christian buck, mpik heidelberg

Christian Buck, MPIK Heidelberg

LowNu

Reims, October 2009

Liquid scintillators

Christian BuckMPIK Heidelberg

Reims, Neutrino Champagne 2009

Overview

Introduction

Scintillator components

Energy transfers

Metal loaded scintillators

Summary



Liquid scintillator past

Metal loaded:

Reines

Bugey

Chooz

Palo Verde

Unloaded:

KamLand

Borexino



Challenges: Stability and purity

Palo Verde:

A.G.Piepke, S.W.Moser, V.M.Novikov; NIM A 342 (1999) 392-398

Chooz:

τ ~ 240 days

Gd(NO3)3

Chooz Coll.; Eur.Phys.C27, 331-374 (2003)

KamLand Background:



Liquid scintillator properties

High energy resolution

Low energy detection threshold

high purity (Borexino)

fast signals (better understanding of timing properties)

moderate cost

Improved stability of metal loaded scintillators



Liquid scintillator future

Double Chooz, Daya Bay, Reno

SNO+

LENA,…



Liquid scintillator components

Solvent– pseudocumene, toluene, anisole– „Safe scintillators“: PXE, LAB, DIN– Admixtures: alkanes, mineral oil

Primary fluor– PPO– BPO– Butyl-PBD,…

Secondary fluor– Bis-MSB– POPOP

α, β, γ

*

PMT



Comparison solvents: Light yield

Solvent Yield (6 g/l PPO)

PC 1.00

Anisole 0.81

PXE 0.88

LAB 0.74

Dodecan 0.40

Oil 0.33

MPIK measurements M.Chen, INT Workshop 2005



Comparison solvents: Attenuation length

360 380 400 420 440 460 480 500 520 540 560

1

10

100

1000

atte

nuat

ion

leng

th [m

]

wavelength [nm]

n-Dodecan LAB o-PXE Anisole

MPIK measurements (UV/Vis, 10 cm cell)

M.Wurm (TUM), ANT 2009



Purification methods

Column purification – Radioimpurities– Optics

N2 purging

– Radon, 85Kr– Light yield (oxygen)

Water extraction– Radioimpurities (e.g. 40K)

Distillation– Radioimpurities– Optics

350 400 450 500 550 600-0,0020,0000,0020,0040,0060,0080,0100,0120,0140,016

ab

sorb

an

ce

wavelength [nm]

unpurified b1 unpurified b2 purified

10 m

320 360 400 440 480 520 560 600

0,0

0,1

0,2

0,3

0,4

0,5

abso

rban

cewavelength [nm]

not purified column purification



Purification methods

Column purification – Radioimpurities– Optics

N2 purging

– Radon, 85Kr– Light yield (oxygen)

Water extraction– Radioimpurities

Distillation– Radioimpurities– Optics

Borexino

KamLand

CTF

LAK

Solar neutrino phase



Borexino Background

PRL 101, 091302 (2008)

40K < 3 ∙10-18 g/g238U: 1.6 ± 0.1∙10-17 g/g232Th: 6.8 ± 1.5∙10-18 g/g



LAB

LAB is proposed in SNO+, Daya Bay, RENO New high light yield, transparent solvent?

– Used since decades

– Average light yield

– Average transparency It is a high flash point, low toxicity solvent at moderate

cost and reasonable optics, …but:

– Mixture

– Biphenyls (absorption/emission!)

– Timing properties

CC

CC

CC

CC

CC

CC

CC

CC

C

360 380 400 420 440 460 480 500 520 540 560

1

10

100

1000

atte

nuat

ion

leng

th [m

]

wavelength [nm]

n-Dodecan LAB o-PXE Anisole

LAB (6 g/l PPO)

PXE (6 g/l PPO)



Solvent mixtures

Advantage: Parameters tuneable optimize material compatibility change timing properties match density adjust light yield

6 g/l PPO

Light production in alkanes Radiation creates e-- - hole pairs Recombination, fragmentation, radicals, reactions excited molecules energy transfer to fluors

M.Wurm, diploma thesis, TUM(2005)

Lig

ht

yie

ld [

% s

tan

da

rd]

C.Aberle, diploma thesis, MPIK (2008)

PXE (mass fraction)

0,0 0,2 0,4 0,6 0,8 1,00

10

20

30

40

50

60

70

80

90

100

Ligh

t Yie

ld [%

of s

tand

ard

]

PXE [volume fraction]



Comparison fluors

• transparent• well established• high quantum yield

BPO

(Butyl-)PBD pTP

PPO• high(est) light yield• emission around 400 nm

• absorption properties• limited availibility

• low solubility • poor quantum yield

• fast• overlap with bis-MSB

• high light yield

• poor quantum yield• costs



Energy transfer (non-radiative)

