1 / 13

Veto performance for a large xenon detector

Veto performance for a large xenon detector. Sources. Neutrons and gammas from U/Th decay ( α , n), SF. Gammas from Co 60 (1.17 MeV, 1.33 MeV) and K 40 (1.46 MeV). External sources: rock, CR muons … Internal sources: PMTs, copper, steel, target …

aneko
Download Presentation

Veto performance for a large xenon detector

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Veto performance for a large xenon detector IDM 2004, University of Edinburgh

  2. Sources • Neutrons and gammas from U/Th decay (α, n), SF. • Gammas from Co60 (1.17 MeV, 1.33 MeV) and K40 (1.46 MeV). • External sources: rock, CR muons … • Internal sources: PMTs, copper, steel, target … • Neutron spectra from Sources 4A package (LANL). • U and Th gammas from reference spectra (Lewin & Smith, 1990). IDM 2004, University of Edinburgh

  3. Detector configuration • Detector is 250 kg of liquid Xe viewed by array of R8778 PMTs contained in copper vessel. • Surrounded by CH2 veto in stainless steel container 0.5 cm thick. • 10 cm lead shielding outside. • Neutrons and gammas generated in copper vessel and propagated isotropically through the detector. • Internal neutrons only, lead shielding reduces external neutron flux (later). IDM 2004, University of Edinburgh

  4. Contamination levels IDM 2004, University of Edinburgh

  5. Source neutron spectrum IDM 2004, University of Edinburgh

  6. Efficiency for neutrons • Graph shows veto efficiency as a function of veto threshold energy for 5, 10, 20, 30 and 40 g cm-2 (CH2ρ = 1 g cm-3). • Xenon recoils are between 10-50 keV (2-10 keVee). • Proton recoils only. • Quenching factor for protons is 0.2×E1.53 (E in MeV). • Efficiency = • Addition of Gd to CH2 can help improve the efficiency by detecting gamma from neutron capture on Gd. IDM 2004, University of Edinburgh

  7. Xe n Neutron capture • Neutrons can be captured anywhere in the set-up and subsequent gamma may deposit energy in veto. • Efficiency increases from 65% to 82% with increasing Gd loading. • Counting either proton recoils or neutron capture efficiency can increase to 89%. NC & || PR NC only NC only 0.2 % Gd Photon IDM 2004, University of Edinburgh

  8. Reality • Have assumed full 4π veto coverage and infinite time window to detect gammas from neutron capture (not very likely). • Capture time (eτ) inversely proportional to Gd loading: τ = 30μs for 0.1% Gd and 6μs for 0.5% Gd. • For protons τ = 200 μs. • If time window is reduced to 100 μs then efficiency drops to 82%. • For more realistic geometry get 82% efficiency (and 70% with 100μs time window). • One possibility is for a modular veto design. This means less coverage and more gamma/neutron emitting material. Passive CH2with Gd IDM 2004, University of Edinburgh

  9. External gammas • Gammas due to U and Th decay from trace elements in rock, copper PMTs…everything. • Lead shielding can reduce external gamma flux. • Need to have enough shielding in order to reduce background down to levels below that due to internal contamination. IDM 2004, University of Edinburgh

  10. Internal gammas Spectrum of gammas entering target from Cu vessel IDM 2004, University of Edinburgh

  11. Energy deposition in target 2-10 keV 0.9 kg-1 day-1 0.03 kg-1 day-1 0.004 kg-1 day-1 + 40 cm CH2 + 40 cm CH2 0.00002 kg-1 day-1 IDM 2004, University of Edinburgh

  12. Gammas • Veto configuration optimised for neutrons – 40 g cm-2, 0.2 % Gd. • For gammas from copper vessel or PMTs get 40% efficiency between 2-10 keVee, above 100 keV in veto. • Get absorbtion on the Cu vessel walls, veto container and PMTs. • Increasing the energy range causes efficiency to drop. Compton Photoelectric IDM 2004, University of Edinburgh

  13. Conclusions • 70% - 80% veto efficiency for internal neutrons. • 40% efficiency for internal gammas. • Of course, numbers depend upon your detector configuration. IDM 2004, University of Edinburgh

More Related