Re: Properties with units (ABSLENGTH)

On 05/04/2012 04:25 PM, Brett Viren wrote:
> I see. Some questions:
>
> Are the VMC units documented somewhere? If not, can you please add
> something to:
>
> http://root.cern.ch/drupal/content/vmc

I have put this on my to do list.

>
> Can VMC get something equivalent to CLHEP's SystemOfUnits.h? Developers
> can then explicitly give units to literal values (eg, "100*meter",
> "3*eV") and not need to care what VMC's unit convention is.

The VMC is in place since ten years and there is a number of applications using already fixed units. So a question is whether it is worth to put this effort now.
Also as VMC is directly using the other Root packages (geometry, particles) which are also using fixed units. So then to be consistent everywhere, the units should be better to be defined in lower level to be usable with the other packages as well.

>
> Does user code need to provide implementation-specific calls to
> SetMaterialProperty() in order to set implementation-specific property
> names? Ie, does the G3 VMC know what the string "ABSLENGTH" means?

Each MC can do only physics which is implemented in their models; the SetMaterialProperty() interface was added in order to allow to use new Geant4 optical physics from VMC, but as this physics does not exist in Geant3, the setting of these parameters will have no effect. (You will be informed about this by a warning issued from TGeant3 when this setting is called.)

Best regards,

Ivana

>
> Regards,
> -Brett.
>
> Ivana Hrivnacova<Ivana.Hrivnacova_at_cern.ch> writes:
>
>> Hi Brett,
>>
>> The VMC is using fixed units as Geant3 (length in cm, energy in GeV,
>> see all in TG4G4Units class).
>> That's why all lengths defined via VMC are interpreted as length in cm
>> and in Geant4 you get the factor of 10, as the "default" length unit
>> (=1) in G4 is mm.
>> The interface function SetMaterialProperty() is quite generic and so
>> the length as RAYLEIGH or WLSABSLENGTH escaped from a control.
>> I will check with Geant4 experts if there is available a list of all
>> material properties which can be defined so that we are sure that
>> there is nothing else forgotten.
>> Thank you for spotting this.
>>
>> Best regards,
>>
>> Ivana
>>
>>
>> On 05/03/2012 11:00 PM, Brett Viren wrote:
>>> Hi again,
>>>
>>> How are property units supposed to be treated in VMC?
>>>
>>> I got a bit of a surprise when I tried to define the ABSLENGTH property
>>> for a material. I was defining the lengths w/in CLHEP'S SystemOfUnits.
>>> When I asked G4 to dump what it received the lengths had all gained an
>>> extra factor of 10.
>>>
>>> I'm setting the property via gMC->SetMaterialProperty() and I found this
>>> code in the definition of that method:
>>>
>>> if ( G4String(propertyName) == "ABSLENGTH" ||
>>> G4String(propertyName) == "MIEHG" )
>>> val2[i] = val2[i]*TG4G3Units::Length();
>>>
>>> Other lengths such as RAYLEIGH or WLSABSLENGTH seem to pass unmolested
>>> into G4.
>>>
>>> -Brett.

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