Pulsed Neutron Source for Liquid Argon TPC Calibration Jingbo Wang - - PowerPoint PPT Presentation

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

Workshop on Calibration and Reconstruction for LArTPC Detectors, December 11th, 2018

Outline

§ Why neutron source? § How does the neutron source work? § How to use the neutron source? § Neutron capture study § Conclusion

Slide 2

Workshop on Calibration and Reconstruction for LArTPC Detectors, December 11th, 2018

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

Slide 3

Workshop on Calibration and Reconstruction for LArTPC Detectors, December 11th, 2018

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

Slide 4

§ 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

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

Slide 5

36-Ar, 0.3336% ! = 16 cm @ 57 keV 40-Ar, 99.6035% ! = 1.5 km @ 57 keV 38-Ar, 0.0634% ! = 47 cm @ 57 keV

40-Ar 38-Ar 36-Ar

57 keV anti-resonance

Workshop on Calibration and Reconstruction for LArTPC Detectors, December 11th, 2018

Slide 6

§ 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 § Once in the window, it takes a few scatters for the neutron to get

• ut

§ The neutrons are thermalized and captured, emitting 6.1 MeV gamma cascade as a “standard candle” for detector calibration

18-Ar-40 EL Cross-section

∆ " # #$ = #$ − #' #$ = 1 2 1 − * − 1 * + 1

,

If we can produce anti-resonance neutrons, we could “deliver” the neutron captures to a very far distance.

How Does it Work?

Workshop on Calibration and Reconstruction for LArTPC Detectors, December 11th, 2018

How to make anti-resonance neutrons?

Slide 7

§ 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 40-Ar 32-S

Workshop on Calibration and Reconstruction for LArTPC Detectors, December 11th, 2018

Geant4 Simulation for DUNE-size TPC

Slide 8

Neutron spread in a 60m × 10m × 8m LArTPC

One neutron source can illuminate half of the DUNE-size TPC

Workshop on Calibration and Reconstruction for LArTPC Detectors, December 11th, 2018

How to use the source?

§ It’s pulsed: plenty of neutron captures allow fast calibration run – Up to 107 neutrons/pulse from DD generator – More than 20,000 neutron captures/pulse in DUNE-size TPC § It’s in situ: detector energy response measurement – t0 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

Slide 9

Workshop on Calibration and Reconstruction for LArTPC Detectors, December 11th, 2018

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

Slide 10

167 keV 1.2 MeV 4.7 MeV

Predicted by GEANT Measured by ACED

Workshop on Calibration and Reconstruction for LArTPC Detectors, December 11th, 2018

Slide 11

167 keV 2.6 MeV 3.4 MeV

Input: Output: clustered electrons

How to Identify Neutron Captures

167 keV 2.6 MeV 3.4 MeV 30 cm vertex G4 step point Gamma

Method: 3D clustering + electron counting Input: Neutron capture with gamma cascade emission

Workshop on Calibration and Reconstruction for LArTPC Detectors, December 11th, 2018

Clustering can identify individual gammas

Slide 12

§ 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

4.7 MeV 6.1 MeV 1.2 MeV 516 keV 516 keV 167 keV 167 keV 4.7 MeV 1.2 MeV

Workshop on Calibration and Reconstruction for LArTPC Detectors, December 11th, 2018

Argon Capture Experiment at DANCE

Slide 13

Detector for Adva vanced Neutron Capture Experiments (DANCE)

§ DANCE has nearly 4! coverage § DANCE is a sphere of 160 BaF2 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

Workshop on Calibration and Reconstruction for LArTPC Detectors, December 11th, 2018

ACED measurement

Slide 14

§ ACED measured the thermal neutron capture cross-section and the correlated-gamma cascade § The data is now being analyzed to reconstruct individual gammas

• n 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

167 keV 1.2 MeV 4.7 MeV

Predicted by GEANT Measured by ACED

Workshop on Calibration and Reconstruction for LArTPC Detectors, December 11th, 2018

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

Slide 15

2 −

10 × 2

1 −

10

1 −

10 × 2 1 2 (eV)

n

E

2

10 × 2

2

10 × 3

2

10 × 4

2

10 × 5

3

10

3

10 × 2 (mb) σ

ENDF/B-VII.1

• W. Koehler (1963)

R.L.D. French et al. (1965)

• N. Ranakumar et al. (1969)

Before ACED After ACED

from fit

Credit: Luca Pagani

Workshop on Calibration and Reconstruction for LArTPC Detectors, December 11th, 2018

