SNO+ scintillator
purification and assay
Richard Ford
SNOLAB
LRT2010, Sudbury, Canada
August 29, 2010
The SNO+ Experiment
860 tonnes scintillator
1000
tonnes
D2O
(LAB
+ 2g/L
PPO)
Support Structure
for 9500 PMTs
12 m Diameter
Acrylic Vessel
Scintillator purification
Rope net anchored to
the cavity floor
1700 tonnes Inner
Shielding H2O
5300 tonnes Outer
Shield H2O
Urylon Liner and
Radon Seal
Richard Ford (SNOLAB)
LRT2010, Sudbury
SNO+ Physics Program (2 phases)
 Neutrino-less double beta decay (Nd loaded)
 Determine if neutrino is Dirac or Majoranna type
 Most sensitive measurement of absolute neutrino mass
 Neutrino physics
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Solar neutrinos (pep, CNO)
Geo antineutrinos
Reactor antineutrinos
Supernova neutrinos
Richard Ford (SNOLAB)
LRT2010, Sudbury
SNO+ in SNOLAB
Isolated
9’ ventilation
6600L
SNOLAB
Excavationraise
PhasetoII:
(Isolated
path to surface)
Cryopit vent
cavity
SNOLAB Excavation Phase I:
Cube Hall and Ladder Lab
Scintillator
purification
Existing
Water plant
SNO Facility
Rail-car unloading
terminal
New personnel
SNO+
control room
facilities
Storage tanks
SNO+
detector
Richard Ford (SNOLAB)
LRT2010, Sudbury
Scintillator based on LAB
 Linear alkylbenzene (LAB) identified as the liquid scintillator
solvent:
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Chemical compatibility with acrylic
High light yield
High purity available
Safe
 Low toxicity
 High flash point 140°C
 Boiling point 278-314°C
 Environmentally safe
 Low solubility in water 0.041 mg/L
Inexpensive
Suitable density r = 0.86 g/cm3
Petresa Plant – Bécancour, QC
Richard Ford (SNOLAB)
LRT2010, Sudbury
SNO+ signal and backgrounds
Zero-neutrino double beta with Nd
56 kg of 150Nd and <mn> = 100 meV
3-year pep and CNO solar neutrino
signals
- Backgrounds at Borexino levels: U and Th ~10-17 g/g, and K 10-18 g/g
Richard Ford (SNOLAB)
LRT2010, Sudbury
Purification strategies:
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Multi-stage distillation
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Pre-purification of PPO concentrated solution
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Removes Rn, O2 and provides LAB humidity control
Water extraction (liquid-liquid extraction)
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pH controlled precipitation (self-scavenge) for Nd salt solution
Thin-film evaporation of THMA
Steam/N2 stripping under vacuum
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N2 sparging, water extraction, and distillation
Pre-purification of Nd salt and TMHA
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Initial LAB cleanup for high radio-purity and optical clarity
Dual-stream PPO distillation for scintillator recirculation
Provides high-flow recirculation polishing stage
Effective for ionic metals (K, Pb, Ra) and limited efficiency for Th and Po
Stable for PPO and Nd-LAB solutions
Functional metal scavengers
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High-flow columns effective for Pb, Bi and Ra
Can be regenerated with acid wash
Processing and assay of the acid wash provides a method for radio-assay of scintillator
Richard Ford (SNOLAB)
LRT2010, Sudbury
Production of Ra and Pb Spikes in LAB
Metals are not soluble in LAB, so we seek to produce “natural” radioactive
spikes that are similar to the way that real contaminations will occur.
Ra spike from 228Th
In vacuum 224Ra with 96 KeV recoil
can reach and implant into LAB.
Flask cooled in dry ice to prevent
condensation on source.
Vacuum flask
P < 1 mBar
228Th
salt acid solution is
absorbed by Dowex resin in
a Teflon column
Peristaltic
air pump
90 Bq 228Th
evaporated
on SS plate
above LAB
Washing flask
with LAB
Pb spike from 228Th
Radon emanation from the column is
purged with air and through fine frit
bubbled through LAB. Radon decays in
LAB, with 212Pb recoiling into LAB.
