R.Svoboda, U.C. Davis /LLNL This work was performed under the auspices of the U.S. Department of Energy by University of California, Lawrence Livermore National Laboratory under Contract W-7405-Eng-48.

Improved neutron detection antineutrino tagging (Super-K, SONGS) active neutron shield (LUX) national security (LLNL Portal Monitoring Project) Improved light collection antineutrino spectral measurements reduce required PMT coverage Unwanted additives what makes good water go bad?

Pros and Cons 3 Viable: GdCl 3 relatively inexpensive Small concentrations of Gd in water improve neutron capture significantly Gd capture signature (8 MeV γ- cascade) easily detectable Workable? What is GdCl 3 effect on transparency? What are the physical effects of GdCl 3 caused by extended exposure to SK detector components? Optimal?

Injection and Measurement Optics Storage tank PMT tank Deionizing Filtering Sterilization Alignment mirror Nitrogen purge and relief valve Nitrogen purge Recirculation pump drain mixing tank and pump Light transmission arm Baffled joints 4

LLNL Test Set-Up 5

Light transmission arm Acrylic window reflected beam integrator primary beam integrator beam splitter PMT PMT light integrator Lawrence Livermore National Laboratory 9.54 meters Not shown: collamators, baffles, filters LLNL Test Set-Up N 2 Laser w/ dye attachement

primary reflected ns V Typical Waveform for 337nm 7

By putting filters of known transmittance (<1% uncertainty) into the injected primary beam, the system is seen to be linear to within 2% over a 40% variation in transmission The system is also stable to variations in PMT gain to better than 1%

Stopped recirc +/- 2% pure water fall off in transparency over time (337 nm) 0.9 %/day Preliminary Stability…

Added 0.2% GdCl3 Injected mixing tank Water and filtered Injected mixing tank Water and filtered Removed GdCl3 Test of GdCl3 Addition at 337 nm ~13%/day Preliminary

Added 0.2% GdCl3 Injected Pure 8 MOhm Test of GdCl3 Addition at 400 nm Preliminary Injected Pure MOhm

Added 0.2% GdCl3 Injected Pure 8 MOhm Injected Pure 13 MOhm Test of GdCl3 Addition at 420 nm Preliminary ~8.5% /day

Results Pure water in stainless steel slowly looses transparency at 337, 400 and 420 nm. For 337nm measurements, the water was deoxygenated via nitrogen bubbler to 0.9 ppm (typical air is 8-9 ppm) as measured by dissolved oxygen measurement. For 400nm & 420nm measurements, initial dissolved oxygen was measured at.15 ppm. Addition of GdCl3 makes the water transparency drop much faster (factor of 15). Injection of water from polypro tank shows that water stored there suffered no/little degradation in transparency. Loss of transparency directly from GdCl 3 very small (consistent with 0 at all three wavelengths). 13

GdCl3 effect on transparency

Conclusion: GdCl3 is not a suitable additive for detectors with steel walls. May be OK for other materials.

Current Work: What makes good water go bad? Super-Kamiokande water must be continuously and cleaned – else transparency drops slowly similar behavior seen in IMB (plastic walls) and SNO (acrylic walls – but much slower degradation) REDUCING THE REQUIREMENT FOR RECIRC WILL LOWER COST OF MEGATON SCALE DETETOR

Test with FeCl3 10 ppm Fe+3 ion makes water look like ice tea. Clearly very low levels can affect transparency next week we will test 0.1 ppm slowly raise concentration to measure molar attenuation coefficient test Ni, Cr metal ions for similar behavior

Future Change steel pipe for acrylic one use polypro tank for materials testing of HDPE and other potential plastic liners for LUX and future detectors Investigate coatings for steel for cryostat treatment monitor Water SONGS for stability (acrylic sides)

Backup slides

lower tank (6 sides) - 3/8” thick UVT acrylic, -Gd-water fill -5 side external Tyvek wrap 8 ea. 8” PMTs (1 cm spacing in both directions) Upper tank (5 sides) 3/8” thick UVT acrylic 4 sides external Tyvek wrap Pure water fill to 10 cm Water SONGS 1 cm black Delryn lid 100 cm 50 cm 15 cm 0.2% wt. GdCl 3 50 cm - total external dimensions = 100 cm x 50 cm w x 80 cm ht

The antineutrino interacts with a proton producing… – A 0-7 MeV positron (+ annihilation gammas) – A neutron which thermalizes, captures and creates a delayed 8 MeV gamma cascade – mean time interval ~30 μsec ~ capture time of neutron Both energy depositions and the time interval are measured The time since the most recent muon is also measured Antineutrino Detection 21 _ e + p = n + e +

Background Antineutrinos are not the only particles that produce our coincident signal Cosmic ray muons produce fast neutrons, which scatter off protons and can then be captured on Gd Important to tag muons entering the detector 22