The Indium-loaded Liquid Scintillator (InLS)The Indium-loaded Liquid Scintillator (InLS)

Zheng Chang*, Christian Grieb and Raju S. Raghavan

Dept, of Physics, Virginia Tech, Blacksburg, VA 24061

Richard L. Hahn, Minfang Yeh and Alexander Garnov

Chemistry Dept., Brookhaven National Lab, Upton, NY 11973

Jay Benziger

Dept. of Chemical Engineering, Princeton University, Princeton, NJ 08544

Objectives

The synthesis of 125 tons of high quality indium-loaded liquid scintillator (InLS) is a key technology for the success of LENS. Stringent requirements on the InLS must be realized in the development of LENS detector:

Basic robustness and reproducibility of the chemical recipe for metal loading;

High metal loading, typically ~ 8 - 10 wt. %;

Long optical attenuation length, typically > 8 m;

High scintillation yield ~ 55% of the unloaded solvent;

Long term stability on the scale of years;

Choice of solvent vis-a-vis health/safety in an underground environment.

VT Recipe for InLS(Improved from US Patent (2004): Chandross & Raghavan, Filed 2001)

Vacuum

Evaporation

HMVA (>98%) NH4MVA + NH4OH

Stir

Add NH4OH

Equal vol.

Of the org.

Liquid-liquid extraction system

InLS: In% = 8 S% > 55 L1/e > 8 m

Equal vol.

Of the org.

Add

NH4Ac

1. Neutralization

2. On-line purification and solution preparation

3. Solvent extraction and vacuum evaporation

InCl3

Org. Waste

TBPO: Tri-n-buylphosphine oxideFluors: 5g/L PPO (2,5-Diphenyloxazole) and 15 mg/L Bis MSB (p-Bis(o-

methylstyryl)benzene)

Aq. Waste

TBPO-toluene NH4MVA

TBPO-toluene NH4MVA

Dry Solid of In(MVA)2(OH)

Dissolve in PC

Add fluors

Mix together

with H

exane InAc3 + NH4Cl

In(MVA)2(OH) in Hexane

Purification of Methylvaleric Acid (HMVA)

1) Vacuum distillation

2) When transferred into NH4MVA solution, equilibrated with 0.5% TBPO-toluene solution twice to remove any organic or inorganic impurities.

Distillation of MVA under Vacuum

-0.04

-0.02

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

400 430 460 490 520 550 580 610 640 670 700

WL (nm)

Ab

s

43

0

Distilled

Original

Lower BP fraction

Higher BP fractionion

Purification of Pseudocumene (PC)

Chromatogram Plot

File: c:\... \a_vt\gcms\gcmsdata\bzdhdinpc 03-09-05\pcaezar#1_3-8-05.smsSample: PCAezar#1 Operator: Z. ChangScan Range: 1 - 1679 Time Range: 0.00 - 27.98 min. Date: 3/8/2005 10:12 AM

5 10 15 20minutes

0

10

20

30

40

kCounts RIC all PCAezar#1_3-8-05.SMS In the PC from Sigma-Aldrich, three groups of bensaldehydes were observed at the level of 50 ppm. These impurities lower the optical transparency of PC at a wavelength of ~430 nm.

GC-MS of Pseudocumene

BZHs were found as major impurities (<100 ppm) in commercial PC by GC-MS. BZHs are produced by the oxidation of PC in the air over a long period of time. BZHs lower the optical transparency of PC. BZHs can be removed by passing PC through the alumina (Al2O3) column.

Benzaldehydes (BZH)

HexaneIn(Ac)3 (aq) + MVA- (aq) In(OH)(MVA)2 in Hexane

In(OH)(MVA)2 Solid InLS in PC

Evaporation PC

Solvent Extraction

Org. Phase (Hexane) In(OH)(RCOO)2

In3+ + OH- +2RCOO- In(OH)(RCOO)2

H+ + RCOO- RCOOH

NH3 + H2O NH4+ + OH-

In(Ac)3 In3+ + 3Ac-

… …

Aqueus Phase (Water)RCOOH: 2-methylvaleric acidPC: 1, 2, 4-trimethylbenzene

InLS• Remove Hexane

• Dissolve in PC

• Add the fluors

Solvent Evaporation

Solvent evaporation step provides many advantages, such as

to be able to select a proper solvent for the solvent extraction

to be able to select an ideal chemical as the scintillator solvent

to decrease the H2O coexisting in the indium carboxylates

In(Ac)3 (aq) + MVA- (aq) In(OH)(MVA)2 in Hexane

In(OH)(MVA)2 Solid InLS in PC

Hexane

Evaporation PC

Composition Analysis on the InLS (1)

Composition analysis were conducted on the InLS samples. The following chemical groups were measured:

InIII, MVA, (HMVA)2, NH4+, Cl-

Total-MVA/In decreases with the extraction pH.