Richard Ford (SNOLAB)
LRT2010, Sudbury
Laboratory LAB batch distillation tests
- Fractional batch distillation
- 70 mTorr vacuum
- 100°C
- Improved UV transmission
- Distillation effective for removal
of heavy metals (Th, Pb, Po, Bi)
Richard Ford (SNOLAB)
LRT2010, Sudbury
Dual-Stream Fractional Vacuum Distillation
Dual stream allows online distillation of
scintillator (LAB + PPO).
Reflux
Tower
LAB or
Scintillator
Condenser
Vacuum pump
55 Torr
238°C
Mix
Reboiler
20 Torr
242°C
PPO
solution
Vac pump
Kettle
(LAB flashs and PPO boils)
Bottoms
Richard Ford (SNOLAB)
LRT2010, Sudbury
Scintillator
output
Effectiveness depends
on design (number of
stages, reflux rate,
bottoms concentration,
vacuum level and
stripping).
Borexino purification skids
The distillation tower is similar
size to that designed for SNO+.
Condenser
Distillation tower
Reboiler
SNO+ tower will be 32” dia x 15’ H.
>99% removal efficiency for heavy
metals at 20 LPM flow (1000kg/hr).
Richard Ford (SNOLAB)
LRT2010, Sudbury
Liquid-liquid extraction purification
(water extraction of solvent)
Output Activity of 212Pb in LAB and water
0
10
LAB
Water
• Tests with 224Ra show a high removal efficiency 98%.
• There is a lead component in LAB, irremovable by LLE.
• However, Pb and Ra removal efficiency is greatly
reduced with Nd-loaded scintillator. Maybe the excess
TMHA sequesters the Pb and Ra. Tests continue.
Output Activity of
224
Ra in Water and LAB
A, Bq/mL
• LLE efficiency of 212Pb removal from LAB is 87%.
-1
10
-2
10
0
input LAB A0 = 2.2 Bq/mL
100
200
time, min
Water
LAB
0
A, mBq/mL
10
-1
10
input LAB A0=14 mBq/mL
0
20
40
60
80
100
time, min
Richard Ford (SNOLAB)
LRT2010, Sudbury
300
400
Counter-current water extraction
Scintillator
output
Packed column
Water purification
(integrated with the SNO
high-purity RO system)
50 psig
80°C
Scintillator
input
Richard Ford (SNOLAB)
LRT2010, Sudbury
SCHEIBEL® Column
for liquid-liquid extraction
SNO+ column is 30” dia x 23’ H.
Flow 150 LPM, with 4 equilibrium stages.
www.modularprocess.com
Richard Ford (SNOLAB)
KARR® and SCHEIBEL® are registered trademarks of Koch-Glitsch, LP.
LRT2010, Sudbury
Gas stripping
Scintillator
input
Vacuum pump
to vapour recovery
and vent header
Packed column
150 Torr
100°C
SNO+ column is 24” dia x
24’ H. Flow 150 LPM.
- 95% Rn removal eff.
- 99% O2 removal eff.
Steam generator
N2
Scintillator
output
Richard Ford (SNOLAB)
LRT2010, Sudbury
QuadraPureTM Metal Scavenger
- QuadrapureTM metal scavengers are functionalized macro-porous polystyrenebased resin beads (~500 um) for extraction of metal contaminants.
- In flow tests with spikes, high extraction efficiencies are obtained even at high flow
rates, up to 150 bed volumes per hour (depends also on column dimensions).
- Beads can be stripped with HCL acid and regenerated with methanol.
Richard Ford (SNOLAB)
LRT2010, Sudbury
SNO+ scavenger columns
SNO+ columns 6” dia x 200” H.
Six columns for flow 150 LPM.
