1. LCLS Radiological Considerations Sayed H. Rokni, SLAC April 24, 2002
Radiological safety program at SLAC (S. H. Rokni)
Shielding methodology for LCLS (W. R. Nelson)
Radiation safety systems for the LCLS (S. Mao)
LCLS DOE Review, April 24, 2002
Sayed Rokni, SLAC

2. Outline of the Presentation
Radiological safety program at SLAC
ALARA/dose limitation
Design criteria
Radiation safety systems
Passive/active components (BCS)
Access control systems (PPS, HPS)
Administrative
Overview of the systems specific to LCLS
Existing facility (FFTB)
New components
LCLS DOE Review, April 24, 2002
Sayed Rokni, SLAC

3. Radiation Safety at SLAC
Ensure ALARA
Provide adequate shield for facilities, beam lines and experimental areas
Control access to areas where beam could be present
Incorporate dose reduction, contamination reduction, and waste minimization features in planning stage
Prevent any person from receiving more radiation exposure than limits
LCLS DOE Review, April 24, 2002
Sayed Rokni, SLAC

4. Radiological Safety at SLAC-Cont.
Engineering and administrative systems to implement the program
SLAC Radiological Control Manual
Radiation Safety Systems, Technical Basis Document
Guidelines for Operation
Implemented by Radiation Physics, Operational Health Physics, Accelerator and SSRL Safety Offices, Controls Departments
LCLS DOE Review, April 24, 2002
Sayed Rokni, SLAC

5. Engineering Controls for Radiation Safety
Passive
Bulk Shielding, local shielding: attenuate radiation
Protection collimators: limiting apertures prevent beams from striking shielding
Active Sensors
Beam Containment System (BCS): Sensors that turn beams off when parameters exceed pre-set limits
Ion chambers
Torroids
LCLS DOE Review, April 24, 2002
Sayed Rokni, SLAC

6. Engineering Controls-Cont.
Access Control System
Prevents access to areas where potential for beam operations exist
Personnel Protection System (PPS)
Hutch Protection System (HPS)
LCLS DOE Review, April 24, 2002
Sayed Rokni, SLAC

7. Design of Engineering Controls
Radiation Physics Department staff have been involved in design of shielding, BCS and PPS specifications for the LCLS from the start: Design Study Report, Environmental Assessment, Conceptual Design Report
Staffing:
K. R. Kase W. R. Nelson
H. Khater A. Prinz
J. C. Liu S. H. Rokni
S. Mao H. Vincke
LCLS DOE Review, April 24, 2002
Sayed Rokni, SLAC

8. Radiological Safety at SLAC- Operations
Radiation physics has oversight for beam operations in conjunction with: Accelerator and SSRL Safety Offices
Administrative controls:
Conduct of Operations, Configuration Control
Guidelines for operations
Beam Authorization Sheets (BAS)
Radiation Safety Work Control Forms (RSWC)
Accelerator and SSRL safety procedures
LCLS DOE Review, April 24, 2002
Sayed Rokni, SLAC

9. Radiological Safety at SLAC-Cont
OHP administers the following services:
Training
Instrumentation
Radiological Postings
Dosimetry
Radiological Surveys & Monitoring
Radiological Hygiene
Radioactive Material Inventory Control
Radioactive Waste Management
Radiological Environmental Protection
Emergency Preparedness
LCLS DOE Review, April 24, 2002
Sayed Rokni, SLAC

10. ES&H Division and Radiation Safety Management
LCLS DOE Review, April 24, 2002
Sayed Rokni, SLAC

11. Shielding Design Criteria
Normal mode of operation
The integrated dose equivalent outside the the FFTB tunnel must not exceed 1 rem/yr
The integrated dose equivalent to personnel working inside and around the experimental hutch shielding barriers must not exceed 0.1 rem
Maximum Credible Incident
The dose equivalent-rate is limited to less than 25 rem/h, and integrated dose equivalent of less than 3 rem
LCLS DOE Review, April 24, 2002
Sayed Rokni, SLAC

