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Radiation at accelerator laboratories

Radiation at accelerator laboratories. Prompt radiation from the particle beam Beam induced radiation Neutrons Gammas Synchrotron radiation Radiation from activated material Activation of air Beam Neutrons. Continued…. Activation of cooling water Radiation protection Shielding …

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Radiation at accelerator laboratories

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  1. Radiation at accelerator laboratories • Prompt radiation from the particle beam • Beam induced radiation • Neutrons • Gammas • Synchrotron radiation • Radiation from activated material • Activation of air • Beam • Neutrons

  2. Continued… • Activation of cooling water • Radiation protection • Shielding • … • Monitoring • Safety precautions • Access restrictions • Interlocks • …

  3. Regulations • Radiation workers (class A) • 20 mSv/a (5-year floating average) • 12.5 mSv/h (1600 h/a) • 50 mSv/a for one year • At JYFL: general limit is 0.5 mSv/h • Rooms with free access

  4. Units • Absorbed dose • D: 1 gray =1 Gy = 1 J/kg • Absorbed dose rate • : Gy/s • Dose equivalent • Quality factor Q • Other biological effects: N (=1) • H: 1 Sievert = 1 Sv

  5. Dose equivalent rate • Effective dose equivalent • wT weight for a specific tissue

  6. Primary beam • Proton beam

  7. Helium

  8. Gamma dose Chinese hamster ovary (CHO) cells

  9. Primary beam • Never apply to living organisms • Except by purpose • Radiation therapy • Sterilization • …

  10. Secondary radiation • Neutrons and gammas from the beam hitting material • Dose rate decreases immediately when the beam is switched off

  11. Residual radiation • Beam hits the accelerator, beam tube or other devices • Protons produce most activities (p,xn) • Co-isotopes from Fe • Secondary neutrons activate material through neutron capture • E.g. 63Cu + n = 64Cu (12.7 h) • Fe isotopes from Fe

  12. “Targets” for thermal neutrons • 63Cu in natural Copper • Sodium in concrete • Argon in air • Zinc in copper • Manganese and cobalt in iron or steel • Antimony in lead • Trace quantities of manganese, cobalt, cesium and europium in earth and concrete • Possibly tungsten-186 in natural tungsten

  13. Other aspects • Minimize the amount of material that can be activated • E.g. inside the accelerator • Ta collimator in the spiral inflector (JYFL) • Proper choice of materials • Depends on accelerated ions and their energies • Cross-sections for nuclear reactions • E.g. 30 Mev (or more) protons induce 22Na from aluminum

  14. Shielding • As close to the source as possible • Distance helps: 1/r2 • Use chicanes (corridors with corners/bends) • Lower pressure in rooms where air may be activated (ventilation) • Use separate water cooling circuit for water that can be activated • Proper choice of materials and the order of materials • Thermalization of fast neutrons first • Material choice depends on neutron energy (10B, Fe, plastics,…)

  15. Shielding… • Assume the “worst” case for dimensioning the wall, floor and ceiling thickness/material • The whole beam is stopped • Which beam? • Light ion • High energy • High intensity • The allowed dose rate (mSv/h) outside the radiating room sets limits for the radiation attenuation

  16. Monitoring • Already according to the Safety License you have to monitor radiation levels (dose rates) • Gamma and neutron monitoring • Alarms • Feed-backs • Interlocks • Personal dose monitoring (class A and B radiation workers) • 4 week intervals (A) • 12 week intervals (B) • For work with a clear risk of dose • Plan the work well • Measure the dose on-line

  17. Permissions • You always need a Safety License by STUK/Radiation and Nuclear Safety Authority for your operation if it may produce radiation!

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