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Forum: Geometry
Date: 30 Oct, 2018
From: Michael H. Kelsey <Michael H. Kelsey>

Sergio Losilla writes:
> Hmmm, OK, looking at G4Element.hh in more detail answered my question:
> 
>     134:  // Atomic weight in atomic units
>     135:  inline G4double GetN()             const {return fNeff;}
>     136:  inline G4double GetAtomicMassAmu() const {return fNeff;}
> 
> So G4Element::GetN() returns the atomic weight, and not the average N.
> 
> Is this standard notation? I apologize if this is a silly question, I am
> not a particle or nuclear physicist but a computational physics
> outsider...

Unfortunately, I'm not a chemist, and they're the ones who invented elements
;->  I don't know if it's a standard definition in the literature.  As near
as I can tell, it's in G4 as a convenience, in order to get from a proper
value of atomic mass in real mass units (g/mol) to a dimensionless value,
without having to do two divisions everywhere.

> I mean, at the moment it seems that:
> 
>    A_element = sum_isotope w_isotope * A_isotope
>    N_element = A_element/(g/mol)
> 
> instead of what I expected
> 
>    A_element = sum_isotope w_isotope * A_isotope
>    N_element = sum_isotope w_isotope * N_isotope

Actually, the latter is what might naively have expected as well.  

> My main worry is that I am defining the element wrong, and that a wrong
> value of N is used at some stage of the simulation yielding wrong
> results. But I guess I can proceed safely.

Nope.  I can guarantee that if N=A/(g/mol) is what's in the code, then any
G4 code that _uses_ G4Element::GetN() will be expecting that value, and
changing it would break much more than it "fixed" :-)

      -- Mike

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1 None: Re: What is the correct way to create a G4Element consisting of a single G4Isotope?   (Sergio Losilla - 30 Oct, 2018)
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