Performance Requirements for Monitoring Pulsed, Mixed Radiation Fields Around High-Energy Accelerators

Transcription

1 Performance Requirements for Monitoring Pulsed, Mixed Radiation Fields Around High-Energy Accelerators D. Forkel-Wirth Wirth, S. Mayer, H.G. Menzel, A. Muller, T. Otto, M. Pangallo, D. Perrin, M. Rettig, S. Roesler, L. Scibile*, H. Vincke, CERN SC-RP, CERN TS-CSE* C. Theis TU Graz, Graz, Austria M. Latu Saphymo-Genitron Genitron-Novelec, Grenoble, France 1

2 Contents Metrology in High-Energy Mixed Radiation Fields Metrology Comparison between experiment and Monte Carlo simulation for High-pressure ionisation chambers (H, Ar filled) Air filled plastic ionisation chambers Recombination effects Technique Read-out electronics: charge digitizer Conclusion 2

3 Radiation Protection Task Radiological survey of work places: Measurement of ambient dose equivalent H*(10) [Sv] in pulsed, high energy, mixed radiation fields Challenge: Correct Reliable State-of of-the-art Compliant with international standards and legal requirements Radiation Monitoring System for the Environment and Safety for LHC (RAMSES) 3

4 Monitoring of Ionising Radiation Radiation Monitor with ID + local database Monitor Controller Basic Area Controller Tap box with location ID Direct hardware connection Radiation Display Display Control box Monitoring of dose rates caused by by Prompt radiation (beam on) Induced radioactivity (beam off) off) 4

5 Mixed High-Energy Radiation Fields neutrons < few GeV photons protons neutrons < 15 MeV photons muons pions kaons positrons proportional to absorbed dose (Gy) in detector Signal (charge) ambient dose equivalent H*(10) in Sv electrons detector calibration factor field calibration factor Detector response to mixed fields? 5 => Experiment Monte Carlo simulation

6 Comparison of Experiment and Simulations PMI wall: C-H2 volume: 3 l gas: air, 1 atm IG5 High-pressure ionisation chamber volume: 5,2 l active gas: Ar or H (20 bar) voltage: 400 V high-voltage: 1200 V 6

7 Set-up in the CERF Target Area (PMIs) SPS secondary hadron beam is hitting a copper target irradiation of the PMI chambers with different radiation fields at various positions. Pos 1 Pos 2 Pos 3 Pos 4 Pos 5 Pos 6 Beam parameters: Momentum: 120 GeV/c Hadron beam Cu target Intensity: 9*107 hadrons/ SPS cycle (16.8 s with 4.8 s continuous beam) Composition: 60.7% π % p 4.5% K + 7

8 Simulation of Particle Fluences Pos 6 Pos E-3 1E-4 Position 2 neutrons photons ch. hadrons e + /e - os 4 Pos 3 Pos 2 Pos 1 dφ/dln(e) 1E-5 1E-6 1E-7 1E-8 beam 1E-9 1E-4 1E Energy (GeV) 8

9 Simulation of Particle Fluences Pos 6 Pos E-3 Position 4 neutrons photons ch. hadrons e + /e - 1E-4 os 4 Pos 3 Pos 2 Pos 1 dφ/dln(e) 1E-5 1E-6 1E-7 1E-8 beam 1E-9 1E-4 1E Energy (GeV) 9

10 Simulation of Particle Fluences Pos 6 Pos E-3 Position 6 neutrons photons ch. hadrons e + /e - 1E-4 os 4 Pos 3 Pos 2 Pos 1 dφ/dln(e) 1E-5 1E-6 1E-7 1E-8 beam 1E-9 1E-4 1E Energy (GeV) 10

11 cm E August EPAC Doris Forkel-Wirth 11 cm 2.3E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E E-14 Simulated Dose Distribution Dose (average within ±10 cm) given in Gy per primary particle hitting the target. The circles indicate the positions of the chambers. 1 pc = 10 ngy deposited in active volume

