[Halld-offline] [EXTERNAL] Re: Question concerning one material definition in hdgeant

[Eugene Chudakov]

Hi Richard,

Thanks. According to the 2020 CDC paper, the radiation length of the 6mm-thick end plate is 2.14%. So, the RadL of the material should be 28cm, slightly longer than 24cm in your second example.
Here, I suppose that 2.14% is the thickness along the plate's material. About 70% of the plate's surface is holes for the straws, effectively filled with the straws' end plugs.

Eugene
________________________________
From: Richard T. Jones <richard.t.jones at uconn.edu>
Sent: Thursday, March 26, 2026 2:59 PM
To: Eugene Chudakov <gen at jlab.org>
Cc: Simon Taylor <staylor at jlab.org>; HallD Software Group <HallD-Offline at jlab.org>
Subject: [EXTERNAL] Re: Question concerning one material definition in hdgeant

Eugene,

Yes it is strange. Looking back through the logs, I see that this material CarbonFiberEpoxy was introduced by me back in May, 2007, and it had this redundant CarbonFiber component from the start. With this apparent duplication of the carbon fiber component, here is what the material description looks like in G4:

Idle> /material/g4/printMaterial CarbonFiberEpoxy
 Material: CarbonFiberEpoxy    density:  1.910 g/cm3   RadL:  22.245 cm   Nucl.Int.Length:  41.172 cm
                       Imean:  77.577 eV   temperature: 293.15 K  pressure:   1.00 atm

   --->  Element: Carbon (C)   Z =  6.0   N =    12   A = 12.011 g/mole
         --->  Isotope:   C12   Z =  6   N =  12   A =  12.00 g/mole   abundance: 98.930 %
         --->  Isotope:   C13   Z =  6   N =  13   A =  13.00 g/mole   abundance:  1.070 %
          ElmMassFraction:  94.01 %  ElmAbundance  79.47 %

   --->  Element: Hydrogen (H)   Z =  1.0   N =     1   A =  1.008 g/mole
         --->  Isotope:    H1   Z =  1   N =   1   A =   1.01 g/mole   abundance: 99.989 %
         --->  Isotope:    H2   Z =  1   N =   2   A =   2.01 g/mole   abundance:  0.011 %
          ElmMassFraction:   1.77 %  ElmAbundance  17.85 %

   --->  Element: Oxygen (O)   Z =  8.0   N =    16   A = 15.999 g/mole
         --->  Isotope:   O16   Z =  8   N =  16   A =  15.99 g/mole   abundance: 99.757 %
         --->  Isotope:   O17   Z =  8   N =  17   A =  17.00 g/mole   abundance:  0.038 %
         --->  Isotope:   O18   Z =  8   N =  18   A =  18.00 g/mole   abundance:  0.205 %
          ElmMassFraction:   4.22 %  ElmAbundance   2.68 %

Here is what it produces if I remove the redundant CarbonFiber entry:

Idle> /material/g4/printMaterial CarbonFiberEpoxy
 Material: CarbonFiberEpoxy    density:  1.746 g/cm3   RadL:  24.266 cm   Nucl.Int.Length:  44.540 cm
                       Imean:  75.646 eV   temperature: 293.15 K  pressure:   1.00 atm

   --->  Element: Carbon (C)   Z =  6.0   N =    12   A = 12.011 g/mole
         --->  Isotope:   C12   Z =  6   N =  12   A =  12.00 g/mole   abundance: 98.930 %
         --->  Isotope:   C13   Z =  6   N =  13   A =  13.00 g/mole   abundance:  1.070 %
          ElmMassFraction:  90.41 %  ElmAbundance  69.94 %

   --->  Element: Hydrogen (H)   Z =  1.0   N =     1   A =  1.008 g/mole
         --->  Isotope:    H1   Z =  1   N =   1   A =   1.01 g/mole   abundance: 99.989 %
         --->  Isotope:    H2   Z =  1   N =   2   A =   2.01 g/mole   abundance:  0.011 %
          ElmMassFraction:   2.84 %  ElmAbundance  26.14 %

   --->  Element: Oxygen (O)   Z =  8.0   N =    16   A = 15.999 g/mole
         --->  Isotope:   O16   Z =  8   N =  16   A =  15.99 g/mole   abundance: 99.757 %
         --->  Isotope:   O17   Z =  8   N =  17   A =  17.00 g/mole   abundance:  0.038 %
         --->  Isotope:   O18   Z =  8   N =  18   A =  18.00 g/mole   abundance:  0.205 %
          ElmMassFraction:   6.75 %  ElmAbundance   3.92 %

Idle>

So it seems like the duplicate entry increases the absorption by about 10%, which may be significant for some reactions. That does not mean either one is correct in terms of the description of the actual downstream endpolate. All of these properties should be reviewed, and some may need updating.

-Richard Jones

On Thu, Mar 26, 2026 at 10:51 AM Eugene Chudakov <gen at jlab.org<mailto:gen at jlab.org>> wrote:

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Hi Richard,

For the CDC endplate a material definition in  Material_HDDS.xml is:

 <composite name="CarbonFiberEpoxy">
        <addmaterial material="CarbonFiber">
                <fractionmass   fraction="0.60" />
        </addmaterial>
        <addmaterial material="EpoxyResin">
                <fractionmass   fraction="0.40" />
        </addmaterial>
        <addmaterial material="CarbonFiber">
                <fractionmass   fraction="0.60" />
        </addmaterial>
  </composite>

I asked Simon about the duplication and he found it strange. What mixture does it define?

Thanks,
Eugene

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