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Radiation Protection at CERN

Radiation Protection at CERN. C. Theis on behalf of DGS-RP RPE course, 29 th of June 2012. Table of c ontents. Introduction Radiological risks & the radiation environment at CERN Beam on Beam off Radiation monitoring (ARCON-RAMSES) CERN’s radiation protection regulations

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Radiation Protection at CERN

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  1. Radiation Protection at CERN C. Theis on behalf of DGS-RP RPE course, 29th of June 2012

  2. Table of contents • Introduction • Radiologicalrisks & the radiation environmentat CERN • Beam on • Beam off • Radiation monitoring (ARCON-RAMSES) • CERN’s radiation protection regulations • Classification of areas • Classification of radioactive material

  3. CERN’sAccelerators

  4. LHC LHC - injectors LHC - collider 27 km circumference 4 experimental caverns 2 proton beams a 7 TeV CERN accelerator complex 43 km accelerator tunnel = radiation areas 5 experimental areas = radiation areas Auxiliary radiation areas 50 access points

  5. CERN’s Radiation Protection Regulation CERN is an inter-governmental organization and not bound to any national law* - but IAEA Basic Safety Standards Guideline 96/29 Euratom laying down the basic standards for protecting public and workers against the risk of ionisingradiation *) CERN’s relation with its two Host States is defined in conventions between two parties CERN Safety Code F (Radiation Protection Ordinance) and underlying safety instructions, guidelines, etc. Takenfrom B. Lorenz, WKK Symposium April 2008 and modified

  6. CERN’s Radiation Protection • CERN’s radiation protection rules are underrevision released: • Safety Code F 2006 • severalsafety instructions more safety instructions still to beissued to • keep CERN up to the international level • takeintoaccountCERN’sparticularities

  7. General Principles of Radiation Protection • Justification • any exposure of persons to ionizing radiation has to be justified • 2) Limitation • the personal doses have to be kept below the legal limits • 3) Optimization • the personal doses and collective doses have to be kept as low as reasonably achievable (ALARA)* * See specific talks later today

  8. Prompt ionizing radiation Operation of particle accelerators involves beam losses • Prompt ionizing radation (hadrons, leptons, photons)

  9. Radiation showers Radiation showers development after impact of ONEhadron (120 GeV/c ) on a copper target Hadronic shower only Hadronic shower + photons

  10. Particle fields (SPS) Attenuation of radiation H0 (point source): inside the tunnel R: distance to source [m] d: shielding thickness [cm] l: hadron mean free path concrete: l = 40 cm iron: l= 17 cm behind shielding

  11. Ambient Dose Equivalent behind shielding(example: beam loss @ LHCb) Fraction of ambient Particle type Max. energy dose equivalent • Neutrons~1 GeV ~ 80 % • Protons several 100 MeV • Charged pions “ • Muons “ ~ 20 % • Photons “ • Electrons + positrons “

  12. Beam off - induced radioactivity Operation of particle accelerators involves beam losses • Induced radioactivity in equipment components, air, gas, water…

  13. What is activation? Change of nuclear composition of given isotopes resulting in the production of radioactivity At which particle accelerators can activation occur? At all accelerators. However, the radionuclide production rate is much higher at hadron or ion accelerators than those experienced at electron/positron accelerators. • Wheredoesactivationoccurataccelerators? • Atlocationswith (high) particlelosseslike: • Target area • Dumparea • Beam cleaningsectionslikecollimatorsandscraperareas • High-energyphysicsexperiments

  14. Production mechanisms of activation at high-energy accelerators? The primary particle itself or secondary particles interacting with nuclei can produce radioactive isotopes: • Spallation processes • Particle capture (mainly neutrons) • (g,n)-reactions (important for electron accelerators) Courtesy H. Vincke

  15. How do you assess nuclide inventory & activity…. …of a source (e.g. hospital, IRA,…)?  ask the vendor …of accelerator equipment?  calculation/measurement Isotope production Pi: Total track length of particle type k through volume of interest as a function of energy (E) Change of nr. of isotopes Ni(t): Energy (E) and particle type dependent production cross section to produce nuclide i from isotope j Atomic densityof nuclide j in given volume  solve coupled diff. equations (Bateman) with boundary conditions & decay chain treatment  activity

  16. Radiation risk during maintenance Contribution of short-lived radioactive nuclides • Beam line and detector components, tunnel structure, etc. are radioactive • Risk of • external exposure (all work) • internal exposure (destructive work) • Radioactivity of material is function of • chemical composition • impurities • radiation fields • beam energy • beam losses (machine) • luminosity (experiments) Dose equivalent rate (arb. units) Contribution of long-lived radioactive nuclides M. Huhtinen, RPC/2003/XXXVIII/138

  17. Contamination Radioactive contamination at CERN can arise from: • the use of unsealed radioactive sources • activation of air and dust around the accelerators • activation of oils or cooling fluids • the machining or treatment of radioactive components • normal or accidental emissions from targets whilst they are irradiated or after irradiation. Two factors will be considered by the RP Group in defining precautions for the control of unsealed radioactivity: • the prevention of the contamination of personnel and equipment

  18. Personal dosimetry > 6000 persons/year monitored ~ 500 mSv collective dose/year, individual doses << 6 mSv/a Cat. A • radiation workers @ CERN: • Cat. A (<6 mSv/a) and Cat. B (> 6 mSv/a & < 20 mSv/a) • non-radiation workers (< 100 uSv/a) • public (< 10 uSv/a)

