Alternative Detector Designs for Reactor Antineutrinos Jim Lund Sandia National Laboratories

1. Alternative Detector Designs for Reactor AntineutrinosJim LundSandia National Laboratories Applied Antineutrino Physics Workshop • Goals of our collaboration • Designs under consideration • Progress with the segmented scintillator concept • Experiments underway • Work remaining to be done • Summary This work supported by the United States Department of Energy under contract number DE-AC04-94AL85000. Sandia is a multi-program laboratory operated by Sandia Corporation, a Lockheed-Martin Company, for the United States Department of Energy.

2. Goals of our development program • Develop practical anti-neutrino detectors that can be deployed at commercial power reactors • We are beginning to investigate “above ground” detectors The tendon gallery

3. Alternative anti-neutrino detector designs under study by the LLNL-SNL Collaboration • Segmented scintillator • Inverse beta • Water Cerenkov • Inverse beta • Dual Phase Argon • Nuclear scattering • Germanium • Nuclear scattering From Collar group U of Chicago

4. Segmented Scintillator Design • Segmented scintillator • Review of operation • Experimental results • Time multiplexing • Multiplicity cuts

5. ~ 1 m Segmented scintillator design ~10 cm A single voxel Liquid organic scintillator with pulse shape discrimination ZnS(Ag) scintillator with 6Li loading

6. ZnS(Ag) scintillator with 6Li loading n e+ Segmented ScintillatorPrinciples of operation • Neutrino interaction signature • Positron • one cell (discounting annihilation photons) • Electron-like event in liquid scintillator (fast pulse decay) • Neutron • Bright ZnS pulse in two adjacent cells about ~10 ms after positron

7. Existing Detector Mimics antineutrino capture Pulse from n-p scatter Followed by n-capture on Gd Proposed Detector Cut because: n-p scatter distinguishable from pulse shape Rejection of Background events Neutrino-like event Background event (fast neutron capture)

8. Existing Detector Mimics antineutrino capture Pulse from n-p scatter Followed be n-cature on Gd Proposed Detector Cut because: Gamma event very unlikely to be in same cell as neutron event Background eventsslow neutron into detector coincident with gamma ray

9. Existing Detector Mimics antineutrino capture Proposed Detector Cut because: No signal from ZnS scintillator gammas do not deposit enough energy in ZnS and light from neutron on Li is very large = Q= 4.8 MeV Light pulses from more than one cell Background eventstwo chance gamma-rays within time window

10. Segmented Scintillator DetectorDevelopment Progress • Recent experiments • Multiplexing scintillator light • Event identification with segmentation ZnS(Ag) scintillator with 6Li loading n e+

11. ZnS(Ag) scintillator with 6Li loading n e+ Segmented Scintillator DetectorDesign experiments Light multiplexing • To minimize number of PMTs, it would be nice if ZnS signal could be distinguished from liquid scintillator signal by decay time (psd) 2 pmts needed with light multiplexing, 3 (or more) without

12. Light MultiplexingExperimental results Initial experiments by L. Sadler indicate that light multiplexing will probably not work

13. Design solution without light multiplexing Main PMTs Acrylic light guide with LiZnS(Ag) coating ZnS readout PMT ZnS(Ag) scintillator with 6Li loading n e+

14. Segmented Scintillator Detector • Recent experiments • Multiplexing scintillator light • Even identification with segmentation ZnS(Ag) scintillator with 6Li loading n e+

15. One of two plastic detectors installed at San Onofre was modified to perfromsegmentation studies

16. Small “scintillator identification” PMTs were added to one of our plastic detectors installed at SONGs Scintillator identification PMTs Plastic Scintillator Gd containing layer

17. Identification PMT configuration Main PMTs Light guide Holes in light guide for identification PMTs

18. Identification PMT configuration View from below (sans main PMTs)

19. Event multiplicity physics Scintillator identification PMTs • We expect multiple scintillator hits (multiplicity) from energetic neutrons because: • Multi MeV neutrons will have to undergo several large angle elastic scatters to slow and capture on Gd • Inelastic scatters on carbon in the scintillator will produce gamma showers Energetic neutron Plastic Scintillator Gd containing layer

20. Event multiplicity physics II Scintillator identification PMTs • Then again an antineutrino interaction would also have multiplicity • Positron annihilation could also produce high multiplicity Plastic Scintillator Gd containing layer

21. Preliminary multiplicity analysis of SONGS plastic detector data by D. Reyna Evidence for high multiplicity of fast neutrons!

22. Multiplicity analysis of Songs data by D. Reyna Low multiplicity events are random with respect to Gd capture

23. Neutrino-like event Background event (fast neutron capture) Further studies on segmented scintillatorfor 2008 • Light propagation from LiZnS(Ag) • Can we get effective PSD from ~1m length segements? • Monte Carlo studies of neutron slowing down and positron transport

24. Summary and Acknowledgements • We’ve begun design studies of a highly segmented detector with 6LiF:ZnS(Ag) • Some discouragement (probably no multiplexing) but we’re still optimistic • Further experiments in 2008 should complete answers to most important questions • Like to acknowledge everyone in the LLNL-SNL collaboration for helping out with this study: • G. Aigeldinger, J. Brennan, A. Bernstein, N Bowden, S. Dazeley, D. Reyna, and L. Sadler