Radiation Protection and Radiation Safety for Particle Accelerator Facilities J. Vollaire, Radiation Protection Group CERN Compact Accelerators for Isotope Production (March Cockcroft Institute)

Table of Content General Principles of Radiation Protection Radiological risks and Accelerator design Some example of design studies Monitoring Conclusions Visite Conjointe 27/02/2015Compact Accelerators for Isotope Production 2

General Principle of Radiation Protection Objective: Provide a level of protection of humans and their environment from the harmful effect of ionizing radiations without unduly limiting the beneficial practices giving rise radiation exposure Three principles: Justification, Optimization and Dose Limitation In practice: Definition and implementation of measures as training, shielding, radiation monitoring, work-procedures, access control, radiological classification, interlocks, dosimetry, material control and tracking… Compact Accelerators for Isotope Production 3

Radiation Protection quantities Absorbed Dose: deposited energy per unit of mass Dose Equivalent: deposited energy weighted by a radiation dependent factor (Sievert) Effective Dose: Sum of dose equivalent weighted by tissue or organ dependent factors (Sievert) Operational parameters: Human is represented by a sphere (1 g/cm3) and the dose equivalent is determined for two depths (0.07 mm and 10 mm) In practice external irradiation is determined from the operational parameters Compact Accelerators for Isotope Production 4

Legislation and limits Tripartite 2nd October Compact Accelerators for Isotope Production 5 Dose Limit “De minimis” dose Occupational exposure (stochastic effects) Negligible Acceptable Tolerable Not-Acceptable Optimization System of Radiation Protection used in Europe and worldwide is based on the recommendation of the International Commission on Radiation Protection Optimization leads to the introduction of dose constraints (tool for planning process) Dose Limitation : limit to individual for planned exposure Different limits for workers, patients and member of the public

Legal limits over time…. Tripartite 2nd October Source: Los Alamos Science Nr. 23, 1995, p. 116 M. Curie ICRP 103 Compact Accelerators for Isotope Production 6 EDMS No.

Operational Limits (Example CERN) 2000 working hours / year (Example: Supervised Radiation Area = 6 mSv/y ) Low occupancy < 20 % of working time Dosimetry requirements, training, work planning and authorization…. Compact Accelerators for Isotope Production 7

Radiological risks with hadron accelerators Beam “on”: inelastic interaction of protons from the beam (target, loss aperture, reduction…) – Intra-nuclear cascade with neutron emission – Emission of fast neutrons evaporation), thermalisation and capture Beam “off”: Target nuclei in an excited state (neutron deficient  + emitter) Residual radiations 8 Compact Accelerators for Isotope Production 8

Mitigation of prompt dose risks Personnel Protection System: – Access Control System: Prevent personnel access to areas with high radiation levels (patrol, token, operator supervision…) – Terminate the operation in case of abnormal situation Shielding (passive protection): – attenuates stray radiation to acceptable levels in areas accessible to personnel Active Protection: Alarms, radiation monitors, beam loss monitor, current monitor, other interlocks… Compact Accelerators for Isotope Production 9

Activation and Residual dose rate Reduction of personnel exposure relies on the optimization in the design phase and operation Design: Material choice, reduction of beam losses, facilitation of interventions Management of cooling fluids and air (protection of accessible areas, use of static and dynamic confinement for the air) Operation: Cooling time, operational dosimetry and dose planning, optimization of interventions (shielding, training, remote handling….) Dismantling, waste production and elimination Compact Accelerators for Isotope Production 10

(Some) Guidelines for facilities design Define the beam parameters (envelope for the intensity and energy) and operating conditions (duty factor, maintenance periods and duration) Perform conservative estimate of the beam losses – “Normal losses ” inherent to the operation – Risks of full beam loss (mis-steering) Define the envelope of the accessible areas during operation (access system) Design the shielding and active system Compact Accelerators for Isotope Production 11

