Calibration of Single Phase Liquid Argon Detectors

Calibration of Single Phase Liquid Argon Detectors

Kimberly J. PalladinoMIT

MiniCLEAN Collaboration

1Tuesday, July 24, 2012

Outline

Single Phase Liquid Argon technique

Calibration Goals

Internal calibration sources

External gamma sources

External neutron sources

Optical calibration


Single Phase Liquid Argon

Scintillation in LAr at 128 nm, requires wavelength shifter, TPB, to allow PMT detection

Pulse shape discrimination (PSD) based on triplet lifetime of 1.6 us and singlet lifetime of 6 ns

Fprompt, PSD variable, low (~0.3) for electronic recoils, and high (~0.8) for nuclear recoils

Position reconstruction based on charge distribution and timing in larger detectors


Calibration goals

Internal Sources

Gamma Sources

Neutron Sources

Light Injection

Sing

le P

E

Ener

gySc

ale

Ener

gyRe

solu

tion

Posi

tion

Reco

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PSD

Surf

ace

Even

ts39

Ar/

PSD

Leak

age

Neu

trons

Nuclear recoilsElectronic recoils4

Tuesday, July 24, 2012

39Ar

Naturally occurring 39Ar in atmospheric argon with activity of 1 Bq/kg

First forbidden beta decay with analytically defined spectral shape

Spectrum known to 1% down to 10 keV

Endpoint at 565 keV

Half-life of 269 years

Uniform distribution in detector

Continuous calibration


39Ar: Energy Scale

Triplet tail from 39Ar allows constant monitoring of the single photo-electron spectrum and every individual PMT’s gain

Continuous detector health, including triplet lifetime

MiniCLEAN will see ~800 kHz of 39Ar

Light-yield measured in going from PE to keVee

1 day gives a statistical LY measurement to better than 1%


39Ar: Position Reconstruction

Uniformity gives r2 relation in differential rates

Allows daily studies of radial bias and position reconstruction

Large datasets outside WIMP ROI

Energy dependent studies


39Ar: Pulse Shape DiscriminationProbe of the electronic recoil rejecting pulse shape discrimination variable (Fprompt) with all events outside the fiducial volume

But surface alpha and neutron events will have to be taken into account

MiniCLEAN planning an 39Ar Spike, 5-10x natural abundance after Dark Matter run to demonstrate PSD in larger detectors and investigate potential backgrounds

Fast reactor irradiation of KF/KCl utilizing 39K(n,p)39Ar as is done in radiometric dating

UV ablated muscovite@ NM GeochronologyResearch Laboratory


83Krm

83Rb (trapped in charcoal) decays with a half-life of 86.2 days to 83Krm 75% of the time, which, as a Noble gas flows into the detector

83Krm subsequently emits two conversion electrons with a total energy of 41.5 keV and a half-life of 1.83 hours

Calibrates energy as a function of position -> no sign of freeze out in MicroCLEAN

Planned calibration for KATRIN arXiv.org:0109033v1 and also studied for LXe detectors Kastens et al. JINST 5(2010) P05006 and Manalaysay et al. Rev. Sci.Instrum 81 (2010) 073303

Lippincott et al. Phys.Rev.C81:045803. 2010. arXiv:0911.5453.

83Krm energy spectrum after background subtraction

in MicroCLEAN


External Gamma SourcesAdditional energy and position calibration, especially for high radius events

Tagged sources allow reduction of the 39Ar background during calibration

DEAP-3600 can study neck region events

22Na: e+ and 1.274 MeV γ used by both MicroCLEAN and DEAP-1, MiniCLEAN tagged source

60Co: 1.17 and 1.33 MeV γ DEAP-3600 tagged source

Also considered:

137Cs: 662 keV γ

57Co: 122, 136, 692 keV γ

Isotopes DEAP-3600

MiniCLEAN


Neutrons: D-D generatorNuclear recoil PSD and energy calibration, test neutron tagging and verify simulation physics

Primary calibration through dd-interaction

Using Schlumberger MiniTron allowing pulsed and DC mode operation

At 40kV, the neutron yield is 103 n/uC resulting in 105n/s at 50 uC


D-D Neutron Simulations

MiniCLEAN studies show 1.1% of generated neutrons in fiducial volume and energy ROI, lower for larger, acrylic shielded DEAP-3600

Liskien & Paulsen (1973)J. Walding12.5-25 keVee, r<295 mm 12.5-25 keVee, r>295 mm


D-D System

Power supplies and control electronics operating since 2010

Moving from prototype canister (shown) to final canister

Deployment system under construction at RHUL. Moveable with size of 1.0m x 0.8m x 2.8m


Neutrons: Hot PMT

MiniCLEAN pursuing a “Hot PMT” calibration source to reproduce most dangerous neutron background

Will mix 5.3 g of 238U and 16g of 232Th in melted PMT glass to produce 1 n/s

Tagged source with scintillator to see alpha, n de-excitation gammas

Currently prototyping with 2 lbs of uranium borosilicate with 16 g (1.8%) 238U

pre WW-II with more daughters, but expected rate of 3 n/s

M. Akashi-Ronquest


Optical Calibration: DEAP-3600Optics before and after TPB deposition

LEDball in diffuser, lowered through neck: 425 nm before TPB deposition, 250 nm after

Optics stability, timing

Distributed light by fibers to PMTs ,light will reflect into the detector

Light leakage from neck: laser light injection


Optical Calibration: MiniCLEANProbe visible and UV optics, and surface event position reconstruction

6 UV (254 nm) and 6 Blue (465 nm) LEDs, in the LAr with fibers running to face of pentagonal lightguides

Kapustinsky pulser allows fast pulses as expected from prompt argon scintillation

20 ns trigger pulse

Kapustinsky trigger pulse


CalibratorsDEAP-3600

RHUL: dd-neutrons,

light injecton

RAL: gammas, 83Krm

Sussex: light injection

Queen’s: 39Ar

SNOLab: 39Ar, gammas

MiniCLEAN

LANL: 39Ar, gammas, Hot PMTs, 83Krm

MIT: dd-neutrons, 83Krm

RHUL: dd-neutrons

UNM: light injection


Conclusion

Both DEAP-3600 and MiniCLEAN have developed calibration plans with multiple handles on each experimental parameter

39Ar, though a background, is an excellent calibration source too!

Both experiments will have exciting year’s as they build, and calibrate, the detectors!


Collaborations


Calibration of Single Phase Liquid Argon Detectors

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