Difference: RadiationSimulationPublicResults (19 vs. 20)

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Radmons (May 2019)

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Total Ionizing Dose (TID) and 1 MeV equivalent neutron fluences are measured with RadFETs and diodes, respectively. These are located at 14 locations in the ATLAS ID and at 38 locations in calorimeters and muon detectors. In the Inner Detector radiation monitors are installed on the pixel support tube, on the ID end plate and on the cryostat wall. In LAr and Tile calorimeters monitors are installed near readout electronics and power supplies. Monitors are installed also on the Big Wheel and the Small Wheel of the muon detector. Response from radiation sensors increases with total integrated dose and fluence. Sensors are read out approximately once per hour and results are stored in the DCS database.

A set of graphs show doses and fluences at various locations as measured by the radiation sensors as the function of time during Run 2. Measurements are compared with doses and fluences predicted by Fluka and Geant4 simulation of radiation background, scaled with measured integrated luminosity. Summary plots show measured doses and fluences per unit of integrated luminosity and comparison with simulation.

In run 2 total the delivered luminosity is estimated to 160 ± 3 fb-1. This is slightly higher than the normally reported luminosity delivered in stable beams because for radiation exposure also the collisions outside of stable beam conditions have to be accounted for.

Simulation results are from a dataset of 50000 events generated by Pythia 8 with minimum bias tune A3 [3] and an assumed inelastic cross section of 78.42 mb at √s=13 TeV. The events were processed with FLUKA 2011 or Geant 4 [1,2] with the shielding physics list. A description of the ATLAS FLUKA simulation framework can be found in [4]. The geo tag for the Geant4 results is ATLAS-R2-2016-01-01-00.

The simulations are based on 3D models (simplified in case of FLUKA), but the radiation maps are averaged in azimuth. Not included in the simulated predictions are the systematic uncertainties associated withthe event generator, Geant4/FLUKA physics models, geometry description accuracies and the damage factors in deriving 1 MeV neutron equivalent fluences. The present estimate for the combined uncertainty from these sources is 50% in the ID volume, but assumed larger in the calorimeter and muon detector regions.

[1] GEANT4 Collaboration, GEANT4: a simulation toolkit, Nucl. Instrum. Meth. A 506 (2003) 250.
[2] ATLAS Collaboration, The ATLAS Simulation Infrastructure, Eur. Phys. J. C 70 (2010) 823, arXiv: arXiv:1005.4568 [physics.ins-det].
[3] ATLAS Collaboration, A study of the Pythia 8 description of ATLAS minimum bias measurements with the Donnachie-Landshoff diffractive model, ATL-PHYS-PUB-2016-017, https://cds.cern.ch/record/2206965
[4] S. Baranov et al., Estimation of Radiation Background, Impact on Detectors, Activation and Shielding Optimization in ATLAS, (2005), url: https://cds.cern.ch/record/814823.

 
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Total ionizing dose measured with REM RadFETs (0.13 um oxide thickness) on the Pixel Support Tube (PST) in the inner detector during run 2. The sensors are located at r = 23 cm and z = 90 cm at 4 different angles φ (0° and 180° on side C and 90° and 270° on side A).
 
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Red points represents measured values: points are averages from 3 sensors (one out of 4 failed) and error bars are calculated as E = √(σ2 + (σcal)2) , where σ is the standard deviation of measurements from 3 sensors and σcal = 0.2 *D is 20% accuracy of calibration. Only one point for every ~ 7 days is sown.

Black bands show Geant4 (left) and Fluka (right) simulation of doses at r and z coordinates of monitors on PST scaled by integrated luminosity. Dose (centre of the band) is calculated as D = Lint ∙ Dnorm where Lint is the integrated luminosity and Dnorm is the dose per unit of luminosity obtained from simulation. The width of the band represents standard deviation of Dnorm values in intervals of coordinates: r = 23 cm ± 1 cm and z = 90 cm ± 4 cm and the luminosity uncertainty. The total delivered luminosity in run 2 is estimated to 160 ± 3 fb-1 .

The simulations are based on 3D models (simplified in case of FLUKA), but the radiation maps are averaged in azimuth. Not included in the simulated predictions are the systematic uncertainties associated with event generator, Geant4/FLUKA physics models, geometry description accuracies. The present estimate for the combined uncertainty from these sources for dose estimates in the ID is 50%.