Jk RR

FRET 6

0

LRexchange eJk /2

dJ DA f 4

)()(



Critical concentration

30

10 Rc

Critical distance R0:

Critical conc.:

50 %50 %

Energy transferPhoton emission, decay

For PPO < 1g/l in PXE, PC,…

For PPO ~ 2.1 g/l in dodecane

Donor * Acceptor

0 2 4 6 8 100

10

20

30

40

50

60

70

80

90

100

110

PXE Dodecane

Lig

ht Y

ield

[% s

tan

da

rd]

PPO concentration [g/l]



Light yield model

C.Buck, F.X. Hartmann, D.Motta. S.Schönert, CPL, 435 (2007) 252 - 256

C.Aberle, diploma thesis, MPIK Heidelberg (2008)

A

A

e

e

sq

sq

d

1

q

a

'

a

'

q

i

D*

2 D2

A

Q

Q

D1

D*

1

'

i

See poster by C.Aberle!



Timing properties

C.Aberle, Diploma thesis, MPIK Heidelberg (2008)

D.Motta (CEA Saclay): pulse shape to tag events in different detector regions

Target

Gamma Catcher candidates

Eve

nts

Time [ns]



Metal loaded scintillators

Solar neutrinos (LENS, SIREN):– Metal: Ytterbium, Indium, Gadolinium– Challenge: High loadings

Reactor (Double Chooz, Daya Bay, RENO) – Metal: Gadolinium – Challenge: Stability

ββ-decay (SNO+)– Metal: Neodymium– Challenges:

transparency; purity



Indium

Indium-loaded scintillators at LLBF > 1 year (2003/04) MPIK: In(acac)3 (F.X.Hartmann et al.)

INR/LNGS: Carboxylic acid version

> 50 g/l Indium

D. Motta, C. Buck, F. Hartmann, T. Lasserre, S. Schönert, U.Schwan, NIM A 547 (2005) 368.N.A. Danilov, C.Cattadori, A..di Vacri et al., Radiochemistry 47 (2005) 487-493.



Gadolinium (Carboxylates)

400 420 440 460 480 500 520 540 560 580 6000,000

0,005

0,010

0,015

0,020

0,025

0,030

0,035

0,040

0,045

0,050Target

5 m

Ab

sorb

an

ce

wavelength [nm]

Dec 05 Jan 06 Feb 06 Mar 06 Apr 06

0 1 2 3 4 50,0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

0,9

1,0Target

Gd-

conc

. [g/

l]

months

Double Chooz mockup (TMHA, MPIK 2003):

INR/LNGS: 2 x 1.2 t Gd-LS (0.1%) in frame of LVD

Now used in Daya Bay and RENO• Y.Ding et al., NIM A 584 (2008) 238-243.• M.Yeh et al., NIM A 578 (2007) 329-339.

arXiv:0803.1577v1 [physics.ins-det] 11

Mar 2008



Gadolinium (β-diketones)

Purified by sublimation

stability/compatibility tests > 4 y

att. length (1 g/l) > 50 m in ROI

100 kg produced

0 300 600 900 1200 1500 1800 2100 2400 2700

0,1

1

coun

ts

Energy [keV]

before sublimation after sublimation

Ge spectrum Gd(BDK)3

400 420 440 460 480 500 520 540 560 580 6000,000

0,005

0,010

0,015

0,020

0,025

0,030

2.5m

5mA

bs (

10 c

m c

ell)

wavelength [nm]

02Aug2006 30Aug2006 04Feb2009

10m



Scintillator production for Double Chooz

Scintillator production has started

Poster by F.X.Hartmann on DC scintillator chemistry



Neodymium

400 425 450 475 500 525 550 575 600 625 6500

5

10

15

20

25

mo

l.ext

.[l/(

mo

l*cm

)]

wavelength [nm]

Nd(acac)3nH

2O

NdCl3

MPIK (2003): Tests on BDK and CBX versions (F.X.Hartmann et al.)

Light yield measurements at LNGS

C.Cattadori et al., submitted to NIM A (2009)arXiv:0909.2152v1 [physics.ins-det] 11 Sep 2009



Summary

Liquid scintillators key technology for upcoming large scale neutrino detectors

Many solvent and fluor candidates

- Choice depends on application and detector characteristics

- Requirement for „safe“ scintillators (PXE, LAB,…)

Energy transfer models allow light yield predictions

Several applications for metal loaded scintillators

significant improvement in last years (stability etc.)

christian buck, mpik heidelberg

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