12. Final Focus Test Beam Designed for: 2.5 kW 50 GeV e- or e+ beams
FFTB Tunnel
4’ thick concrete side walls
3’ thick concrete roof
FFTB Dump
9’ thick iron, concrete walls
60’ of iron to shield muons
LCLS DOE Review, April 24, 2002
Sayed Rokni, SLAC

13. LCLS Radiation Safety Systems
Additional components for the LCLS
Injector shielding at sector 20
lateral shielding walls of the optical front end
front, back and lateral shielding walls for the electron dump
experimental hutches shielding
Front End and hutch beam stoppers
entrance maze
HPS
Initial design completed
Optimize the design
LCLS DOE Review, April 24, 2002
Sayed Rokni, SLAC

14. LCLS DOE Review, April 24, 2002
Sayed Rokni, SLAC

15. LCLS Radiological Considerations Walter R. Nelson, SLAC April 24, 2002
Radiological Safety Program at SLAC (S. H. Rokni)
Shielding Methodology for LCLS (W. R. Nelson)
Radiation Safety Systems for the LCLS (S. Mao)
LCLS DOE Review, April 24, 2002
Sayed Rokni, SLAC

16. Shielding Methodology – Outline of Talk
Radiation fields around an electron accelerator
Electromagnetic cascades (soft showers)
Photoproduction of neutrons and muons
LCLS geometry “sources of radiation”
Shielding methodology (computer codes)
Example results using the EGS4, MUON89 and MuCarlo codes will be presented
Relevant shielding results will be presented in the talk that follows (by Stan Mao)
LCLS DOE Review, April 24, 2002
Sayed Rokni, SLAC

17. Electron-photon interactions and EM showers
Understanding the electromagnetic cascade shower is key to understanding radiation fields at electron accelerators
High-energy electrons and positrons produce lots of x-rays
X-rays in turn produce more electrons and positrons (in pairs)
This continues back in forth – but it eventually stops when all of the energy is used up
Process is called an electromagnetic cascade “shower”
First observed in photographs like the one shown in the…
… next slide
LCLS DOE Review, April 24, 2002
Sayed Rokni, SLAC

18. Cloud chamber photo of a shower (circa 1950)
(Note: only charged particles are visible)
High-energy electron enters from top
Strikes Pb sheet (not visible in photo)
Many more charged particles produced
They bend because of magnetic field
Charged particles are both e+e- (pairs)
e+e- get swept out by the magnetic field
Take note of the two other Pb sheets
Shower regenerated by invisible photons
Without the magnetic field, the shower
would be very forward-directed
LCLS DOE Review, April 24, 2002
Sayed Rokni, SLAC

19. Monte Carlo simulation showing initiation of a shower
100 MeV electron impinges from the left onto a 1-cm slab of Pb.
Particles are produced and are identified by their color.
LCLS DOE Review, April 24, 2002
Sayed Rokni, SLAC

20. Ten 1-GeV electrons strike a 15-cm Cu target
All particles are shown Only electrons and positrons shown
LCLS DOE Review, April 24, 2002
Sayed Rokni, SLAC

21. …Real example of the power of a full EM shower
Melt-down at shower maximum e-
A Cu beam stopper (PPS/BCS device) that was destroyed by the beam
LCLS DOE Review, April 24, 2002
Sayed Rokni, SLAC

22. …Real example of the power of a full EM shower (cont.)
Note: THREE shower maxima
A Cu beam stopper (PPS/BCS device) that was destroyed by the beam
LCLS DOE Review, April 24, 2002
Sayed Rokni, SLAC

23. Photoproduction of other particles (radiation)
Although most of the energy in an EM shower goes into ordinary “energy deposition” (i.e., heat), other particles are produced
About 0.2% goes into hadron production --- i.e., neutrons
Half into low-energy neutrons (giant resonance excitation)
Half into high-energy neutrons (hadronic cascade)
And muons are pair produced at a rate that is about 1/40,000th that of electron-positron pairs
Although these numbers may seem small, these other radiations are more difficult to attenuate than photons
LCLS DOE Review, April 24, 2002
Sayed Rokni, SLAC

