Detector response

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moad
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Detector response

Post by moad » Tue Jun 29, 2021 12:56 pm

Hi,

I am working on this design for a neutron detection system that is based on 4 scintillators (with LiF/ZnS material) inside an aluminum cylinder and I am testing the response of the detector by placing it in a water tank with a Cf-252 neutron source at the center (see attached figure), everything works fine but when I try to change the material composition inside D1 by reducing the atomic fraction of Li-6 I get a higher reaction rate from serpent compared to the other 3 scintillators that were left with the original composition, I was expecting to get a lower reaction rate since I reduced the atomic fraction of Li-6, so can you please tell me if I am doing sth wrong? (note: I also tried to change the dimensions of D1 instead of changing the material composition and I made it smaller but I also got a higher reaction rate compared to the other 3 scintillators that were left with the original dimensions)

Here is how I am defining my Lif/ZnS material cards:
mat lif1 -3.365 #inside D2,D3,D4
3006.03c 1
9019.03c 1
30000.03c 1
16000.03c 1
--------------------
mat lif2 -3.365 #inside D1
3006.03c 0.8
9019.03c 1
30000.03c 1
16000.03c 1

And here is how I am defining my detector response cards:
det 1 dr 105 li dm lif2 dc 222 dv 0.009425 #I use dr 105 since I am mainly interested in the (n,t) reaction rate
det 2 dr 105 li dm lif1 dc 333 dv 0.009425
det 3 dr 105 li dm lif1 dc 444 dv 0.009425
det 4 dr 105 li dm lif1 dc 555 dv 0.009425

Thanks in advance,
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Ana Jambrina
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Re: Detector response

Post by Ana Jambrina » Tue Jun 29, 2021 3:29 pm

Positive MT corresponds with microscopic reaction rates, meaning dr 105 li the flux is multiplied by the microscopic (n,t) of material ‘li’ cross section and integrated over space defined by ‘dm’ and ‘dc’ detectors.
- Ana

moad
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Re: Detector response

Post by moad » Tue Jun 29, 2021 7:30 pm

Thanks for your reply Ana, so if I use "dr -55" for example which corresponds to the macroscopic triton production cross section that would solve the problem?

Ana Jambrina
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Re: Detector response

Post by Ana Jambrina » Tue Jun 29, 2021 10:02 pm

How did you defined material ‘li’ ? If you have set the unit densities in the detector material, macroscopic and microscopic cross sections would be equivalent. A change in densities should be reflected in mthe macroscopic reaction rates.

The reaction number -55 gives you the macroscopic rate and 205 the microscopic rate. If you multiply the microscopic reaction rate estimate from the detector 1 with the atomic density of ‘li’ in ‘lif2’ material, you should get a value that is closer to the macroscopic reaction rate from the analogous detector: [ det 1micro dr 205 li dm lif2 ] * dens[ lif2(li) ] ~ [ det 1macro dr -55 lif2 dm lif2 ].
Last edited by Ana Jambrina on Wed Jul 21, 2021 4:11 pm, edited 1 time in total.
- Ana

tlyytinen
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Re: Detector response

Post by tlyytinen » Wed Jul 21, 2021 3:33 pm

I have also been thinking about microscopic and macroscopic cross section while calculating triton production rate with different compositions of Li6 and Li7. I have produced my triton production results that seem reasonable with macroscopic reaction (-55) but I'm thinking, how could I produce equivalent values with Li6 and Li7 microscopic reactions (205)? The material where I am calculating triton production, the material density is given as mass density and nuclide fractions as mass fractions.

Examples of my definitions:

% --- Total TPR macroscopic detector

det total_TPR n dr -55 blanket_material_m24 dm blanket_material_m24

% Microscopic TPR detectors for Li6 and Li7 reactions

det TPR_micro_Li6 n dr 205 matLi6 dm blanket_material_m24
det TPR_micro_Li7 n dr 205 matLi7 dm blanket_material_m24

% Material definition
mat blanket_material_m24 -8.7319 rgb 0 250 0
% PbLi
82208.03c -4.06655E-01
82207.03c -1.67988E-01
82206.03c -1.89972E-01
3006.03c -4.22301E-03
3007.03c -5.47300E-04
% more...

Ana Jambrina
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Re: Detector response

Post by Ana Jambrina » Wed Jul 21, 2021 4:00 pm

If you multiply the result of 'TPR_micro_Li6' and 'TPR_micro_Li7' with the atomic density of 'matLi6' and 'matLi7', respectively, in 'blanket_material_m24' (assuming those are the sole triton production materials), you should get a value closer to 'total_TPR'.
- Ana

tlyytinen
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Re: Detector response

Post by tlyytinen » Thu Jul 22, 2021 12:21 pm

Thank you Ana for quick response. I had missed that in Serpent atomic density unit is 10^24/cm^3 so at first I was trying to multiply with too big value which didn't make sense. Now I got 'TPR_micro_Li6' and 'TPR_micro_Li7' match to 'total_TPR' with two decimal. So my question is that how close or equivalent those values should be? I have kept all available decimals in the atomic density calculations.

-Tommi

Ana Jambrina
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Re: Detector response

Post by Ana Jambrina » Thu Jul 22, 2021 1:52 pm

Each detector is scored independently and having its associated relative error. Multiplying each microscopic detector estimate by the corresponding atomic density for the given nuclide and summing up all the contributors to the total/macroscopic detector should result pretty much in the same outcome. You can check all the information about the materials in the ‘.out’ file, including composition, reaction channels, etc.

For a unit atomic density (single) material, microscopic and macroscopic cross sections are equivalent. Keep in mind that the density depends on the irradiation time.
- Ana

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