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Author Topic: What causes this discrepancy in beta decay energy?  (Read 1965 times)

Offline ghh

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I have been looking at beta decay chains and I have noticed a curious discrepancy between beta minus and beta plus.
In the table I have converted decay energy in keV to AMU for convenience.
DE is decay energy; MD is mass difference
For Beta minus, the decay energy is almost the same as the mass difference between parent and daughter isotope.
For Beta plus there is a difference of about 1022Kev. (about 2 electron masses)
This example is Atomic Number 65, but itís a consistent effect for every beta decay chain.
Does anyone know why?
Nuclide     DE             MD           DE - MD      DE - MD (keV)
65V   0.017760   0.017760   -0.0000004   -0.33684
65Cr   0.013824   0.013820   0.0000040   3.75028
65Mn   0.010956   0.010960   -0.0000045   -4.17634
65Fe   0.008902   0.008902   -0.0000002   -0.16129
65Co   0.006394   0.006394   0.0000004   0.40559
65Ni   0.002295   0.002295   0.0000000   0.01713
65Cu   STABLE         
65Zn   0.000354   0.001452   -0.0010974   -1022.2
65Ga   0.002396   0.003494   -0.0010974   -1022.23
65Ge   0.005604   0.006705   -0.0011013   -1025.85
65As   0.009031   0.010120   -0.0010893   -1014.72
65Se   0.013999   0.015100   -0.0011010   -1025.56

« Last Edit: 22/05/2008 22:13:25 by chris »


 

Offline Soul Surfer

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What causes this discrepancy in beta decay energy?
« Reply #1 on: 20/06/2008 19:57:42 »
The reason for this is fairly obvious if you think about it.  Electron emitters effectively have an excess of neutrons and a neutron can decay into a proton and emit an electron. Now in atoms that are seriously short of neutrons the converse cannot happen because protons are stable. however it is possible for an electron positron pair to come out of the vacuum woth some energy excess and for a proton to be converted into a neutron by the elctrons combining with it leaving the positron to escape from the nucleus so there is an extra energy deficit of an electron pair to be considered in the process as you have noted.
 

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What causes this discrepancy in beta decay energy?
« Reply #1 on: 20/06/2008 19:57:42 »

 

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