A Water-Based Neutron and Anti-Neutrino Detector

1. A Water-Based Neutron and Anti-Neutrino Detector R.Svoboda

2. Neutron Detection – Fast Neutrons “Fast” neutrons are those with kinetic energy above a few 10’s of keV - energetic nuclear decays - fission - fusion - high energy interactions on nuclei nucleus m fast neutron N R.Svoboda

3. Fast Neutron Detection N recoil proton P g capture gamma N thermalization nucleus R.Svoboda

4. Anti-Neutrinos • NuclearReactors • Supernovae • Beta decay of neutron-rich nuclei • accelerator beams R.Svoboda

5. Anti-Neutrino Detection g _ 511 keV Eion n e+ e+ e- Prompt p p g n 511 keV g n 2.2 MeV p ~200 ms Delayed R.Svoboda

6. Liquid Scintillator • Organic liquid scintillator sensitive to both recoil protons, capture gammas, and positron annihilation – that’s good. Used since 1950’s. • These liquids which are often toxic and many common ones are flammable - that’s bad. Example is pseudocumine. • Disposal and environmental concerns always a problem, even for less flammable and toxic compounds R.Svoboda

7. Liquid Scintillator • Expensive for detectors in the kton or larger range. • Most scintillators have capture time of ~200 ms – this is often too long due to backgrounds • 2.2 MeV gamma is near 208-Tl 2.6 MeV gamma – from natural thorium chain • solution – dope with high-cross section, high capture energy additive. Gadolinium is most popular due to extremely high cross-section for capture and 8 MeV gamma cascade. • metal doping makes most scintillators chemically unstable and/or very sensitive to environmental conditions. R.Svoboda

8. charged particles moving faster than speed c/1.33 give off broadband “Cherenkov” radiation water is cheap, non-toxic, non-flammable (except in Cleveland) 2.2 MeV capture gammas Compton scatter off atomic electrons – too low energy to see! Water Cherenkov Detectors Super-Kamiokande R.Svoboda

9. tracking detectors not sensitive to fast neutrons below few GeV good for thermalizing fast neutrons – just can’t see them when they capture Why Not Dope With Gd Also? Water Cherenkov Why would we like to see neutrons? R.Svoboda

10. Galactic Supernovae SN1987A • Massive stars end their life by collapse into a neutron star or black hole. In this process they give off 99% of the collapse energy (which is huge) in neutrinos of all types. • The spectrum and time evolution of the neutrinos is of great scientific interest as it is the only way to directly observe this process • Cross-section for antielectron-neutrinos is much higher than others by factor of 20-30. Only they give off neutrons. If these can be removed we can pull out the specta of the other types, which come from deeper inside the baby neutron star. • Understanding these violent explosions gives a direct handle on how heavy elements are synthesized. R.Svoboda

11. It is expected that there is a cosmological background of relic SN neutrinos Sensitive to history of star formation in universe Major background limiting SK do not have coincident neutrons Relic Supernovae Super-K Theories of stellar formation R.Svoboda

12. Reactor Safeguards • LLNL and SNL have a joint project to develop antineutrino detectors for use in measuring plutonium content in running reactors in situ • A prototype detector is now running at San Onofre Nuclear Generating Station (SONGS) • These detectors must be located right outside the reactor containment vessel • Concern with safety • Concern with stability of detector sensitivity over many years. Also very temperature sensitive. R.Svoboda

13. Other Possibilities • Potential for very large neutron-sensitive neutrino detectors • could detect reactors from long distances • KamLAND can just see Kashiwazaki power plant 180 km away with 0.5 ktons. We could go much larger. R.Svoboda

14. Who Are We? • R.Svoboda: many years experience in neutrino detection (SN1987A, Solar Neutrinos, Reactor Neutrinos). Former Navy Nuclear Power Officer. • Hank Sobel: professor at UCI with similar experience • Mark Vagins: Researcher at UCI, published original concept • Steven Dazeley: visiting postdoc from LSU • William Coleman: grad. student visitor that this proposal would help support for a summer visit. R.Svoboda

15. What Do We Want to Do? • We have done some preliminary work on evaluating this concept via an Office of Science ADR Grant. Final report submitted last month. • No “Show Stoppers”, but some problems uncovered • There are still potential “Show Stoppers” we would like to test for by making a small test detector here at LLNL R.Svoboda

16. ADR Study • Will adding GdCl3 to water cause corrosion problems for detector components? • Will Gd-loaded water still be transparent at the 100-m scale? • How can Gd-loaded water be cleaned? Empirically, this continuous cleaning is required in large detectors, but the reasons are not understood R.Svoboda

17. 1 year soak test in high GdCl3 concentration (~30 years) 50 materials, most are OK some problems Initial Corrosion Test Tank Steel Weld points R.Svoboda

18. What is Happening? • Water has dissolved oxygen – this is likely the culprit • need to do test in sealed, de-oxygenated water tank • also need to test full Photomultiplier Assembly (basic component of all Water Cherenov Detectors) due to worries about galvanic corrosion R.Svoboda

19. Cleaning Concepts • Working with a local California small business (South Coast Water) UCI has worked out on test bench a concept for cleaning water with GdCl3 • Not possible to determine effectiveness with typical small (10 cm) photospectrometer – need larger test bed • Also – can we determine why we have to clean the water at all? R.Svoboda

20. Test Tank at LLNL photodetector 3.5 m UV laser Cleaning system Test bed R.Svoboda

21. Goals • Measure water transparency over 3.5m (maybe 7m) baseline as a function of GdCl3 concentration up to 1.0% • Test for corrosion after 6 mos exposure in de-oxygenated water at 1% (~5 years) • See if water cleaning effective, try out new ideas R.Svoboda

22. Instrument for measuring the transparency of GdCl3 doped water at LLNL R.Svoboda

23. Tuneable dye laser will be injected and reflected back. Gd concentration is Variable. A “micro-SuperK” is also being built to test anti-corrosion schemes. R.Svoboda