1. SNO+ scintillator purification and assay
Richard Ford
SNOLAB
LRT2010, Sudbury, Canada
August 29, 2010

2. Rope net anchored to the cavity floor
The SNO+ Experiment
860 tonnes scintillator
(LAB + 2g/L PPO)
1000 tonnes D2O
Support Structure for 9500 PMTs
12 m Diameter Acrylic Vessel
Scintillator purification
1700 tonnes Inner
Shielding H2O
Rope net anchored to the cavity floor
5300 tonnes Outer
Shield H2O
Urylon Liner and
Radon Seal
Richard Ford (SNOLAB) LRT2010, Sudbury

3. 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
Solar neutrinos (pep, CNO)
Geo antineutrinos
Reactor antineutrinos
Supernova neutrinos
Richard Ford (SNOLAB) LRT2010, Sudbury 3

4. SNO+ in SNOLAB Existing SNO Facility New personnel facilities
Isolated 9’ ventilation raise to 6600L
(Isolated vent path to surface)
SNOLAB Excavation Phase II:
Cryopit cavity
SNOLAB Excavation Phase I:
Cube Hall and Ladder Lab
Scintillator
purification
Existing
SNO Facility
Water plant
Rail-car unloading
terminal
New personnel
facilities
SNO+
control room
Storage tanks
SNO+
detector
Richard Ford (SNOLAB) LRT2010, Sudbury

5. Scintillator based on LAB
Linear alkylbenzene (LAB) identified as the liquid scintillator solvent:
Chemical compatibility with acrylic
High light yield
High purity available
Safe
Low toxicity
High flash point 140°C
Boiling point °C
Environmentally safe
Low solubility in water mg/L
Inexpensive
Suitable density r = 0.86 g/cm3
Petresa Plant – Bécancour, QC
Richard Ford (SNOLAB) LRT2010, Sudbury

6. 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 g/g
Richard Ford (SNOLAB) LRT2010, Sudbury

7. Purification strategies:
Multi-stage distillation
Initial LAB cleanup for high radio-purity and optical clarity
Dual-stream PPO distillation for scintillator recirculation
Pre-purification of PPO concentrated solution
N2 sparging, water extraction, and distillation
Pre-purification of Nd salt and TMHA
pH controlled precipitation (self-scavenge) for Nd salt solution
Thin-film evaporation of THMA
Steam/N2 stripping under vacuum
Removes Rn, O2 and provides LAB humidity control
Water extraction (liquid-liquid extraction)
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
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

8. 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.
Peristaltic
air pump
Washing flask
with LAB
228Th salt acid solution is absorbed by Dowex resin in a Teflon column
Vacuum flask
P < 1 mBar
90 Bq 228Th evaporated
on SS plate above 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

9. 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

10. Dual-Stream Fractional Vacuum Distillation
Dual stream allows on-line distillation of scintillator (LAB + PPO).
Reflux
Condenser
Tower
Vacuum pump
LAB or
Scintillator
55 Torr
238°C
Scintillator
output
Mix
Reboiler
Effectiveness depends on design (number of stages, reflux rate, bottoms concentration, vacuum level and stripping).
20 Torr
242°C
PPO
solution
Vac pump
Kettle
(LAB flashs and PPO boils)
Bottoms
Richard Ford (SNOLAB) LRT2010, Sudbury

11. 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

12. Liquid-liquid extraction purification (water extraction of solvent)
LLE efficiency of 212Pb removal from LAB is 87%.
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.
Richard Ford (SNOLAB) LRT2010, Sudbury

13. Counter-current water extraction
Water purification
(integrated with the SNO high-purity RO system)
Scintillator
input
output
Packed column
50 psig
80°C
Richard Ford (SNOLAB) LRT2010, Sudbury

14. for liquid-liquid extraction
SCHEIBEL® Column
for liquid-liquid extraction
SNO+ column is 30” dia x 23’ H.
Flow 150 LPM, with 4 equilibrium stages.
KARR® and SCHEIBEL® are registered trademarks of Koch-Glitsch, LP.
Richard Ford (SNOLAB) LRT2010, Sudbury

15. N2 Gas stripping Scintillator output input Steam generator
Packed column
150 Torr
100°C
Vacuum pump
to vapour recovery and vent header
SNO+ column is 24” dia x 24’ H. Flow 150 LPM.
95% Rn removal eff.
99% O2 removal eff.
Richard Ford (SNOLAB) LRT2010, Sudbury

16. QuadraPureTM Metal Scavenger
QuadrapureTM metal scavengers are functionalized macro-porous polystyrene-based 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

17. SNO+ scavenger columns
SNO+ columns 6” dia x 200” H.
Six columns for flow 150 LPM.
Richard Ford (SNOLAB) LRT2010, Sudbury

18. Method for radio-assay of scintillator
- delayed coincidence liquid scintillation counter
Secondary
Concentration
Elution
~ 800 Tonnes LAB Scintillator
QuadraPure scavenger columns
100 L 0.1M HCl
100 ml 0.25M EDTA (pH 10)
30.0 g Dowex 5WX8 resin
HTiO co-precipitation
1.5 ml conc. HCl
Extraction
Counting
Underground plant
MeOH regeneration
Surface laboratory
Adapted from SNO technology
Richard Ford (SNOLAB) LRT2010, Sudbury

19. Scintillator plants
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.
Richard Ford (SNOLAB) LRT2010, Sudbury

20. Specifications Materials – SS316, Teflon, glass, acrylic
Pressure – max pressure of any pump + 50% (so that burst disk is not 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

21. 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

22. AV Fill (PPO from storage)
Richard Ford (SNOLAB) LRT2010, Sudbury

23. Conclusions
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.
We have investigated LAB scintillator purification methods for the purpose of designing the SNO+ purification and loading/unloading plants.
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.
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.
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.
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.
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

24. SNO+ H2O Simplified Process Flow Block Diagram
INCO water
Filter &
deaeorate
Primary RO
VE-02
10-Tonne
PDG
Zeolite
Softener
P-15 IX
185 UV
New
H2O RO
HTiO
254
HX-01
P-11
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