24. General schematic of radiation and shielding
Electron beam enters from the left and produces a shower
Photons from shower itself must be shielded
Neutrons produced by photons must be shielded
Muons produced by photons must be shielded (forward direction)
LCLS DOE Review, April 24, 2002
Sayed Rokni, SLAC

25. A closer look at how radiation gets shielded
Low-energy neutrons attenuate rather easily
They are followed by the photons
When the shield gets “thicker” the high-energy neutron component starts to dominate
Ultimately we may be stuck with muons, which attenuate very slowly
This is what happens at 0°
At 90° things look similar…except we don’t have muons
For the LCLS we have to consider both the forward and side directions
LCLS DOE Review, April 24, 2002
Sayed Rokni, SLAC

26. Components along the LCLS (Sources of Radiation)
An Injector (at Sector 20) feeds into the main SLAC Linac
15 GeV electron beam with 2 kW of power at the east end
7 x 109 electrons/pulse at 120 Hz (130 nA of beam current)
The electrons pass through an Undulator that generates a coherent beam of x-rays
A beam line allows x-rays to go to experimental Hutches
Another beam line sends the 15 GeV electrons to a Dump
Collimators and stoppers are required for PPS purposes
All must be considered in the radiation safety analysis
LCLS DOE Review, April 24, 2002
Sayed Rokni, SLAC

27. Sources of radiation (cont.)
Undulator
Collimators
Stoppers
Beam dump
Electrons will hit all of these components…
… and so will the photons
The result:
radiation !!!
LCLS DOE Review, April 24, 2002
Sayed Rokni, SLAC

28. Sources of radiation (cont.)
We have sources resulting from the 15 GeV electron beam
Beam halo
Gas bremsstrahlung
Mis-steering
Beam-diagnostic devices
The electron dump
We also have x-ray sources created by the undulator
Coherent (FEL) radiation
Synchrotron radiation
LCLS DOE Review, April 24, 2002
Sayed Rokni, SLAC

29. Shielding Methods
The Radiation Physics Department has successfully shielded the SLAC Two-Mile Accelerator, and its beam lines, for about 40 years
A good starting reference is:
Chapter 26: “Shielding and Radiation” in The Stanford Two Mile Accelerator,
R. B. Neal, Editor (W. A. Benjamin, Inc., New York, 1968).
Many problems can be solved by using existing computer codes, which we categorize into three groups
Monte Carlo: EGS4, FLUKA, and MuCarlo
Analytic: MUON89, STAC8 and PHOTON
Semi-empirical (scaling): SHIELD11
The four codes highlighted above in “blue” were developed within the RP department
LCLS DOE Review, April 24, 2002
Sayed Rokni, SLAC

30. Monte Carlo codes: EGS4, FLUKA, and MuCarlo
EGS4 is a program that specializes in the production and transport of electrons, positrons and photons through matter. It is the most thoroughly benchmarked shower code and is generally considered the standard by which other EM codes are judged.
FLUKA is a general program for producing and transporting more than 30 different particles, including neutrons, muons, and for solving the EM shower problem.
MuCarlo takes muons that are produced by electron beams striking beam dumps and transports them through very complex geometries (including magnet fields).
LCLS DOE Review, April 24, 2002
Sayed Rokni, SLAC

31. Analytic codes: MUON89, STAC8 and PHOTON
MUON89 determines the fluence of muons through thick shields after they have been produced in an EM shower initiated by a beam of electrons striking a dump.
PHOTON is an x-ray shielding code that was specifically designed to determine radiation levels associated with beam lines at synchrotron light facilities.
STAC8 was developed from PHOTON and contains many improvements, such as undulator radiation, build-up factors, angular-dependent coherent and incoherent scattering, self-shielding by scatterers (including inclined scatterers), etc.
LCLS DOE Review, April 24, 2002
Sayed Rokni, SLAC