12 Contribution of the Different Particle Types to the Energy Deposition neutrons photons el+pos ch_had muons others 30 August Pos Pos2 EPAC 2004 Pos3 - Doris Forkel-Wirth Pos4 Pos5 Pos6 12 % of count rate

13 Comparison simulation and experiment Simulation Counts/ prim. part. *10-6 Simulation error *10-6 Measurement Counts/ prim. part. *10-6 Measurement error *10-6 Simulation/ Error Measurement Pos 1 5,63 ± 0,12 5,64 ± 0, ± Pos 2 16,06 ± 0,44 15,58 ± 1, ± Pos 3 67,46 ± 0,73 67,25 ± 6, ± Pos 4 85,33 ± 0,64 79,00 ± 8, ± Pos 5 96,20 ± 1,26 89,39 ± 9, ± Pos 6 108,31 ± 0,82 115,74 ± 17, ±

14 The IG5 at CERF CS2 CT6/T10 CT4 CS-50U 80 cm of concrete between detector and target 14

15 Particle fluence at CT6/T10 1.E-04 1.E-05 kaons pion- protons pion+ Total neutronscontribution to response (Ar) photons d Φ / d ln(e) [1/cm 2 ] 1.E-06 1.E-07 1.E-08 1.E-09 Neutron Proton π γ (30 ± 1)% (24 ± 3)% (11 ± 1)% (35 ± 4)% Total contribution to response (H) Neutron Proton π γ (59 ± 3)% (17 ± 2)% (4 ± 1)% (20 ± 2)% 1.E-10 1.E-09 1.E-08 1.E-07 1.E-06 1.E-05 1.E-04 1.E-03 1.E-02 1.E-01 1.E+00 1.E Energy [GeV]

16 Comparison simulation & experiment for IG Ar - detailed H - detailed Ratio simulation/experiment CS2 CT6/T10 CT4 CS-50U 16

17 Dose Measurements in Pulsed Fields neutrons muons protons pions kaons electrons positrons photons Created charge Absorbed dose -> charge due to ionisation Signal, measured charge Problem in case of short pulses: Recombination effects (charge loss) Underestimation of absorbed dose Detector PS LHC injection 21.6s LHC 1.2 s 17

18 Recombination effects Ionisation chambers exposed to pulsed, high energy mixed radiation fields: AD: up to 50 mgy/pulse PSB: up to 160 µgy/pulse Proton beam Beam Dump PSB 18

19 Recombination effects Absorbed dose per pulse, measured (µgy) PTW type Centronic IG5-A20 Ar Absorbed dose per pulse, real (µgy) Air Efficiency Ar PTW type 34031, calculated PTW type 34031, measured Centronic IG5-A20, calculated Centronic IG5-A20, measured Absorbed dose per pulse (µgy) Air 90 % ion collection efficiency level Experiment agrees well with recombination model of W. Boag (ICRU 34) for air and H (the model is not applicable for Ar) Ar ~ 15 µgy/pulse H ~ 250 µgy/pulse Air ~ 50 µgy/pulse 19

20 Read-Out Electronics For pulsed fields the read-out electronics has to be based on charge digitizers Range to be covered: A (background level) A Switching not permitted! Input (charge) charge buffer Integrator Charge pump Comparator Control circuitry Output signal (frequency) Present CERN electronics covers 5 6 decades Threshold Low charge injection switch Newly developed: 9 10 decades Input (charge) Integrator Adaptive digitizer Processor Output signal (fieldbus) First tests: electronics measures reliably up to 300 nc/pulse ~ 50 mgy/hour (LHC injection) 20

21 Conclusion Response of ionisation chambers to pulsed, mixed high energy radiation fields is very well understood Detector response to LHC radiation fields can be extrapolated by Monte Carlo simulations Studies will be used to define RP standards in the field of radiation ation monitoring around particle accelerators Adequate read-out electronics is developed to cover a wide measuring range Pulse per pulse data locking possible Air filled plastic ionisation chambers can be used for on-line monitoring of high doses inside the tunnel or the experiments Further studies: optimisation of the detector design by Monte Carlo C simulations (variation of fill gases, walls ) All radiation protection competencies, experience and tools exist t to survey properly the LHC 21