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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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