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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

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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
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.


1. Neutralization

Add NH4OH

HMVA (>98%)

NH4MVA + NH4OH

2. On-line purification and solution preparation

Equal vol.

Of the org.

Equal vol.

Of the org.

TBPO-toluene NH4MVA

TBPO-toluene NH4MVA

Mix together with Hexane

Org. Waste

Add

NH4Ac

InAc3 + NH4Cl

InCl3

3. Solvent extraction and vacuum evaporation

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

Liquid-liquid extraction system

Stir

In(MVA)2(OH) in Hexane

Vacuum

Evaporation

Dry Solid of In(MVA)2(OH)

Dissolve in PC

Add fluors

Aq. Waste

TBPO: Tri-n-buylphosphine oxide

Fluors: 5g/L PPO (2,5-Diphenyloxazole)

and 15 mg/L Bis MSB (p-Bis(o-methylstyryl)benzene)

VT Recipe for InLS

(Improved from US Patent (2004): Chandross & Raghavan, Filed 2001)


Purification of Methylvaleric Acid (HMVA)

  • Vacuum distillation

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


GC-MS of

Pseudocumene

Purification of Pseudocumene (PC)

Benzaldehydes (BZH)

  • 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.


Solvent extraction

Hexane were observed at the level of 50 ppm. These impurities lower the optical transparency of PC at a wavelength of ~430 nm.

In(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

InLS

  • Remove Hexane

  • Dissolve in PC

  • Add the fluors

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 acid

PC: 1, 2, 4-trimethylbenzene


Solvent evaporation

Hexane were observed at the level of 50 ppm. These impurities lower the optical transparency of PC at a wavelength of ~430 nm.

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

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

Evaporation

PC

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


Composition analysis on the inls 1

Composition Analysis on the InLS (1) were observed at the level of 50 ppm. These impurities lower the optical transparency of PC at a wavelength of ~430 nm.

  • 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


Composition Analysis on the InLS (2) were observed at the level of 50 ppm. These impurities lower the optical transparency of PC at a wavelength of ~430 nm.

  • 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


PHYLOWCON2 were observed at the level of 50 ppm. These impurities lower the optical transparency of PC at a wavelength of ~430 nm.

#

45

RT:

1.27

AV:

1

NL:

8.71E6

T:

+ p Q1MS [ 50.00-1500.00]

83.1100

100

95

MVA

HO

MVA

OH

In

90

In

+

MVA

MVA

85

MVA

O

MVA

80

+ H2O

In

In

MVA

MVA

75

219.2600

Relative Abundance

70

65

121.1200

60

Additional species growing with time

55

PC

50

45

40

35

30

25

20

255.3100

15

739.3600

637.3300

1096.4200

10

550.4300

272.1800

391.3200

5

0

100

200

300

400

500

600

700

800

900

1000

1100

1200

1300

1400

1500

m/z

zVt45 (pH 6.88, S=54%, d=0.97 g/ml). [email protected] = 0.003 (10-06-05), MS Spectrum obtained on 11-11-05)

Mass Spectrometry of the InLS

120.0581

PC

Desired Species of indium complex

251.1692

219.1216

zVt45 (pH 6.88, S=54%, d=0.97 g/ml). [email protected] = 0.004 (03-22-06), MS Spectrum obtained on 03-29-06)

ZVT45 PC

#

24

RT:

0.47

AV:

1

NL:

6.53E5

T:

+ c Q1MS [ 50.00-1200.00]

100

95

90

85

80

75

70

65

60

55

50

Relative Abundance

45

40

35

30

25

20

15

10

5

0

100

200

300

400

500

600

700

800

900

1000

1100

1200

m/z

Speciation of the Indium Complexes

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.


Cs-137 were observed at the level of 50 ppm. These impurities lower the optical transparency of PC at a wavelength of ~430 nm.

Sample vial

Ground

PMT

Scintillation Yield

High voltage

Photon yield

Signal

Scintillation Light Yield

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%


Optical attenuation length l 1 e

Transparency of InLS were observed at the level of 50 ppm. These impurities lower the optical transparency of PC at a wavelength of ~430 nm.

8.6 m after 8 months

Optical Attenuation Length (L1/e)

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)


Long Term Stability of were observed at the level of 50 ppm. These impurities lower the optical transparency of PC at a wavelength of ~430 nm. 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


Achievements were observed at the level of 50 ppm. These impurities lower the optical transparency of PC at a wavelength of ~430 nm.

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.


In iii species in the solvent extraction
In(III) Species in the Solvent Extraction were observed at the level of 50 ppm. These impurities lower the optical transparency of PC at a wavelength of ~430 nm.

(Aq.) (Org.)

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-

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 (?)

Phase Distribution

Oligamerization


Speciation study in the future
Speciation Study In the Future were observed at the level of 50 ppm. These impurities lower the optical transparency of PC at a wavelength of ~430 nm.

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.


OUTLOOK were observed at the level of 50 ppm. These impurities lower the optical transparency of PC at a wavelength of ~430 nm.

  • 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)


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