Total-MVA/In = 2.1

HMVA was found in the form of (HMVA)2 and decreases with the extraction pH.

HMVA/In = 0.1

0.0

1.0

2.0

3.0

4.0

5.0

3.5 4 4.5 5 5.5 6 6.5 7 7.5 8

pH

To

tal-

MV

A/In

VT recipeBL recipe (BNL)BL recipe (VT)VT tests

0.0

0.5

1.0

1.5

2.0

3.5 4 4.5 5 5.5 6 6.5 7 7.5 8

pH

HM

VA

/In

VT recipeBL recipe (BNL)

Composition Analysis on the InLS (2)

OH- groups was found to maintain constant between pH 3.8 and 5.5, and to increases with the extraction pH.

OH-/In = 1.0

H2O/In was found to decrease with the extraction pH by the VT recipe.

H2O/In = 0.6

The empirical formula for the indium carboxylate at pH 6.88:

In(OH)1(MVA)2

0.0

0.5

1.0

1.5

2.0

3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0

pH

H2O

/In

VT recipeBL recipe (BNL)

0.0

0.5

1.0

1.5

2.0

2.5

3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0pH

OH

- /In

VT recipeBL recipe (BNL)

The InLS samples were studied by electrospray mass spectrometry over time. Indium oligomers were found to grow in amount and types as pH > 7. As pH < 7, less OH- groups are present in the carboxylates, and the oligomerization process becomes insignificant.

In In

InInMVA

MVA

MVA

MVAOHMVA

MVA

MVA

MVA O

HO+

+ H2O

Speciation of the Indium Complexes

ZVT45 PC #24 RT: 0.47 AV: 1 NL: 6.53E5T: + c Q1MS [ 50.00-1200.00]

100 200 300 400 500 600 700 800 900 1000 1100 1200m/z

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

75

80

85

90

95

100

Rel

ativ

e A

bund

ance

120.0581

251.1692

219.1216

zVt45 (pH 6.88, S=54%, d=0.97 g/ml). Abs@430nm = 0.003 (10-06-05), MS Spectrum obtained on 11-11-05)

Mass Spectrometry of the InLS

PC Desired Species of indium complex

PHYLOWCON2 #45 RT: 1.27 AV:1 NL: 8.71E6T: + p Q1MS [ 50.00-1500.00]

100 200 300 400 500 600 700 800 900 1000 1100 1200 1300 1400 1500m/z

05

101520253035404550556065707580859095

100

Re

lativ

e A

bun

danc

e

83.1100

219.2600

121.1200

255.3100 739.3600637.3300 1096.4200

550.4300272.1800 391.3200

zVt45 (pH 6.88, S=54%, d=0.97 g/ml). Abs@430nm = 0.004 (03-22-06), MS Spectrum obtained on 03-29-06)

PC

Additional species growing with time

The scintillation yield (S) is mainly affected by the content of the organic acid in the InLS. The chemical speciation of the indium carboxylates does not affect the S% significantly.

For Typical Samples

At In-loading > 8 wt. %

S = 55 - 65%Light Yield of Some VT Samples with In > 8%

1.E+00

1.E+01

1.E+02

1.E+03

1.E+04

1.E+05

1.E+06

0 100 200 300 400 500

Channel

Coun

tsPseudocumene

zVt38, S=61%

zVt45, S=56%

Cs-137Sample vial

PM

T

High voltage Signa

l

Ground

Photon yield

Scintillation Yield

Scintillation Light Yield

Optical Attenuation Length (L1/e)

UV/Vis absorbance of zVt45 (pH 6.88) with time

-0.01

0

0.01

0.02

0.03

0.04

0.05

350 390 430 470 510 550 590 630 670l (nm)

No

rmal

ized

Ab

sorb

ance

10/06/05

01/23/06

03/22/06

05/31/06

8.6 m after 8 months

Transparency of InLS

The optical attenuation length (L1/e) is very sensitive to the chemical species and trace impurities in the InLS. Both the organic impurities and the oligomers of the indium carboxylates absorb the light at wavelength of ~ 430 nm.

