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Forum: Hadronic Processes
Re: Question 152Eu (Lise-Lotte Andersson)
Date: 28 Feb, 2011
From: L.G. Sarmiento <L.G. Sarmiento>

Dear forum people,

It looks like I pinned down the problem in the simulation and now I come again to ask for your advice.

The situation is the following: Since 152Eu is a calibration source. I programmed the rod that holds the calibration source inside the chamber as something you can include or exclude by means of a DetectorMessenger i.e. you can place it or not via a macro and it was not included by default.

Since the only 'controversial' part of the code was precisely the placement or not of the rod, I decided to change that and hard coded the "rod" (remember: not present by default) and it turns out that it makes a lot of difference.

Please follow the links and you will find the spectra, for the different scenarios, between 500keV and 1500keV (same range shown by Lisa for the simulation AND the experiment), and please pay special attention to the intensities of the peaks located at ~780keV, ~960keV and 1400keV.

If you let the source "hanging in the air" without placing the holder(rod) you find this:
-> Never placing the "removing line" in the macro. (rod not present by default)
http://dl.dropbox.com/u/18580197/152Eu_NO_holder.png
-> Removed via Detector Messenger
http://dl.dropbox.com/u/18580197/152Eu_macro_NO_holder.png
(they are exactly the same between them since the rod was never there BUT the geometry gets recomputed anyway, details below).

If on the other hand you place the holder via the macro you get this:
http://dl.dropbox.com/u/18580197/152Eu_macro_holder_2.png
(you may notice that this is nothing but the original problem)

BUT, on the other hand if you hard-code the rode from the beggining (holder_flag set to true in the details below), this is what you get:
http://dl.dropbox.com/u/18580197/152Eu_coded_holder.png
(and this is the desired result !!!!)

So, wrapping up: the problem comes to the fact that there is something wrong in the way I include the rod and here comes the part where I want to learn how to avoid fix the situation properly.

The relevant parts of the code are the following:

G4LogicalVolume DetectorConstruction::Construct()
{
...
if(holder_flag) ConstructSampleHolder(); //holder_flag=false by default
...
}

void DetectorConstruction::ConstructSampleHolder()
{
...
... PhysicalVolume definition and placement of the rod inside the chamber
...
}

The relevant part from the DetectorMessenger is this:

if ( command == sampleHolderCmd )
{
 G4bool flag = sampleHolderCmd->GetNewBoolValue(newValue);
 detector->setHolder_flag(flag);
 detector->UpdateGeometry(); //Should I implement a RemoveDaughterVolume function?
}

And this is what the UpdateGeometry() method does:

void DetectorConstruction::UpdateGeometry()
{
  // Cleanup old geometry
  G4GeometryManager::GetInstance()->OpenGeometry();
  G4PhysicalVolumeStore::GetInstance()->Clean();
  G4LogicalVolumeStore::GetInstance()->Clean();
  G4SolidStore::GetInstance()->Clean();
  G4RunManager::GetRunManager()-> GeometryHasBeenModified();
  G4RunManager::GetRunManager()->DefineWorldVolume(Construct());
}


What am I doing wrong here? The volume looks ok in the heprep visualization(!).

Many thanks for the time you spent helping me/us and I apologize if this is not the right forum to ask this follow-up question.


/Pico

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