Using Mass number instead of Atomic Number

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Although the mass number is useful for determining whether the atoms are 
isotopes of the specified element, it is not an accessible piece of 
information. We should go back to atomic number. This will change things in at 
least the following files:
* AtomClass
* readfiles
* csection_calc
* GUI_Main

Original issue reported on code.google.com by wfly...@gmail.com on 4 Aug 2010 at 5:22

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I guess you and William discussed this?  I thought it was/would be necessary 
for a calculation.

Original comment by tsar...@gmail.com on 4 Aug 2010 at 7:48

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[deleted comment]

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Also, it's a bit redundant to ask for atomic number and symbol.  It could be 
removed entirely.

Original comment by tsar...@gmail.com on 4 Aug 2010 at 7:50

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Yeah, he figured no one would know the mass of the elements they were working 
with off the tops of their heads. 

Maybe we can have a Symbol text-field and then where atomic/mass number is, we 
can have a drop down menu for the isotopes that is updated for the element in 
the Symbol field. So if you have Fe in Symbol, you would maybe see a drop down 
menu that has:
Fe56 }
Fe54 }naturally occurring sorted by abundance or something
Fe57 }
Fe58 }
Fe60 ]synthetics
Fe59 ]
This might be too complicated for now and we can just have symbol. Valence is 
still important though.

Original comment by wfly...@gmail.com on 4 Aug 2010 at 8:05

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I made the field optional, so the user can leave it blank, or if they happen to 
know their isotope, they can enter a valid isotope number.

Original comment by tsar...@gmail.com on 28 Jan 2011 at 10:04

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Original comment by tsar...@gmail.com on 28 Jan 2011 at 10:08

• Changed state: Fixed