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Forum: Documentation and Examples
Re: Question A question on Unit in example rdecay01 (Clare Huang)
Date: 25 Dec, 2011
From: michel maire <michel maire>

On Thu, 22 Dec 2011 23:14:24 GMT, Clare Huang wrote:
>
> can someone explain why? thanks a lot for your time and help in advance!
>

 I apologize to have answered too quickly : I missed your specific worry !

 The purpose of this piece of code is to illustrate a coherent use of system of
units.

1- We want to compute an Activity per unit of mass.
GetAtomicMass() returns ... atomic mass ! that is 60 for Co60, etc ..
Interpreted as mass of a mole, it is explicitely in grammes. Doing
molMass = GetAtomicNumber()*g/mole convert it in internal unit of mass, which
allows to use it without special caution. (idem, when defining a material, you
write A = 60*g/mole). Then :
 nAtoms_perUnitOfMass = Avogadro/molMass;
 Activity_perUnitOfMass = nAtoms_perUnitOfMass/pTimeMean;

 Activity_perUnitOfMass has dimension Activity/Mass and can be printed, for
 example, in becquerel/kg

2- I admit that this construction is somewhat pedantic, and could be simplified as
  nAtoms_perGram = Avogadro/GetAtomicNumber();
  Activity_perGram = nAtoms_perGram/pTimeMean;
  G4cout << Activity_perGram/becquerel << " Bq/g" ;

  But keep in mind that, in this way, we compute an activity per gramme only, 
  not an activity per unit of mass. 

   I hope my explanation is clear,   Michel

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1 None: Re: A question on Unit in example rdecay01   (Clare Huang - 25 Dec, 2011)
(_ None: Re: A question on Unit in example rdecay01   (michel maire - 26 Dec, 2011)
(_ None: Re: A question on Unit in example rdecay01   (Clare Huang - 02 Jan, 2012)
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