For Typical Samples

In-loading = 8.2 wt. %

L1/e >> 10 m at the prep.

L1/e = 8.6 m after 8 m (@430nm)

Sample pH In% S%Abs@430nm at different time

Begin 1 Mon 3 Mon 5 Mon 8 Mon 9 Mon

zVt39 7.24 8.7 64 0.001 0.002 0.003 0.009 0.012 0.013

zVt40 7.22 8.4 63 0.001 0.003 0.005 0.006 0.010 --

zVt41 7.09 8.4 59 0.003  -- --   0.008 0.009 --

zVt46 6.98 8.5 58 0.002  --  --  0.007 0.008 --

zVt38 6.94 8.3 61 0.002 0.003 0.005 0.005 0.006 0.007

zVt47 6.92 8.0 59 0.0025  -- 0.005 --  0.006 --

zVt45 6.88 8.2 56 0.003 0.004 0.005 0.005 0.005 --

zVt44 6.86 8.6 56 0.003 0.004  0.004   0.004 0.005 --

Long Term Stability of L1/e of InLS

The S values of the samples were found not to change with time. The L1/e of the samples synthesized at pH 6.88 were found to stabilize in 3

months, and their L1/e have stayed > 8 m for 8 months.

Optimum value for the extraction pH ~6.88

A new synthesis procedure, VT recipe, has been developed on the basis of previous experiments. This procedure has two special features: liquid-liquid extraction with high concentration of NH4Ac and vacuum evaporation to get solid indium carboxylates. The final InLS can be made in a desired scintillation solvent (e.g. PC) at the desired indium concentration.

With the VT recipe, we have achieved:

Low content of H2O and acid and long-term stability;

High scintillation yield (S > 55%);

Long attenuation length (L1/e > 8 m at 430 nm);

L1/e has been stable for > 8 months.

Achievements

OligamerizationPhase

Distribution

In(III) Species in the Solvent Extraction

In(Ac)3

In(MVA)2+ In(OH)2

+

In(MVA)2+ In(MVA)(OH)+

In(OH)2+

In(MVA)3 In(MVA)2(OH)

In(MVA)(OH)2

In(OH)3

In(MVA)4-

In(MVA)3(OH)- In(MVA)2(OH)2

- In(MVA)(OH)3

- In(OH)4-

(Aq.) (Org.)

In(MVA)3 In(MVA)2(OH)In(MVA)(OH)2

In(OH)3 (?)

In2(MVA)6 In2(MVA)4(OH)2

In2(MVA)2(OH)4

In2(OH)6 (?)

zyxnm

mnxyzmnxyz

zyxnm

mnxyzmnxyz

zyxnm

mnxyzmnxyz

zyxnm

mnxyzmnxyzpdmp

zyxnm

mnxyzmnxyz

orgzxnmaqaqaqaq

zC

yC

nC

yxKKKC

mC

zxyxnm

]OH[]HMV[]MV[]NH[]In[

]OH[]HMV[]MV[]NH[]In[

]OH[]HMV[]MV[]NH[]In[

]OH[]HMV[]MV[]NH[]In[)(])HMV[(2]HMV[

]OH[]HMV[]MV[]NH[]In[]In[

O)(H(HMV))(MV)(NHIn OH )H( MV NH In

243

H2O

243

H

243

NH4

2432

HMVA

2433

In

2y-

42-

43

Speciation Study In the Future

A speciation study should be conducted in the future to get a comprehensive understanding of the solvent extraction and the oligomerization processes. This knowledge is vital to the design of the large-scale synthesis and to the improvement of the long-term optical stability.

Study the thermodynamic parameters of the VT process. Monitor long term behavior and optimize recipe

Determine practical quality control parameters for large scale commercial production

Engineering transition from 100 ml production scale to 10-100 L scale for MINILENS (needs 200 L)

OUTLOOK