the indium-loaded liquid scintillator (inls) zheng chang*, christian grieb and raju s. raghavan...
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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
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 (?)
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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