32. Semi-empirical codes: SHIELD11
SHIELD11 is the “workhorse” code of the department and is based on the scaling of experimental data taken during the early days of SLAC. The components and methods of the code have been used with great success in shielding design not only at SLAC, but also at KEK and Jefferson Lab.
LCLS DOE Review, April 24, 2002
Sayed Rokni, SLAC

33. An example calculation using EGS4
EGS4 was used to determine where the electron beam produces showers and how much energy gets deposited in stoppers
LCLS DOE Review, April 24, 2002
Sayed Rokni, SLAC

34. An example calculation (cont.)
Energy absorbed all along the undulator
Specific peaks at:
Collimator C1a
Collimator C2
Collimator C3
Stopper ST3
Energy fraction absorbed in ST3 is about 6x10-4, which corresponds to 12 mW (for a 2 kW electron beam)
LCLS DOE Review, April 24, 2002
Sayed Rokni, SLAC

35. Another example calculation using MUON89
We used MUON89 for the forward dump shielding analysis
Note the isodose (rate) lines below the ground level
LCLS DOE Review, April 24, 2002
Sayed Rokni, SLAC

36. Summary
The shielding of muons from the primary electron beam striking the dump is well understood
The energy deposition along the LCLS itself – from the Undulator down through the Hutches – has been quantified
Using this information, an extensive shielding analysis has been done by the Radiation Physics Department and the results will be discussed in the next talk (by Stan Mao)
LCLS DOE Review, April 24, 2002
Sayed Rokni, SLAC

37. LCLS Radiological Considerations Stan Mao, SLAC April 24, 2002
Radiological Safety Program at SLAC (S. H. Rokni)
Shielding Methodology for LCLS (W. R. Nelson)
Radiation Safety Systems for the LCLS (S. Mao)
LCLS DOE Review, April 24, 2002
Sayed Rokni, SLAC

38. Radiation Safety Systems for the LCLS
Injector at LINAC Sector 20
Electron dump line
Beam containment system
Shielding
Front End Enclosure
Experimental Hutch
Front End Enclosure stoppers and Hutch stoppers
LCLS DOE Review, April 24, 2002
Sayed Rokni, SLAC

39. Injector at LINAC Sector 20
LCLS DOE Review, April 24, 2002
Sayed Rokni, SLAC

40. Injector at LINAC Sector 20
LCLS DOE Review, April 24, 2002
Sayed Rokni, SLAC

41. Electron dump line
LCLS DOE Review, April 24, 2002
Sayed Rokni, SLAC

42. Beam containment system (BCS)
LCLS DOE Review, April 24, 2002
Sayed Rokni, SLAC

43. Dump shielding 1
LCLS DOE Review, April 24, 2002
Sayed Rokni, SLAC

44. Dump shielding 2
LCLS DOE Review, April 24, 2002
Sayed Rokni, SLAC

45. Front End Enclosure
LCLS DOE Review, April 24, 2002
Sayed Rokni, SLAC

46. Front End Enclosure - continued
LCLS DOE Review, April 24, 2002
Sayed Rokni, SLAC

47. Experimental Hatch
LCLS DOE Review, April 24, 2002
Sayed Rokni, SLAC

48. Front End Enclosure stoppers and Hutch stoppers
LCLS DOE Review, April 24, 2002
Sayed Rokni, SLAC

49. LCLS Radiological Considerations- Summary
Radiation safety issues for the LCLS are similar to issues normally encountered at high energy electron linacs and synchrotron radiation facilities.
Staff from Radiation Physics Department are involved in the design of shielding and specifications for active radiation safety systems for the LCLS.
SLAC has a well established radiological safety program to oversee the safe operation of the LCLS.
LCLS DOE Review, April 24, 2002
Sayed Rokni, SLAC