1. SNOLAB Workshop VIII, Sudbury, August 26-28, 2009 Design Overview One year ago Progress –Personnel –Pb blocks –Structural design –Siting / Installation –On-going simulation work –Near-term activities HALO - a Helium and Lead Observatory Progress Report C.J. Virtue

2. SNOLAB Workshop VIII, Sudbury, August 26-28, 2009 Philosophy - to produce a –Very low cost –Low maintenance –Low impact in terms of lab resources (space) –Long-term, high livetime dedicated supernova detector HALO - Design Overview “Helium” – because of the availability of the 3 He neutron detectors from SNO + “Lead” – because of high ν -Pb cross-sections, low n-capture cross-sections, sensitivity to ν e (dominantly) and ν x complementing water Cerenkov and liquid scintillator detectors

3. SNOLAB Workshop VIII, Sudbury, August 26-28, 2009 HALO-I - Design Overview Lead Array –32 three meter long columns of annular Lead blocks – 76 tonnes total lead mass (864 blocks) Neutron detectors –Four 3 meter 3 He detectors per column –384 meters total length Moderator –~250mm Ø schedule 40 PP tubing Reflector and Shielding –~15 cm thick graphite blocks –1’ of water (boxes) on 5 sides

4. SNOLAB Workshop VIII, Sudbury, August 26-28, 2009 In 76 tonnes of lead for a SN @ 10kpc †, MSW oscillated –Assuming FD distribution around T=8 MeV for ν μ ’s, ν τ ’s. –65 neutrons through ν e charged current channels 29 single neutrons 18 double neutrons (36 total) –20 neutrons through ν x neutral current channels 8 single neutrons 6 double neutrons (12 total) ~ 85 neutrons liberated; ie. 1.1 n/tonne †- Engel, McLaughlin, Volpe, Phys. Rev. D 67, 013005 (2003) HALO - SN neutrino signal – Phase 1

5. SNOLAB Workshop VIII, Sudbury, August 26-28, 2009 Summary of status one year ago NSERC funding in place Pb blocks in storage in warehouse in Sudbury Lead carbonate powder present on many blocks Decision taken to paint blocks; search for paint in progress Conceptual design established Block stacking options under consideration Mechanical creep test jig in fabrication SNGEN code being modified to simulate HALO

6. SNOLAB Workshop VIII, Sudbury, August 26-28, 2009 Progress - Personnel C. Virtue (50%) S. Yen (25%) T. Shantz (100%) HALO MSc student – HALO design / construction S. Korte (10%) SNO+ MSc student – SN simulation (defense yesterday) J. Farine (10% ) F. Duncan (5%) A. Habig K. Scholberg A. Hime R.G.H. Robertson J.F. Wilkerson C. Duba M. Schumaker (50%) HALO / SNO+ postdoc C. Kraus (TBD) K. Zuber new since last year (xx%) shown for Canadian collaborators / applicants

7. SNOLAB Workshop VIII, Sudbury, August 26-28, 2009 Progress – Pb blocks Candidate paints were evaluated based on: –ASTM D 3359-08 – “Measuring Adhesion by Tape Test” results –Counting of 1 liter samples in SNOLAB low level counter –Specific gravity and immiscibility in water (suitability for application of paint by lowering the Pb blocks through a layer of paint floating on water)  resulted in paint selection

8. SNOLAB Workshop VIII, Sudbury, August 26-28, 2009 Progress – Pb blocks Between April 27 th and June 5 th 49 pallets of Pb blocks were transported to site, painted and prepared for UG transport (to occur next week)

9. SNOLAB Workshop VIII, Sudbury, August 26-28, 2009 Progress – Pb blocks Each painted block was numbered and measured Measurements fed into structural design

10. SNOLAB Workshop VIII, Sudbury, August 26-28, 2009 Progress – Pb blocks Elemental analysis (ICP-MS) done on selected paint To assess high neutron capture cross-section contaminants being built in the detector Radioactivity assessed through direct counting For potential inclusion in the Monte Carlo simulation

11. SNOLAB Workshop VIII, Sudbury, August 26-28, 2009 Superstructure drawing package is complete and under review; release for fabrication is imminent Progress - Structural Design

12. SNOLAB Workshop VIII, Sudbury, August 26-28, 2009 Progress - Structural Design Residual structural concerns… creep in Pb 1 tonne load

13. SNOLAB Workshop VIII, Sudbury, August 26-28, 2009 Progress - Structural Design Generic Creep-Rupture curve with exaggerated times to properly display the three stages. Secondary Creep Tertiary Creep Primary Creep Data from our compression jig.

14. SNOLAB Workshop VIII, Sudbury, August 26-28, 2009 Progress - Structural Design Creep test conclusions to date –Creep seen was much too large over time intervals that were very short compared to the desired detector lifetime –Design of compression jig however was unrealistic as pressure is more distributed –More realistic pressure distributions gave a large improvement but still creep was still easily detected over short times (2 weeks) –Some form of reinforcement on the Pb blocks on the bottom 4 layers of the detector will be necessary Actions to complete creep measurement program –Design of steel supporting ring for insertion in Pb blocks – done –Fabrication of sample ring – done, received Tuesday –Repeat of creep tests, with improved geometry for load spreading, with and without supporting ring – critical path for assembly  starting this evening

15. SNOLAB Workshop VIII, Sudbury, August 26-28, 2009 Progress – Siting / Installation Preferred location is the phase 3 stub Otherwise the cube hall utility drift

16. SNOLAB Workshop VIII, Sudbury, August 26-28, 2009 Progress – Siting / Installation Space is tight in phase 3 stub but adequate if 1’ of water shielding is sufficient Criteria was that background rate of neutrons seen by NCD counters be such that a SNEWS trigger with sensitivity to 20kpc would have a random coincidence rate of order once per month Achieved if rate < 0.15 Hz

17. SNOLAB Workshop VIII, Sudbury, August 26-28, 2009 Progress – Siting / Installation 1’ of water should be adequate  phase 3 stub OK ?

18. SNOLAB Workshop VIII, Sudbury, August 26-28, 2009 Progress – Siting / Installation Assembly procedure thought through Gantry crane, required for installation, delivered last week

19. SNOLAB Workshop VIII, Sudbury, August 26-28, 2009 Progress – On-going simulation work Optimization of graphite reflector thickness Optimization of moderator (PE) geometry surrounding the NCDs –Integrated with NCD mechanical support and installation / handling design Definition of calibration system Physics extraction studies

20. SNOLAB Workshop VIII, Sudbury, August 26-28, 2009 Near-term activities Transport of Pb blocks underground Fabrication of steel superstructure Assembly of Pb array (without reflector for time being) Relocation of NCDs from SNO control room to new storage shelves in phase III stub Relocation of NCD electronics from SNO control room and deck to phase III stub Collaboration meeting – Dec. 8-9 2009 Selection of particular NCDs for installation in HALO Finalize design of NCD moderator / support structure  fabrication and installation Re-establish read-out and DAQ  run