Defining the material Thallium Activated Sodium Iodide

Geometry, Fields and Transportation
1

Hi, regarding the construction of my detector I have defined the material Thallium Activated Sodium Iodide (NaI(Tl)), I have done this in 3 different ways/methods. Are the 3 ways/methods correct, or which is the correct one?. How should I define this material?. Below I show the code of the three methods/ways to define this material:

void myDetectorConstruction::DefineMaterials()
{

///////// First method
G4NistManager* man = G4NistManager::Instance();

G4bool isotopes = false;

G4Element* Tl = man->FindOrBuildElement(“Tl” , isotopes);
G4Element* I = man->FindOrBuildElement(“I”, isotopes);
G4Element* Na = man->FindOrBuildElement(“Na”, isotopes);

auto NIT = new G4Material(“NaITl”, 3.67 * g / cm3, 3);
NIT->AddElement(Na, 1);
NIT->AddElement(I, 1);
NIT->AddElement(Tl , 1);
////////////////////////////////////////////////////////////////////////////////////////////
////////// Second method
G4Element* elTl = new G4Element(“Thallium”,symbol=“Tl”,z=81.,a=204.3833g/mole);
G4Element elI = new G4Element(“Iodine”,symbol=“I”,z=53.,a=126.90447g/mole);
G4Element elNa = new G4Element(“Sodium”,symbol=“Na”,z=11.,a=22.989769*g/mole);

G4Material* NaITl = new G4Material(“Iodide”,density=3.67 * g / cm3,ncomp=3);

Iodide->AddElement(elI, natoms=1);
Iodide->AddElement(elNa, natoms=1);
Iodide->AddElement(elTl, natoms=1);

////////////// Third method

G4Element* elTl = new G4Element(“Thallium”,symbol=“Tl”,z=81.,a=204.3833*g/mole);
auto elI = new G4Element(“Iodine”, “I”, z = 53, a = 126.90447 * g / mole);
auto elNa = new G4Element(“Sodium”, “Na”, z = 11, a = 22.989769 * g / mole);

auto Iodide = new G4Material(“Iodide”, density = 3.67 * g / cm3, nelements = 3);

Iodide->AddElement(I, 45. * perCent);
Iodide->AddElement(Na, 45. * perCent);
Iodide->AddElement(Tl, 10. * perCent);
////////////////////////////////////////////////////////////////////////////////////////////
////////////////////////////////////////////////////////////////////////////////////////////

}

_Geant4 Version:_11.2.1
_Operating System:_Windows 10
_Compiler/Version:_Visual Studio 2022
_CMake Version:_3.29.0-rc2

2

The 3 codes seem correct ( z must be an integer).
Methodes 1 and 2 are equivalent. You define a molecule of NaITl : 1 atome of each
Methode 3 defines a mixture of (Iodine,Sodium,Thallium), with( in mass) 45% I, 45% Na, 10% Tl

3

Ok, thank you very much for answering. So I think that what I am going to use will be method 1 or method 2, because method 3 is a mixture, and in a mixture the order in which one mixes the materials doesn’t matter, right?

4

All methods must be independent of the order ! if not, there is a bug somewhere …

In your DetectorConstruction, add something like : G4cout << " \n " << NaITl << G4endl;

5

Ok, thanks. I’ll try to do that

6

Is there an example from the Geant4 toolkit where something similar to: G4cout << " \n " << NaITl (or other material) << G4endl; is done?.

7

In hadronic/Hadr03 : DetectorConstruction::PrintParameters()

And also Hadr04, Hadr05 …etc…

8

Ok, thanks for the information. I’ll take a look at those examples.

9

I may be wrong, but please check the amount of thallium in NaI(Tl). Usually, it is 500-1500 ppm.

10

Ok, thanks for the information. I didn’t know that information. I’ll take a look at the NaI(Tl) data

11

Hi Philipp, sorry for my late response; I checked the manufacturer’s data sheet, but I couldn’t find the amount of Thallium in Sodium Iodide. I think I’m going to have to look up that information in books.

12

You generally will not find the Tl doping concentration quoted in the manufacturers’ data sheets. The doping varies from detector to detector. However, a typical example that I found is 1.3x10^-3 mole fraction quoted in J.N.Mundy and S.J. Rothman, Methods in Experimental Physics, Elsevier, 1983.

It is worth noting that the concentratiion is sufficiently small that it can usually be ignored if you are only looking at energy deposited in the scintillator. If you are using the optical physics package for the scintillation process, you do not need the concentration. You just need the optical properties of the scintillator, which the manufacturer should have, even if they do not quote the Tl concentration.

1 Like
13

Ok John, thank you very much for your reply. I will keep this in mind. I have a question, is the energy deposited equivalent to the counts (counts shown for example in a spectrum of counts versus channel), right?

14

They will be similar, but the energy deposited spectrum will have peaks, Compton edges, etc. with perfect energy resolution. Speaking very broadly, It will look somewhat like an idealized version of an actual ‘counts’ spectrum. Energy broadening, nonlinearities and losses due to the scintillation and optical transport process will be absent.

15

Ok, thanks. I will keep this in mind