R&D on Liquid-Scintillator Detectors

R&D and Astroparticle PhysicsLisbon, January 8th 2008

Michael WurmTechnische Universität München

Organic Liquid Scintillators

high light yieldfast fluorescence decayparticle-dependent response

good energy resolutiontime resolution of nsbackground discrimination

solar, geo ‘s, 20proton decayall

handling of large volumes

possible purification

solubility of foreign atoms

large target mass, self-shieldinghigh radiopurity, low thresholddoping of the target

all

solar ‘s

20, reactor ‘s

target consists of Hydrogen and Carbon

free protonshigh p/n ratio

antineutrinosproton decay

liqui

dsc

intil

lato

ror

gani

c

→ liquid-scintillator detectors are adapted for rare-event searches,such as low-energetic neutrinos, proton decay and 20 decay

→ detectors can be adjusted to the detection of individual particles

Upcoming liquid-scintillator detectors:SNO+/++

1ktNOvA

30kt

LENA, 50kt

HanoHano, 10kt or moreSuperNEMO

LENS>200t

Daya Bay, Angra …

Borexino – a running LS experiment

300t of PC, Ø 13m,2200 phototubes

light yield:500 pe/MeV

energy resolution:0.04 @ 1 MeV

threshold:hardware: 40keV14C: ~200keV

pulse shape discriminitation of ,statistical at a level of ~10-3

high-level radiopurity:e.g. U/Th contamination <10-17 g/g

7Be‘s already measuredpep, CNO‘s seem well feasible

210Po ‘s7Be ‘s

SNO+ SNO++

replacing the D2Oinside the acrylicsphere with liquidscintillator(LAB)

physicspotential:

• solar ’s pep, CNO• reactor ’s oscillation dip• terrestrial ’s favourable S/B ratio• ~500 SN events (10kpc)

loading the scintillatorwith 0.1% Neodynium

→ 50-500 kg 150Nd:20 @ 3.3 MeV

physicspotential:

• large rates:spectral fit to

2/0 signals• predicted potential:

masses down to80 - 30 meV

LENAa multi-purpose observatory

solar neutrinos5x103 7Be e events per day

sign of time-dependent fluctuations?pep (210ev/d), 8B@13C (360/a)

→ test MSW transition regionCNO contribution to fusion

Supernova neutrinos 2x104 ev for SN@10kpc

8 different reaction channels →disentangle neutrino flavours,flux and spectral information mass hierarchy,13, MSW

terrestrial anti-neutrinos~103 events per yearrelative crust-abundancies of U/Thfavourable S/B conditionslook for a georeactor of >2TW

proton decay into K+favoured by SUSY, < 1035 yrsefficiency ~67% as K+ is visible!1 background event in 10 yrs→ p > 41034 yrs (90% C.L.)

Wurm et al., PRD 75 (2007) 023007, astro-ph/0701305

Hochmuth et al., Astrop.Phys 27, 21, hep-ph/0509136

T. Marrodán Undagoitia et al., PRD 72 (2005) 075014

_

Diffuse SN neutrinos2-20 antineutrinos per year

excellent background rejection: 1ev/yrspectroscopy possible: info on

both SN rate (z<2) and SN modelsNeutrino/Beta BeamsIndirect Dark Matter Search

Scintillator Components

SolventPC, PXE, LAB … target fp/p/n-ratiospurification, addition of oil energy transfer to fluor

propagation of scint. light

Wavelength Shifter (Fluor)PPO, bisMSB, PMP … signal decay timescombinations possible large Stoke‘s shifts

no self-absorption

Additionsn/ catchers (Gd, In …) stability of the scintillator candidates (Nd, …) absorption of scint. light

all these properties have to be investigated …

Work @ TUM

light yieldat

tenu

atio

n le

ngth

scattering length

fluorescence time & spectra

Solvent Candidates

LAB, C16-19H26-32

density: 0.86 kg/llight yield: ~100%fluorescence decay: ~ 6nsattenuation length @ 430nm:

~20m

PXE, C16H18

density: 0.99 kg/llight yield:

~10.000 ph/MeVfluorescence decay: ~ 3nsattenuation length @ 430 nm:

≤12m (mostly scattering)

+80% Dodecane, C12H26

density: ~0.80 kg/llight yield: ~85%fluorescence decay slowerattenuation length increases!

In terms of solvent transparency,a 30m diameter detector is feasible.

• effects and complexity of purification have to be considered.

PPO, C15H11NO

primary fluorabsorption band:

280-325nmemission band:

350-400nm

bisMSB, C24H22

secondary fluorabsorption band:

320-370nmemission band:

380-450nm

Possible Wavelength Shifters• large detectors require Stoke‘s Shift to wavelength of

430 nm where scintillator is more transparent

• a combination of a primary and a secondary shifter can be used→ might lead to self-absorption

• fluors with large Stoke‘s Shifts like PMP have to be tested

• other parameters like fluorescence time, solubility etc. have to be considered as well

The Aim: A detailed MC study of light production and propagation in a large-

volume detector like LENA.

Further R&D on liquid scintillators

• Intrinsic Purity of the Scintillator:Production, Handling, Transport

• Purification Methods, both Transparency and Radiopurity:Column-Chromotography (Silica Gel, Al2O3 etc.),Distillation, Water-Purging …

• Scinitillation Light Production and Propagation:Wavelength-dependent emission, absorption and scattering of the lightExperiments and MC simulations for energy & time resolution

• Investigation of New Materials:solvents: high transparency, short signal decay time …fluors: overlap of absorption with solvent emission, large Stoke‘s shifts (>430nm)

LENA design

detector location:• cavern or deep-sea • overburden of >4000 m.w.e.• for most purposes: far away from nuclear power plants

upright posititon favourable for buoyant forces, assembly etc.

detector dimensions adjusted to transparency of the scintillator

30% optical coverage

light yield: >200 pe/MeV

buffer shields the target from external radioactivity

radiopurity as in Borexino (?)

target volume50kt of liquid scintillatorh 100m, Ø 26m

buffer volume solvent&quencherthickness: 2m

muon vetopanels of plastic scintillator

nylon vessel

steel tank~13k phototubes

water tank>5m n shieldingactive veto (?)

egg-shaped cavernh 120m, Ø 50m

R&D needs of the Detector

• Construction of the Cavern:maximum depth, shape, maximum size,infrastructure for scintillator, (liquid) gases …

• Materials of the Detector:treatment of the steel (inertness, low reflectivity),construction of nylon vessel, …

• Photo-Detection:PMTs or alternative light detectors,optimization of optical coverage (light concentrators …)

• Infrastructure of HV, Electronics

Liquid-Scintillator Detectors provide good energyresolution, particle identification and favourablebackground conditions at a relatively low price.

• Large-volume detectors like LENA will be multi-purpose observatories and will address a widerange of interesting questions comprisingparticle, astro-particle and geophysics.

• Purity and purification of materials, constructionof large & deep underground caverns andoptimization of photodetection are examplesfor possible synergies with other experiments(LAGUNA: Memphys, Glacier & Lena).

Outlook