Pulsed Neutron Source for Liquid Argon TPC Calibration Jingbo Wang University of California, Davis, Department of Physics Workshop on Calibration and Reconstruction for LArTPC Detectors 2018/12/11, Fermilab
Outline § Why neutron source? § How does the neutron source work? § How to use the neutron source? § Neutron capture study § Conclusion Workshop on Calibration and Reconstruction for LArTPC Detectors, December 11th, 2018 Slide 2
Needs for LArTPC Calibration § For LArTPC, it is essential to understand the detector effects and develop calibration scheme to precisely determine the amount of energy deposition. § In LArTPC, the amount of detected charge is not always uniform throughout the whole volume. It depends on many factors: – Electrical field distortion, space charge – Electron lifetime (argon impurity) – Electron-ion recombination – Noise level § It is highly desirable to have a "standard candle" energy deposition that can be detected for different positions throughout the detector volume Workshop on Calibration and Reconstruction for LArTPC Detectors, December 11th, 2018 Slide 3
Why Neutron Source? § cosmic muons and Michel electrons could be used, however – Limited if deep underground: In DUNE, expect 4000 cosmics/day/10 kt -> 30 stopping muons and 20 Michel electrons § Radioactive source with known energy could be used, however – The source must be physically placed at the point of interest inside the cryostat – Need to deploy in low electrical field to minimize induced E-field distortions § One way around these issues is to use an external neutron source, which is a newly developed calibration technique. § All different calibration systems are complementary Workshop on Calibration and Reconstruction for LArTPC Detectors, December 11th, 2018 Slide 4
How does it work? § The neutron anti–resonance “dip” in the cross-section makes 40-Ar near transparent to 57 keV neutrons § 38-Ar and 36-Ar have different resonance structures that keep the natural argon from being totally transparent § The effective mean free path in natural argon is ~30 m 40-Ar, 99.6035% ! = 1.5 km @ 57 keV 36-Ar 36-Ar, 0.3336% ! = 16 cm @ 57 keV 38-Ar, 0.0634% ! = 47 cm @ 57 keV 40-Ar 38-Ar 57 keV anti-resonance Workshop on Calibration and Reconstruction for LArTPC Detectors, December 11th, 2018 Slide 5
How Does it Work? 18-Ar-40 EL Cross-section In Ar-40, the width of the the anti- § resonance window is 20 keV . The fractional energy loss is 4.8% per scatter Statistically, most neutrons above § anti-resonance energy could fall into the anti-resonance window ∆ " , # = # $ − # ' = 1 * − 1 2 1 − # $ # $ * + 1 Once in the window, it takes a § few scatters for the neutron to get out § The neutrons are thermalized and captured, emitting 6.1 MeV gamma cascade as a “standard candle” for detector calibration If we can produce anti-resonance neutrons, we could “deliver” the neutron captures to a very far distance. Workshop on Calibration and Reconstruction for LArTPC Detectors, December 11th, 2018 Slide 6
How to make anti-resonance neutrons? § Neutron source sits on top of Cryostat. Cryostat insulation has to be removed, but there is no need to open the Cryostat membrane § DD generator produces 2.5 MeV initial neutrons § Fe-S-Li moderator reduces the energy down to 73 keV § Ni neutron reflector increases the flux Elastic scattering cross-section 32-S 40-Ar Workshop on Calibration and Reconstruction for LArTPC Detectors, December 11th, 2018 Slide 7
Geant4 Simulation for DUNE-size TPC One neutron source can illuminate half of the DUNE-size TPC Neutron spread in a 60m × 10m × 8m LArTPC Workshop on Calibration and Reconstruction for LArTPC Detectors, December 11th, 2018 Slide 8
How to use the source? § It’s pulsed: plenty of neutron captures allow fast calibration run – Up to 10 7 neutrons/pulse from DD generator – More than 20,000 neutron captures/pulse in DUNE-size TPC § It’s in situ: detector energy response measurement – t 0 provided by DD generator (rough) or the photodetector (precise) – Can provide fixed charge deposition as a function of (x, y, z) throughout the TPC volume § It’s “standard”: a “standard candle” for energy deposition calibration – The total 6.1 MeV neutron binding energy is visible in the form of gamma cascade. – Possible to see the energy spectrum from individual gammas § Could help to improve high-level neutrino energy reconstruction : deserves more study § Test of SN trigger efficiency Workshop on Calibration and Reconstruction for LArTPC Detectors, December 11th, 2018 Slide 9