 
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Fluence (1 MeV neutron equivalent) measured with BPW34 diodes from bias voltage at 1 mA forward current on Pixel Support Tube. Sensors are located at r = 23 cm and z = 90 cm at 4 different angles φ (0° and 180° on side C and 90° and 270° on side A).

Red points represents measured values: points are averages from 4 sensors on PST and error bars are calculated as E = √(σ2 + (σcal)2) , where σ is the standard deviation of measurements from the four sensors and σcal = 0.2 *D is the 20% accuracy of calibration. Only one point for every ~ 7 days is sown.

Black bands show Geant4 (left) and Fluka (right) simulation of fluences at r and z coordinates of monitors scaled by integrated luminosity. Dose (centre of the band) is calculated as F = Lint ∙ Fnorm where Lint is the integrated luminosity and Fnorm is the fluence per unit of luminosity obtained from simulation. Width of the band represents standard deviation of Fnorm values in intervals of coordinates: r = 23 cm ± 1 cm and z = 90 cm ± 4 cm and the luminosity uncertainty. The total delivered luminosity in run 2 is estimated to 160 ± 3 fb-1 .

The simulations are based on 3D models (simplified in case of FLUKA), but the radiation maps are averaged in azimuth. Not included in the simulated predictions are the systematic uncertainties associated with event generator, Geant4/FLUKA physics models, geometry description accuracies and the damage factors in deriving 1 MeV neutron equivalent fluences. The present estimate for the combined uncertainty from these sources for fluence estimates in the ID is 50%.

 
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Fluence (1 MeV neutron equivalent) measured from reverse current in 25 μm thick epitaxial diodes in the Inner Detector End Plate. On ID End Plate sensors are located at r = 54 cm and z = 345 cm at 4 different angles φ (105° and 285° on side C and 15° and 195° on side A).

Blue points represents measured values: points are averages from 3 sensors (one of the 4 failed) and error bars are calculated as E = √(σ2 + (σcal)2) , where σ is the standard deviation of measurements from the three sensors and σcal = 0.2 *D is the 20% accuracy of calibration. Only one point for every ~ 7 days is sown.

Black bands show Geant4 (left) and Fluka (right) simulation of fluences at r and z coordinates of monitors scaled by integrated luminosity. Dose (centre of the band) is calculated as F = Lint ∙ Fnorm where Lint is the integrated luminosity and Fnorm is the fluence per unit of luminosity obtained from simulation. Width of the band represents standard deviation of Fnorm values in intervals of coordinates: r = 54 cm ± 2 cm and z = 345 cm ± 3 cm and the luminosity uncertainty. The total delivered luminosity in run 2 is estimated to 160 fb-1 ± 3 fb-1 .

The simulations are based on 3D models (simplified in case of FLUKA), but the radiation maps are averaged in azimuth. Not included in the simulated predictions are the systematic uncertainties associated with event generator, Geant4/FLUKA physics models, geometry description accuracies and the damage factors in deriving 1 MeV neutron equivalent fluences. The present estimate for the combined uncertainty from these sources for fluence estimates in the ID is 50%.

 
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Summary of measurements and simulations of TID (left) and 1 MeV neutron equivalent fluences (right) per unit of integrated luminosity in the Inner Detector during Run 2. Measurements are averages from sensors at same (r, z) but at different azimuth angles. Error bars include variation of dose/integrated_luminosity ratios during run 2, variations between sensors and 20% uncertainties of calibration. TID is measured with REM 0.13 um RadFETs. Neutron equivalent fluence is measured with two types of sensors at each location: BPW34 diodes (forward bias) and epitaxial diodes (reverse bias). In run 2 delivered luminosity contributing to radiation dozes is estimated to be 160 fb-1 ± 3 fb-1 . Error bars on simulation (Geant4 and Fluka) points are standard deviations of simulated doses and fluences per fb-1 in intervals of coordinatesaround monitoringlocation:r:±1cm,z:±4cmonPST, r:±2cm,z:±3cmontheIDEndPlateandr:±2cm,z:±4cmonthe cryostat wall.

The simulations are based on 3D models (simplified in case of FLUKA), but the radiation maps are averaged in azimuth. Not included in the simulated predictions are the systematic uncertainties associated with event generator, Geant4/FLUKA physics models, geometry description accuracies and the damage factors in deriving 1 MeV neutron equivalent fluences. The present estimate for the combined uncertainty from these sources is 50% for both radiation quantities in the ID region.

