sPHENIX HCal discussion

[John Lajoie <lajoie AT iastate.edu>]

Hi Ed, John:

    It will probably be sufficient to just have a look at the properties of the material mixtures in GEANT, including the proper mixture of 310 stainless, but given what John has found I would bet they are almost identical.

Regards,
John

On 6/19/2015 6:21 PM, EdwardOBrien wrote:

	John,
	 Your analysis seems quite reasonable. Then you're proposing
	that we use standard steel for the performance prototypes
	for both the Inner and Outer. The mechanical or engineering
	prototypes are to be made of the actual material we intend to
	use. Do you think that it is worthwhile adding a GEANT4
	performance study of a 310 stainless vs standard steel
	calorimeter to our list of detector simulations. I am sure
	that a committee will ask.

	Ed


On 6/19/2015 11:41 AM, John Haggerty wrote:

The question of whether we need to make the IHCAL performance prototype
out of stainless steel came up at yesterday's meeting again.  It's
harder to work with mechanically, and more expensive, and I don't think
there will be any discernible difference, and here's my analysis of that
question.  Of course, I could be wrong, so more eyes on the question
would be good.

The non-magnetic stainless steel we used in the PHENIX absorber on the
central magnet came with an assay that had these components:

     Z       A     rho       X       %
C    6  12.011   2.266  42.698   0.050
Mn  25  54.938   7.473  14.640   0.960
P   15  30.974   1.820  21.205   0.025
S   16  32.060   2.086  19.493   0.000
Si  14  28.086   2.329  21.823   0.560
Ni  28  58.700   8.907  12.679  19.380
Cr  24  51.996   7.194  14.944  24.450
Mo  42  95.940  10.222   9.801   0.250
Co  27  58.993   8.800  13.631   0.150
Cu  29  63.546   8.933  12.862   0.280
N    7  14.007   0.001  37.989   0.055
Fe  26  55.847   7.873  13.839  53.840
                 7.874  13.873

and if you cruise the web, you'll see that's typical for "310 stainless
steel."  (The above table was from when we got it and I calculated the
radiation length of the mixture for fun; if I did the weighting right,
the radiation length of the SS310, the 13.873 g/cm^2, is pretty close to
elemental Fe, which is >99.5% of a carbon steel like 1006 which we'll
use in the flux return; the density is pretty much the same, too.)  It's
not mysterious, the other big components, Ni and Cr, surround Fe on the
periodic table, and have quite similar properties.

I thought I better check a little further, so I used my super-idealized
model of the IHCAL based on a GEANT example to look at the difference; I
made a nominal 1 interaction length calorimeter out of 4 Fe plates
(that's the "4 crossing") 42 mm thick (the interaction length of Fe is
167.7 mm), and shot some 10GeV pi+'s at it and used matScan to measure
the interaction length.

The calorimeter is 4 layers of: [ 42mm of G4_Fe + 7mm of G4_POLYSTYRENE ]
 mean Energy in Absorber : 1.74625 GeV +- 1.86963 GeV
 mean Energy in Gap      : 56.5529 MeV +- 61.824 MeV
 mean trackLength in Absorber : 1.1057 m   +- 1.19615 m
 mean trackLength in Gap      : 19.1849 cm  +- 19.3933 cm

and the matScan agrees with my arithmetic:


/control/matScan/singleMeasure 0 0

         Theta(deg)    Phi(deg)  Length(mm)          x0     lambda0
                  0           0      1017.6     9.62684     1.03024

The material G4_STAINLESS-STEEL packaged with GEANT isn't 310, it's
about 74% Fe, so we should cook up the material correctly, but just to
get a quick idea, here are the statistics from running 10 GeV pions
through that, and the matScan:

The calorimeter is 4 layers of: [ 42mm of G4_STAINLESS-STEEL + 7mm of
G4_POLYSTYRENE ]
 mean Energy in Absorber : 1.7336 GeV +- 1.76738 GeV
 mean Energy in Gap      : 59.5918 MeV +- 65.2185 MeV
 mean trackLength in Absorber : 1.03557 m   +- 1.08142 m
 mean trackLength in Gap      : 18.3985 cm  +- 18.4141 cm

         Theta(deg)    Phi(deg)  Length(mm)          x0     lambda0
                  0           0      1017.6     9.73369     1.04876

So I think it's ok to make the prototype out of pretty much any steel as
far as its properties as an absorber, as far as I can see.  Probably not
so true for the mechanical prototype, where we may have to learn to deal
with a material that is rather difficult to work with.



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John Lajoie

PHENIX Deputy Spokesperson

Professor of Physics

Iowa State University

 

(515) 294-6952

lajoie AT iastate.edu

Contact me: john.lajoie