Energy deposition calibration § Need to understand the neutron capture very well: ACED experiment that was done last year at Los Alamos National Laboratory § Need to develop a neutron capture tagging algorithm in liquid argon TPC: simulations have shown promising results Predicted Measured by GEANT by ACED 4.7 MeV 167 keV 1.2 MeV Workshop on Calibration and Reconstruction for LArTPC Detectors, December 11th, 2018 Slide 10
How to Identify Neutron Captures Input: Neutron capture with G4 step point gamma cascade emission Gamma 167 keV 2.6 MeV 3.4 MeV 167 keV 2.6 MeV 3.4 MeV vertex Input: 30 cm Output: clustered electrons Method: 3D clustering + electron counting Workshop on Calibration and Reconstruction for LArTPC Detectors, December 11th, 2018 Slide 11
Clustering can identify individual gammas § The clustering works well, but has to be done in 3D. § Smearing due to electron lifetime, electron diffusion, velocity variation and recombination is not simulated, but we expect mm-level effects § Need to do a more realistic simulation 516 keV 167 keV 1.2 MeV 516 keV 4.7 MeV 6.1 MeV 167 keV 1.2 MeV 4.7 MeV Workshop on Calibration and Reconstruction for LArTPC Detectors, December 11th, 2018 Slide 12
Argon Capture Experiment at DANCE § DANCE has nearly 4 ! coverage § DANCE is a sphere of 160 BaF 2 crystals, each couples to a PMT § High segmentation allows gamma multiplicity measurement § Neutron energies obtained using Time-of-Flight § Upstream monitors measure energy-dependent neutron beam flux John Ullman Detector for Adva vanced Neutron Capture Experiments (DANCE) Workshop on Calibration and Reconstruction for LArTPC Detectors, December 11th, 2018 Slide 13
ACED measurement § ACED measured the thermal neutron capture cross-section and the correlated-gamma cascade § The data is now being analyzed to reconstruct individual gammas on an event-by-event basis. § Will provide precise capture cross-sections around thermal energies § Will provide the simulation software with a database of gamma cascades Predicted Measured by GEANT by ACED 4.7 MeV 167 keV 1.2 MeV Workshop on Calibration and Reconstruction for LArTPC Detectors, December 11th, 2018 Slide 14
Neutron Capture Cross-section § Using Time-of-Flight, the neutron velocity can be calculated on event-by- event basis (never done for Ar before ACED). § Data analysis nearly complete. Still need to further analyze the data for beam normalization § Just did a beam normalization measurement last week. § Paper to be published soon Credit: Luca Pagani × 3 2 10 (mb) After ACED Before ACED ENDF/B-VII.1 σ W. Koehler (1963) R.L.D. French et al. (1965) 3 10 N. Ranakumar et al. (1969) from fit × 2 5 10 × 2 4 10 × 2 3 10 × 2 2 10 − − − × 2 1 × 1 2 10 10 2 10 1 2 E (eV) n Workshop on Calibration and Reconstruction for LArTPC Detectors, December 11th, 2018 Slide 15
Future Elastic Scattering Experiment measurement § At 57 keV, the theory predicts that there is a “deep” anti-resonance dip § Previous measurement doesn’t agree with the theory (a factor 100 difference) § The sensitivity of previous measurement is limited § Measurement needs to be done with high precision Workshop on Calibration and Reconstruction for LArTPC Detectors, December 11th, 2018 Slide 16
Neutrons are Important in LArTPC § To turn neutrino physics into a precision science, we need to understand the complex neutrino- nucleus interactions – Neutrons carry away a large fraction of energy – Neutron yield is model dependent – Neutrons are hard to detect in LArTPC § Understanding the neutrons are also essential for low energy physics – Modeling the supernova event – Tagging the neutron background for dark matter and 0 !"" searches Workshop on Calibration and Reconstruction for LArTPC Detectors, December 11th, 2018 Slide 17
Conclusion § External Pulsed Neutrons Source can be used to calibrate the liquid argon TPC § Feasibility study has shown the neutrons can illuminate a large volume of the TPC, providing 6.1 MeV gamma cascades as a “standard candle” for energy deposition calibration. § Simulation has shown that 3D clustering can identify individual correlated gammas § We did the ACED experiment to understand the neutron capture, and will do another experiment to understand the neutron scattering § First test possibly at ProtoDUNE Workshop on Calibration and Reconstruction for LArTPC Detectors, December 11th, 2018 Slide 18
Backup Workshop on Calibration and Reconstruction for LArTPC Detectors, December 11th, 2018 Slide 19
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