MadSci Network: Physics

Re: Debate: An infinite amount of energy is needed to make an electrron.

Date: Fri Nov 20 12:22:55 1998
Posted By: Tye Morancy, Grad student, Physics, UMASS Lowell
Area of science: Physics
ID: 910380417.Ph

    Well, you posed your question in an interesting way.  I believe 
another scientist originally attempted to answer your question, since you 
referred to a previous question where clarification was required.  With 
the information you supplied to me, I see a very clear answer.

    One of my backgrounds is in nuclear physics and radiation sciences and 
one of the simplest ways to produce an electron is through a process which 
is called "Pair Production".  If this term is new to you, I will explain.  
Pair production is a process by which a photon creates an electron and a 
positron.  So this process will yield both an electron and positively 
charged electron called the positron.  The energy of the photon going into 
the interaction is equal to the sum of the two rest masses of the 
particles (E=MC^2) and the energies of both.  This process requires the 
presence of a massive atom for the purpose of momentum conservation.  The 
recoil energy of this massive atom is negligible compared to the terms of 
the above equation.  Since we require a minimum of 2mc^2 for the products, 
we thus have the threshold energy required for this process wjich is 1.022 
   Practically speaking, we could perform this process by using an 
accelerator and focusing a highly collimated beam of monoenergetic photons 
on a given slab of material.  Pair production is a process which becomes 
dominant over the other processes of interaction such as compton 
scattering and the photoelectric effect at energies in excess of 5 MeV.  
The downside of this method for producing an electron is that we have 
essentially formed a pair made up of an electron and a positron which can 
interact to form positronium, which after an extremely short lifetime, 
annihilates and two photons are created, which move in opposite direction 
to each other.
   I apologize that this probably did not reach you in time, but I 
answered it as soon as I was able.  If you need further information you 
need only consult the subject of pair production, positronium, or pair 
annihilation.  I hope this answered your question and if clarification is 
still needed just write us back and we will try to get you the answer you 

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