Future Elastic Scattering Experiment measurement

Slide 16

§ 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

Neutrons are Important in LArTPC

Slide 17

§ 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

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

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Workshop on Calibration and Reconstruction for LArTPC Detectors, December 11th, 2018

Backup

Slide 19

Workshop on Calibration and Reconstruction for LArTPC Detectors, December 11th, 2018

Advantage of DD Generator

§ DD Generators are commercial devices that could provide a source of low energy (2.5 MeV) neutrons. § 2.5 MeV is well below the neutron and proton separation energy of most elements – little activation expected. § Monoenergetic spectrum (unlike TT) which will simplify neutron degrader design and shielding § Costs are low (~$100k) and they can be operated in pulse mode to give a trigger signal.

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Workshop on Calibration and Reconstruction for LArTPC Detectors, December 11th, 2018

Candidate DD source

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Workshop on Calibration and Reconstruction for LArTPC Detectors, December 11th, 2018

Neutrons in SN events

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§ Missing the emitted neutron leads to a large error on the reconstructed neutrino energy § Several difficulties in modeling this process

– Elastic scattering cross-section below 100 keV was not well-measured – The event-by-event capture γ- ray distributions are unmeasured (would be valuable to tag these neutrons) – The thermal (n,γ) cross section is poorly measured

§ Measurements of the neutron transport properties are needed § The current MARLEY models suggest that 15-30% of supernova νeCC events will involve neutron emission

Workshop on Calibration and Reconstruction for LArTPC Detectors, December 11th, 2018

Neutrons in Low Background Experiments

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Workshop on Calibration and Reconstruction for LArTPC Detectors, December 11th, 2018

Optimization: Moderator study

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§ Materia must have medium elastic scattering and low absorption for neutrons § Fe was chosen as the most efficient moderator to degrade the neutron energy from 2.5 MeV to less than 1 MeV § Best Fe thickness is 17 cm

S.Conlon

Workshop on Calibration and Reconstruction for LArTPC Detectors, December 11th, 2018

Optimization: Filter study

Slide 25

§ The filter further reduces the neutron energy and transmits neutrons at anti- resonance energy § Liquid argon itself is the best filter but the need for a cryostat brings complication § Sulfur is a good filter due to its n 73 keV anti-resonance for neutron elastic scattering § Thickness of Sulfur filter was studied

S.Conlon

Workshop on Calibration and Reconstruction for LArTPC Detectors, December 11th, 2018

Optimization: Shielding study

Slide 26

§ Lithium-Polyethylene is used as the shielding material § Shield is to block both neutrons and gammas from neutron capture § 2.2 MeV gamma peak is from neutron capture on hydrogen § Shield can effectively block the lower energy gammas peaks but is only able to degrade 2.2 MeV gammas § The dose of radiation form 2.2 MeV gammas is 1.8 x 10-7 mrem per pulse (106 neutrons) for a person standing 1 meter away from the source § The source could run 7.7 x 107 shots per day being compliant with the limit ( 5 merm annual radiation dose) set by Nuclear Regulation Commission (NRC)

12 cm Lithium-Polyethylene

S.Conlon

Workshop on Calibration and Reconstruction for LArTPC Detectors, December 11th, 2018

Neutron Energy Moderation

Slide 27

Workshop on Calibration and Reconstruction for LArTPC Detectors, December 11th, 2018

Slide 28

516 keV 5.5 MeV

Input: Output:

Clustering can identify individual gammas

Workshop on Calibration and Reconstruction for LArTPC Detectors, December 11th, 2018

Slide 29

167 keV 2.6 MeV 3.4 MeV

Input: Output:

Clustering can identify individual gammas

Workshop on Calibration and Reconstruction for LArTPC Detectors, December 11th, 2018

Slide 30

167 keV 1.2 MeV 4.7 MeV

Input: Output:

Clustering can identify individual gammas

Workshop on Calibration and Reconstruction for LArTPC Detectors, December 11th, 2018

An example: electron lifetime

§ Electron lifetime can be obtained using the relation: !"#$%&'#( = !*'&##+*(',-*

.

§ The drift time can be determined by either:

– Rough t0 provided by the DD generator: the drift time will be smeared by the DD neutron pulse width (can be tuned down to 10 μs level) and the neutron life time (1 μs thermalization time + 100 μs capture time) – Precise t0 provided by the photodetector system: no smearing due to the neutron lifetime, but need low intensity operation to avoid photodetector pileup.

§ Ideally, measure the electron lifetime for every m3 volume.

Slide 31