 
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TID and 1 MeV eq. neutron fluence measured with radiation monitors in the Muon detector during run 2. Doses are measured with LAAS RadFETs (1.6 um thick oxide) and fluences are measured with high sensitivity PiN diodes (CMRP) under forward bias. Sensors are installed on Small Wheels at r ~ 2.1 m and z ~ 6.9 m and on Big Wheels at r ~ 2.1 m and z ~ 6.9 m at four azimuthal angles (0,90,180 and 270) on sides A and C. On Small Wheels 7 out of 8 and on Big Wheels 3 out of 8 sensors were operating during run 2.

Points with error bars represent measured values: points are averages from sensors at same r and z and error bars are calculated as E = √(σ2 + (σcal)2) , where σ is the standard deviation of measurements and σcal = 0.2 *D is the 20% accuracy of calibration. Only one point for every ~ 7 days is shown.

Hatched bands show Geant4 simulation of doses and fluences at monitoring locations. Dose (centre of the band) is calculated as D = Lint ∙ Dnorm where Lint is the integrated luminosity and Dnorm is the fluence per unit of luminosity obtained from simulation at r and z coordinates of monitors. Width of the band represents standard deviation of Dnorm values in ± 10 cm intervals of r and z coordinates around the monitoring location. The total delivered luminosity in run 2 is estimated to 160 ± 3 fb-1 .

The simulations are based on 3D models (simplified in case of FLUKA), but the radiation maps are averaged in azimuth. Not included in the simulated predictions are the systematic uncertainties associated with event generator, Geant4/FLUKA physics models, geometry description accuracies and the damage factors in deriving 1 MeV neutron equivalent fluences.

 
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Summary of measurements and simulations of TID (left) and 1 MeV equivalent fluences (right) per unit of integrated luminosity in LAr and Tile calorimeters and in muon detector for run 2. Measurements are averages from sensors at same (r, z) but at different azimuth angles. Error bars include variation of dose/integrated_luminosity ratios during run 2, variations between sensors and calibration uncertainties. The total delivered luminosity in run 2 is estimated to 160 ± 3 fb-1 . Error bars on simulation (Geant4 and Fluka) points are standard deviations of simulated doses and fluences per fb-1 in intervals of coordinates around monitoring location: r: ± 10 cm, z: ± 10 cm.

The simulations are based on 3D models (simplified in case of FLUKA), but the radiation maps are averaged in azimuth. Not included in the simulated predictions are the systematic uncertainties associated with event generator, Geant4/FLUKA physics models, geometry description accuracies and the damage factors in deriving 1 MeV neutron equivalent fluences. The large TID difference observed in two of the LAr regions is where the material distribution is particularly complex, with strong variations in azimuth, and this is likely to be oversimplified in the simulations.

 
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Graph shows the increase of base current at 10 uA collector current in DMILL bipolar transistors on Pixel Support Tube in run 2. Points are average values from 8 sensors on PST (there are 2 transistor at each monitoring location). Error bars are calculated as E = √(σ2 + (σcal)2), where σ is the standard deviation of measurements from 8 sensors and σcal = 0.2* ΔIb is the 20% systematic uncertainty of measurement. Only one point for every ~ 7 days is shown. The same type of transistor is used in the input stage of the ABCD3TA chip, the readout chip of the Semiconductor Tracker (SCT). The rise of the base current is one of the causes for radiation induced increase of noise in the readout chip. The increase of the base current is the consequence of displacement damage in the base of the transistor. Equivalent fluence of 1 MeV neutrons is the quantity measuring the amount of displacement damage caused by energetic hadrons. In addition, in this particular type of transistors, also thermal neutrons contribute significantly to displacement damage via fragments from B + n -> Li + α reaction in highly doped p+ region near the base. Effects are additive: ΔIb = keq·Фeq + kth ·Фth where Фeq is 1 MeV neutron equivalent fluence and Фth is the fluence of thermal neutrons and keq and kth are measured in calibration irradiations. The increase of base current measured on PST and other locations in the ID is smaller than expected from simulated fluences of 1 MeV equivalent and thermal neutrons. Measured base current increase could be attributed to the effect of fast hadrons (Фeq) alone. This indicates that thermal neutron fluences may be overestimated in simulations. However, because of systematic uncertainties in calibration, the effect of thermal neutrons can not be excluded and reliable estimation of thermal neutron fluences can not be made from these measurements.
 
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