  19. Radiation Monitoring - ARCON/RAMSES LHC: RAMSES ARCON: LHC injectors ISOLDE, n-TOF, AD, Experimental areas CNGS: RAMSES CTF3: RAMSES * Injector chain & experimental areas will be upgraded to RAMSES

  20. Stray radiation Monitoring Ventilation Monitoring Water Monitoring station Wind Monitoring VGM - VAS RWM - RWS ERC EPIC USA Monitors for Protection of Environment ARCON and RAMSES use the same/similar type of monitors

  21. Air filled ionisation chamber REM counter Gas filled, high pressure ionization chamber Operational Radiation Protection Monitors ARCON and RAMSES use the same/similar type of monitors Beam-off: to protect workers during maintenance and repair against radiation fields caused by decay of radionuclides (mainly gammas, E < 2.7 MeV) No alarm function Beam-on: to protect workers in areas adjacent to accelerator tunnels and experiments against prompt radiation(mainly neutrons, E < some GeV) Alarm function

  22. Radiation Alarm Unit(RAMSES) Operational Radiation Protection Monitors Special monitors Monitoringstation Site Gate Monitor Hand & Foot monitor RAMSES: reading of radiation levels directly available ≠ ARCON

  23. Can I use any detector in any field? 241AmBe calibration source LHCb behind shielding wall • Rad. detectors @ high energy accelerators needs to be carefully characterized • Choose detector carefully based on which field you need to measure in • Calibrate your detector according to the field (e.g. MC based field calibration)(e.g. a standard REM counter would underestimate by ~2 behind the LHCb shielding wall)

  24. CERN’s area classification permanent low occupancy Courtesy N. Conan, M. Widorski Safety Instruction S3-GSI1, EDMS 810149

  25. Operation 2012 Close to the beam-pipeof the ATLAS, CMS detectors PS-, SPS- and LHC- experimental areas PS, SPS, PS & SPS target areas, ISOLDE, n-TOF, CNGS, HiRadMat simple controlled non-designated prohibited limited stay high radiation supervised 2.5 uSv/h 15 uSv/h 50 uSv/h 2 mSv/h 100 mSv/h Pt 3, 6, 7 arcs LHCacc.

  26. Area classification with respect to internal and external contamination No contamination: < 1 Bq/cm2 for non-identified gamma and beta emitters < 0.1 Bq/cm2 for non-identified alpha emitters

  27. Area classification with respect to internal and external contamination No contamination: < 1 Bq/cm2for non-identified gamma and beta emitters < 0.1 Bq/cm2 for non-identified alpha emitters

  28. Alarm levels for designated areas Radiation measurement: typical sampling time: 100 -300 s  extrapolation to 3600 s  above limit: alarm Beam-On: accessible areas are shielded towards beam areas -> classification as Supervised Radiation Area or Simple Controlled Radiation Area is sufficient not applicable not applicable Monitors in designated areas (accessible during beam on): uniform alarm and interlock levels not applicable

  29. When is a material radioactive? • Activity • Specific activityexceeds the CERN exemption limits as given in Table 2 (column 2) of EDMS doc 942170 AND • total activityexceeds the CERN exemption limits as given in Table 2 (column 2) of EDMS doc 942170. OR • Dose rate • Ambient dose equivalent rate measured in 10 cm distance of the item exceeds 0.1 uSv/h after subtraction of the background. • Slightly radioactive < 10 uSv/h • Radioactive < 100 uSv/h • Highly radioactive > 100 uSv/h OR • Surface contamination • 1 Bq/cm2 in case of unidentified beta- and gamma emitters and 0.1 Bq/cm2 in case of unidentified alpha emitters. Once a radio-nuclide has been identified then the CS-values given in Table 4 of EDMS doc 942170 can be used.

  30. When is a material radioactive? Design studies ... the minimum of the exemption limits proposed in Refs. [5,7,8] which will be adopted by future European Directives and national legislations.

  31. Release of material LHC tunnel (LSS, DS, Arcs, etc.), all injectors, etc. Individual radiological control: • activation of material cannot be excluded by reasoning • individual control by RP of each material leaving the area required • material classified as “radioactive”: • handling is subject to Safety Code F • needs to be traced

  32. Release of material Service areas and technical galleries of LHC (US, UA, UJ) : Globalradiological control • level of stray radiation sufficiently low to exclude activation of material • radiological “control” by “reasoning”: • ambient dose equivalent rate measurements • global activity measurements (e.g. in-situ g-spectroscopy) • analysis of representative material samples and TLD detectors • use and/or storage of radioactive material are not permitted Cu Pb Ag Steel Al TLD

  33. DGS-RP-AS contact info

  34. Further info… Other RP services (shipping, sources, analytic lab, rad. waste,…) https://espace.cern.ch/hse-unit/en/structure/Pages/RP.aspx Further useful information & links (procedures, area classification,…) https://www.cern.ch/rp-lhc Dose & work planning (DIMR): https://espace.cern.ch/rpps/wdp

  35. The presentation is based on the work of the staff, fellows and students in the Radiation Protection Group at CERN. In particular : • I. Brunner, M. Brugger (EN-STI), N. Conan, D. Forkel-Wirth, • A. Herve, A. Hess, S. Roesler, C. Tromel, H. and Hz. Vincke

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