# Beta minus decay

1. Oct 10, 2014

### gxc9800

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

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2. Oct 11, 2014

### haruspex

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.

3. Oct 11, 2014

### gxc9800

$^A_{Z+1}Y$ 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.

4. Oct 11, 2014

### haruspex

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?

5. Oct 11, 2014

### gxc9800

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 ) ??

6. Oct 11, 2014

### haruspex

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?

7. Oct 11, 2014

### gxc9800

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...