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[X3M CHEMiSTRY/NUCLEAR/PHYSiCS/TECHNOLOGY]: Mass Defects & Alpha Decay


SiRaLeX
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Question 1: Where do mass defects come from? A Li6 core has a mass of 6.01347706u, now substract the mass of its 3 protons and the mass of its 3 neutrons and you end up with a mass defect of 0.03434u, this in turn equates to 32 MeV (as you can see in the picture). Ignore the formal errors, it should be 0.03434u * 931.494 MeV/u.  :P

 

Question 2: Assume that an alpha decay occurs. An Uranium 238 atom decays to a Thorium 234 atom and emits an alpha particle (positively charged Helium 4 core). What happens to the 2 leftover electrons the Thorium ends up with? I mean, technically the Thorium (atomic number 90) ends up with 92 electrons which the Uranium had. Is the Thorium now negatively charged?  :huh:  Is the Thorium now bound to undergo two ß- (beta minus) decays, but that would turn it back into Uranium?  :S  WTF!  :P  Will the Thorium just explode?  :ranting:

 

defects.jpg.9b06dfac8fe369013006d21347608f8c.jpg

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For the missing mass problem, all nucleons have a "Binding Energy", which is simply the energy needed to glue them together. When considering Mass and Energy are basically the same thing (E = MC2) The Mass defect is simply the binding energy of the Nucleus. This is different for various nuclei (and isotopes).

 

For the Alpha Decay's extra electrons, its likely that while the ion might initially have a 2- charge its most likely that the electrons will just migrate from the Negative ion to the positive alpha particle. (Don't quote me on this, I've never thought about it before)

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