Shielding Design First estimate of the bulk shielding using analytical formula to define – The “source term” based on the beam properties – Attenuation and dose reduction with distance Monte-Carlo code are necessary to assess special cases (access maze, penetrations…) and optimize the material choice (based on the radiation field) Different codes are available (MCNPX, FLUKA, PHITS, MARS, PENELOPE, GEANT4, EGS4…) Compact Accelerators for Isotope Production 12

Radiation Protection studies at CERN Tracks from a single 450 GeV protons Compact Accelerators for Isotope Production 13

Example: wave guides Linac4 14 New H - accelerator for all the proton physics at CERN Beam line is underground (no access) and the klystron hall at the surface is accessible during operation Compact Accelerators for Isotope Production 14

Normal beam losses Early design based on 1 W/m beam loss (hands on maintenance) Worst case for a point loss considered is 10 W Detailed FLUKA geometry of the duct geometry Use of region importance biasing in order to have equivalent statistics between direct penetrations and streaming contributions Compact Accelerators for Isotope Production 15

Full Beam loss Compact Accelerators for Isotope Production 16 Commissioning beam dump (temporary system to stop the beam at 100 MeV) Dump core: Graphite plate with water cooled copper Iron and steel shielding

Linac4 Beam Dump (activation) Tripartite 2nd October Compact Accelerators for Isotope Production 17 Shielding Fe + Colemanite concrete blocks Optimization of intervention in case of dump core failure

Example: Calibration Hall (CERN) New calibration hall and irradiation facility with  and neutron sources (Am-Be) Routine calibration of monitors and dosimeters (high occupancy of neighboring rooms) Compact Accelerators for Isotope Production 18

Results for the Am-Be source Possibility to define a user source routine to sample primary neutrons Detailed geometry with 3D visualization possible For example, possibility to assess possible skyshine effect and impact of the penetration in the ceiling Compact Accelerators for Isotope Production 19 Fabio Pozzi Thesis in preparation

Similar calculations for the  irradiator Compact Accelerators for Isotope Production 20 Radioactive isotope can be used as a source in FLUKA (built-in) Example: Results for the Cs-137 source case Fabio Pozzi Thesis in preparation

MEDAUSTRON Facility Ion therapy facility (proton and carbon) built in Austria Radiation Protection study and shielding design done in collaboration with CERN Use of sandwich shielding to limit the construction cost 21 Compact Accelerators for Isotope Production 21

MEDAUSTRON shielding analysis Jaegerhofer, Lukas. Shielding and Radiation studies for MedAustron. Thesis, CERN 2011 Compact Accelerators for Isotope Production 22 Detailed studies to assess the effect of the sandwich shielding approach

SPES Project (INFN Legnaro) Compact Accelerators for Isotope Production 23 BEST Cyclotron installation 70 MeV proton beam 750  A Radio-Isotopes for Medicine Production & re-acceleration RIBs from p-induced Fission on UCx Accelerator based neutron source (Proton and Neutron Facility for Applied Physics)

Activation Calculations for SPES Current loss: 5% of 250 uA Energy of the proton beam: 40 MeV Extraction periods: runs, 14 days/run Differtent irradiation patterns (number of runs) and cooling time Useful to assess collective dose for the facility maintenance Example 1 run and 1 hour cool down Compact Accelerators for Isotope Production 24 Lucia Sarchiapone INFN Legnaro

HFM Radiation Monitoring 25 High pressure ionization chamber air filled ionization chamber Gate Monitor Compact Accelerators for Isotope Production 25 +

Conclusions Compact Accelerators for Isotope Production 26 Radiation Protection aspects must be considered early in the design phase Shielding options depend on constraints (space, budget, activation, prompt radiations, availability…) MC code allows to simulate complex geometries and make systematic studies of materials Many aspects not mentioned here (contamination, environmental impact, waste….)

Acknowledgement A lot of material shown taken from my colleagues in the Radiation Protection Group at CERN Compact Accelerators for Isotope Production 27