Richard Ford (SNOLAB)
LRT2010, Sudbury
~ 800 Tonnes LAB Scintillator
Extraction
QuadraPure scavenger columns
MeOH regeneration
100 L 0.1M HCl
Elution
Surface laboratory
30.0 g Dowex 5WX8 resin
100 ml 0.25M EDTA (pH 10)
Secondary
Concentration
HTiO co-precipitation
1.5 ml conc. HCl
- delayed coincidence
Counting
liquid scintillation counter
Richard Ford (SNOLAB)
LRT2010, Sudbury
Adapted from SNO technology
Underground plant
Method for radio-assay of scintillator
Scintillator plants
Richard Ford (SNOLAB)
Status: The plants have been designed and a
process hazard review has been completed.
The columns, vessels, HXs, and equipment is
specified and currently being quoted for
fabricated.
LRT2010, Sudbury
Specifications
 Materials – SS316, Teflon, glass, acrylic
 Pressure – max pressure of any pump + 50% (so that burst disk is not
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close to operating range) ~ 150psi.
Temperature – 350°C (just over BP at 18psi)
Surface preparations and cleanliness – Electropolished. Final cleaning
to Mil spec 1241 class 50. Oxygen service specification generally okay
Leak tightness – 10-9 mbar.L/sec fittings, 10-8 for vessels.
Pumps, valves and fittings:
- 1”-2” SS electro-polished tubing, fusion welded
- VCR fittings (<=1”)
- Metal gaskets (eg. Helicoflex) for >1”
- O-rings Teflon Encapsulated Viton (TEV)
- Diaphragm or bellows valves for leak tightness
- Mag-drive pumps
Insulation to TSSA and INCO standard for underground
Codes (electrical CSA, pressure vessel TSSA, …)
Richard Ford (SNOLAB)
LRT2010, Sudbury
SNO+ Process Interconnection System
SNO+ Operating Modes
• LAB receiving and purification
• PPO concentrate mix and purification
• Nd(RCOO)3 concentrate loading and purification
• Scintillator Mixing, stripping, and filling the AV
• On-line purification and assay (SNO+ Nd phase)
• Removal of Nd(RCOO)3
• On-line purification and assay (SNO+ SN phase)
• Unloading AV and shipping LAB
Richard Ford (SNOLAB)
LRT2010, Sudbury
AV Fill (PPO from storage)
Richard Ford (SNOLAB)
LRT2010, Sudbury
Conclusions
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SNO+ will requires extremely low levels of high-energy beta and gamma-ray background
activities from 214Bi, 212Bi, and 210Bi, all from the 238U and 232Th chains, and also
40K.
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We have investigated LAB scintillator purification methods for the purpose of designing
the SNO+ purification and loading/unloading plants.
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We have developed methods to make “natural” spikes of 212Pb and 224Ra using recoil
implantation techniques from a 228Th source, for the purpose of testing purification
methods.
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Distillation is a well known reliable technique for the initial purification of the LAB and
PPO, however the flow rate is low due to the size and heat and cooling requirements.
We have designed the SNO+ plant “dual-stream” so that the scintillator can be distilled
and remixed in recirculation mode.
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Water liquid-liquid extraction is effective for ionic metals (K, Pb, Ra), and will will a good
method for high-flow “polishing” recirculation of the scintillator. It is stable with Nd-LAB,
but maybe not very effective due to TMHA.
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Functional method scavengers are effective in high-flow columns for removal of Pb and
Ra (and maybe Th and Po). More testing to show stability with Nd-LAB is on-going. The
functional groups can be stripped and regenerated, with recovery and processing of the
acid providing a radio-purity assay method.
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The SNO+ purification and liquid handling plants have been designed partly on the basis
of these tests, and partly on the basis of column efficiency silulations and the experience
of Borexino.
Richard Ford (SNOLAB)
LRT2010, Sudbury
SNO+ H2O Simplified Process Flow Block Diagram
INCO water
VE-02
10-Tonne
Primary
RO
Zeolite
Softener
Filter &
deaeorate
PDG
P-15
185
New
H2O RO
HTiO
IX
UV
254
P-11
HX-01
F-06
HX-02
New RO commissioned 2006
Jan-08: New water plant additions
to provide AV fill and recirculation
SNO+ Cavity
Richard Ford (SNOLAB)
LRT2010, Sudbury