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Beta minus decay

  1. Oct 10, 2014 #1
    1. The problem statement, all variables and given/known data
    in the first photo of my note , it says that the product nucleus has Z electrons (not Z+1) electrons ,
    whereas for the 2nd part of my note , it says that the atomic masses of the product nucleus( which has A nucelon mumber and Z+1 proton number) , it has one extra orbitting electrons

    why the 2nd part of the note is different from the first one? the product nucleus has Z+1 electrons or Z electrons?
    2. Relevant equations

    3. The attempt at a solution

    Attached Files:

  2. jcsd
  3. Oct 11, 2014 #2


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    I think they're trying to say the same thing, but the second is very poorly worded. The notation contributes to the problem.
    ##^A_{Z+1}Y## in the equation they both quote represents an ion, i.e. It is missing an electron. How are you supposed to know this from the notation? Shouldn't it be something like ##^A_{Z+1}Y^+##?
    The first text treats it as representing an ion throughout. The second text seems to recognise the ambiguity; the references after the equation interpret it as the un-ionised atom, so needs to subtract off the mass of the electron when calculating the mass loss. I.e., ##m_y## is the mass of the un-ionised atom.
  4. Oct 11, 2014 #3
    ##^A_{Z+1}Y## represent positive ion am i right? but not ##^A_{Z+1}Y^+## ... the product nuclei has Z+1 proton but the number of electrons remained the same.... so for ##^A_{Z+1}Y## , it's a positive ion... am i right?

    i knew this from the first photo.
  5. Oct 11, 2014 #4


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    Forget about the beta decay for the moment. Y represents some element. The notation ##^A_{Z+1}Y## should represent an atom of element Y, having atomic mass A and Z+1 protons. In the absence of any indication as to whether it is ionised, one would assume it therefore has Z+1 electrons. The right hand side of the equation should therefore read ##^A_{Z+1}Y^++e^-##.
    Anyway, do you now understand that the two texts are trying to say the same thing?
  6. Oct 11, 2014 #5
    alright, can you please look at the 2nd photo?
    i can understand why the mass defect (for atomic mass) is mx -( my-me) -me , why not mx -( my+me) -me ?

    before subtracting the mass of the 'extra orbitting electron' , why the mass defect is calculated by mx-my-me (just like nuclear mass at the top part ) ??
  7. Oct 11, 2014 #6


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    As I wrote, that text is taking my to be the mass of a 'complete' (un-ionised) atom of Y. Since it is ionised (+), its mass is my-me. The wording in the text is atrocious, and I'm not surprised you are confused. Is it a translation?
  8. Oct 11, 2014 #7
    i will try my best to understand . i am not sure whether it's the translation or not. but i english is not my first languange...
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