radioactive atoms such as Uranium238.  In addition I will discuss two important nuclear reactions that are mediated by the nuclear weak force.  The nucleus of atoms is usually a stable entity that is able to survive without disintegration for a long period of time.  This rule is valid for most elements of the periodic table except for the group of atoms that is called the actinides.


The nucleus of atoms contains protons which are positively charged in that its different number in the nucleus means the existence of different atoms.  In addition to protons, there are also other particles in the nucleus which are called neutrons.  These are neutral particles in that their number in the nucleus does not affect the identity of the atom but will determine the type of isotope of a certain atom.  Isotopes are atoms of the same type except for they have a different number of neutrons in the nucleus. 


The first type of radioactive decay that is discussed here is the alpha particles decay.  Alpha particles are ionized helium atoms that are positively charged.  Usually radioactive decay from light atoms is not possible due to the extra-stability of their nuclei.  This is so due to the relatively low number of protons and neutrons in the nucleus. 


In heavy atoms, the large number of protons and neutrons in the nucleus makes the nucleus of these atoms unstable, so that radioactive processes from these atoms become more likely.  This can rid the atom of some of its protons and neutrons making it a relatively more stable atom. 


One of these radioactive processes occurs in the heavy metal Uranium which can undergo alpha particles emission.  The energy barrier that is required for alpha particles to be emitted from the nucleus is exceedingly high so that under normal circumstances it is an impossible process.  However, this process does occur and is observed in many heavy atoms.  The explanation to this phenomenon comes from the theory of quantum mechanics. 


There is, in quantum mechanics, a theory that is called the tunneling effect which shows that there is certain finite probability for a particle inside a box with infinitely high walls to overcome that barrier and be outside the box.  This probability accounts for the fact that protons and neutrons can cross the energy barrier of the nucleus which is manifested as the nuclear strong force.  This force holds the neutrons and protons together inside the nucleus.  The tunneling effect of quantum mechanics can nicely explain the phenomenon of alpha particles decay of heavy radioactive atoms such as uranium.                  


A similar process occurs with beta decay of heavy atoms.  In this case the tunneling effect cannot explain this phenomenon due to the lack of conservation of particles.  Beta decay is obtained from the conversion of a neutron to a proton and an electron in addition to a neutral particle that is called the neutrino.  The theory that can explain this beta decay in heavy atoms relies on the nuclear weak force which can explain why neutrons can be converted to protons and electrons and neutrino particles.  Also protons can be converted to neutrons and positrons in addition to anti-neutrinos which are the antiparticles of the neutrinos. 


Neutrons are usually unstable particles that undergo radioactive decay to give protons and electrons in addition to neutrinos.  Protons are more stable than neutrons and are more difficult to undergo radioactive decay.  Due to its neutral charge neutrons are used in the study of heavy atoms because of its easy ability to penetrate the nucleus.  Protons, on the other hand, are not used in this process due to their positive charge that is repelled by the nucleus.  



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