# How can I add material having areal density (gm/cm2) in G4Material?

I want to construct a material in GEANT4, having its areal density (thickness) given in gm/cm2 provided in this paper.

Here, a cylindrical slab of aluminum of 10 or 20 gm/cm2 and water of 30 gm/cm2 structure, which I want to create in GEANT4 (page no. 4 (structure)). units are given in gm/cm2.

I am a beginner and since the G4Material class has a density in gm/cm3, as shown,

From definition:-

density = 2.700g/cm3;
a = 26.98
g/mole;
G4Material* Al = new G4Material(name=“Aluminum”, z=13., a, density);

Here, density is taken in gm/cm3, how such I proceed further?

Is there any way to convert areal density to volume density? or, Is there is a specific command? Please guide me.

divide areal density by volume density to get the thickness of the slab. then you can define the different geometries, and specify the volume density like the code snipped you posted.

different areal density implies different thickness “below the surface”, i.e. a different geometry

Thank you @weller. this idea works but it does not give any information on the other 2 length parameters of Aluminum material (3D). Can you please suggest something?

i would suggest to make it „large enough“, assuming you will probably just shoot with a pencil beam of particles and measure transmission or something? maybe 10 times the thickness is sufficient?