1. 1 Henderson DUSEL Capstone 05/06/2006 Background Modeling and Clean Room Design Considerations for HUSEP Zeev Shayer and Jonathan Ormes Department of Physics & Astronomy and Denver Research Institute University of Denver zshayer@du.edu

2. Henderson DUSEL Capstone 05/06/20062 The Goal

3. Henderson DUSEL Capstone 05/06/20063 Background What are Sources ? Cosmic Ray and Cosmic Activation Natural Radioactivity from Rock Natural Radioactivity in Materials Radon in Air from U/Th decay series Radioactive Dust ….. How to get rid of it? Underground Laboratory Passive and Active Shielding Material Selection Radon Trapping System (Ventilation) Clean Room

4. Henderson DUSEL Capstone 05/06/20064 Simulation Codes SOURCES-4A/B Code Input: Rock Composition Output: Neutron Production Spectra ( ,n) & S.F. MCNPX Neutron, Gamma and Muon transport (no cascade) + Point Depletion FLUKA Muon Transport and Particle Cascade Calculations GEANT4

5. Henderson DUSEL Capstone 05/06/20065 SOURCES-4A + MCNPX (Neutron and Gamma Background Plus Activation Analysis) Homogenized Rock Composition For Henderson Mine (median, upper bound) ? Neutron Flux 1 – 3 x 10 -6 n/s/cm 2 Average Energy 2.2 – 2.4 MeV ~70% ( ,n) and ~30% (S.F.) Reflection from walls ~20% enhancement

6. Henderson DUSEL Capstone 05/06/20066 Examples of Shielding Design Parrafin Lead

7. Henderson DUSEL Capstone 05/06/20067 Lead Paraffin Lead Lead-Paraffin is preferable (Case A) for exclusively neutron sources, as inelastic scattering in the lead is complemented by elastic scattering in hydrogen of the paraffin. Paraffin-Lead (Case B) is preferable for gamma-ray sources, as energetic gamma-rays scattered in the paraffin (Compton Effect) are rapidly absorbed by lead, which has particularly high absorption cross-section at low energies where the photo-electric effect predominates. Lead-Paraffin is preferable for reduction of the activation products produced in lead through the capture of neutrons Paraffin-Lead is preferable for reduction of secondary gamma-rays due to less gamma-ray produced through the inelastic scattering in lead and paraffin. H Atoms/b/cm ParrafinC 25 H 52 0.0853 PolyethyleneCH 2 0.0789 WaterH2OH2O0.0668

8. Henderson DUSEL Capstone 05/06/20068 Neutron and Secondary Gamma Flux and their attenuations properties Configuration Case Neutron FluxSecondary Gamma Neutron Attenuation Factor Secondary Gamma Production No Shielding22.7281.321E-03-- A4.99E-023.804502880 B1.01E-012.48E-0222519 C6.37E-021.97E-01357149 D5.10E-021.20E-0144591

9. Henderson DUSEL Capstone 05/06/20069 Performance of Various Shielding Block Cases Relative to the “Homogenization” Case (Case D) Reference Case D Neutron Attenuation Relative Factor (Case D/ Case #) Gamma Ray Production Relative Factor (Case #/Case D) D11 A0.99 32 B2.250.21 C1.251.64

10. Henderson DUSEL Capstone 05/06/200610 Gamma K-40 Configuration CaseK-40 Gamma Rays Attenuation Factor A264 B673 C693 D686

11. Henderson DUSEL Capstone 05/06/200611 High Energy Charged Particles - Muon At sea level the muon flux is about ~120 – 140 muons/m 2 /s with mean energy of 4 GeV At 4000 mwe the muon flux is about ~1-3x10 -4 muons/m 2 /s with mean energy of 250 GeV About 10 6 Reduction Factor

12. Henderson DUSEL Capstone 05/06/200612 Neutron Production by Muons from Rock and Shielding Hadronic Cascade Electromagnetic Cascade Spallation Cascade The estimated neutron production from rock (from the literature) ~ 10 -9 – 10 -10 n/s/cm 2 Less than 3 orders of magnitude from U/Th chain production

13. Henderson DUSEL Capstone 05/06/200613 High Energy Charged Particles (100 GeV)– Protons ( Neutron Production within shield material )

14. Henderson DUSEL Capstone 05/06/200614 Neutron energy spectra after 5 cm of the shield block

15. Henderson DUSEL Capstone 05/06/200615 Optimization Methodology for Case D (homogenized case)

16. Henderson DUSEL Capstone 05/06/200616 Optimization Methodology for Case D (homogenized case)

17. Henderson DUSEL Capstone 05/06/200617 Summary Shielding and Clean Room Design Detector components and shielding may become the dominant background Our shielding design approach is different from the ordinary one used in underground laboratories (Lead and CH 2 layers) Easy to optimized for different detector options Less restriction on the contamination of lead with traces of Uranium/Thorium Will need to specify the number of radon atoms per 1 m 3 of air (1000?). (A typical room has around 10 5 particles/m 3 )

18. Henderson DUSEL Capstone 05/06/200618 Summary It is possible to reduce the neutron and gamma from Henderson Mine by Factor of >10 5 To reduce the neutron, gamma and  from detector component 1.Ultra pure material down to ppt 2.Underground storage of important materials 3.Underground assembly Neutrons from Muons 1.Depth underground 2.Active muon veto Radon induced neutron, gamma and  1.System for removing radon 2.Ventilate volumes near detectors with radon free nitrogen