CERF Benchmark Study of Radionuclide Production with FLUKA M. Brugger on behalf of the CERN-SLAC RP Collaboration

31st August 2006 CERF Benchmark Study of Radionuclide Production with FLUKA 2 Motivation For Experiments

31st August 2006 CERF Benchmark Study of Radionuclide Production with FLUKA 3 Motivation Beamline components at high-energy hadron colliders can become highly activated due to various beam loss mechanisms. The activation of components and equipment is an important radiation safety concern during the operation of facility: dose to personnel during maintenance interventions decommissioning of facility and disposal of activated materials Rather accurate calculations of the radionuclide inventory are required in order to avoid unjustified doses to personnel and environment during operation due to underestimates in the design phase excessive costs (e.g., for waste disposal) caused by overly conservative estimates Modern Monte Carlo codes (FLUKA) allow a detailed assessment of isotope production by high-energy particle beams. However, processes and methods involved are very complex and benchmark studies are essential.

31st August 2006 CERF Benchmark Study of Radionuclide Production with FLUKA 4 CERN – Accelerators Injectors SPS Extraction North Experimental Hall H6 Beamline

31st August 2006 CERF Benchmark Study of Radionuclide Production with FLUKA 5 CERF

31st August 2006 CERF Benchmark Study of Radionuclide Production with FLUKA 6 CERN-EU High-Energy Reference Field (CERF) facility Location of Samples: Behind a 50 cm long, 7 cm diameter copper target, centered with the beam axis

31st August 2006 CERF Benchmark Study of Radionuclide Production with FLUKA 7 Target Setup Samples were placed downstream and lateral to the CERF copper target (50cm long, 7cm diameter) A custom built holder ensured a quick exchange of the samples and a correct alignment with the target The induced radioactivity in the target itself was also determined using a mobile Gamma Spectroscopy instrument and a proper analysis software, so to account for its dimensions as well as the angle and distance to the detector

31st August 2006 CERF Benchmark Study of Radionuclide Production with FLUKA 8 Beam Conditions 120 GeV secondary SPS mixed hadron beam (p 34.8%,  60.7% and  4.5%) 16.8s spill cycle, 4s burst ~ 5 x10 10 (short) - 1 x10 12 (long) particles hit the target during irradiation Particles hitting the target were measured using a Precision Ionization Chamber ~ 1x10 8 particles/spill ~ 6x10 6 particles/second Beam Profile (approx. Gaussian): measured with multi-wire prop. Chamber,  ~ 10 mm

31st August 2006 CERF Benchmark Study of Radionuclide Production with FLUKA 9 Details of Samples Large variety of samples (typical for the LHC) Different irradiation times  Short (~ 8 hours)  Long (~ 1 week) Different locations during the irradiation  downstream  lateral Various measurements at different cooling times

31st August 2006 CERF Benchmark Study of Radionuclide Production with FLUKA 10 Chemical Composition

31st August 2006 CERF Benchmark Study of Radionuclide Production with FLUKA 11 Gamma Spectrometry Low background coaxial High Precision Germanium detector Canberra: two different detectors 90 cm 3 sensitive volume, 60% and 40% relative efficiency at 1.33 MeV Genie-2000 (Ver. 2.0/2.1) spectroscopy software by Canberra and the PROcount-2000 counting procedure software include a set of advanced spectrum analysis algorithms: e.g. nuclide identification, interference correction, weighted mean activity, background subtraction and efficiency correction. comprise well-developed methods for peak identification using standard or user- generated nuclide libraries High accuracy for the measurements is achieved via regular quality assurance Use of user-generated nuclide libraries, based on nuclides expected from the simulation and material composition Manual revision of results in case ambiguities (overlapping peaks, contributions from different isotopes, etc.)

31st August 2006 CERF Benchmark Study of Radionuclide Production with FLUKA 12 Dose Rate Measurements Portable spectrometer Microspec (Bubble Technologies Ind.)  NaI detector, cylindrical shape, 5 x 5 cm  sensitivity between 60 keV and 3 MeV  dose rates (H*(10)) up to 100  Sv/h  folds spectrum with detector response (“calibrated” with 22 Na source)  physical centre of detector determined with additional measurements with known sources ( 60 Co, 137 Cs, 22 Na) to be 2.4 cm Thermo-Eberline dose-meter FHZ 672  organic Scintillator and NaI detector, cylindrical shape, 9 x 9 cm  H*(10) covering a range from 48 keV to 6 MeV  dose rates up to 100  Sv/h  assumes average detector response  physical centre of detector determined as above to be 7.3 cm

31st August 2006 CERF Benchmark Study of Radionuclide Production with FLUKA 13 First Step:  simulation of isotope production by high-energy processes and low-energy neutron interactions  calculation of build-up and decay of radioactive isotopes for arbitrary irradiation pattern and cooling times including radioactive daughter products  storage of information on produced radionuclides in an external file (mass, charge, position of creation, activity, weight) Second Step:  sampling of photons, electrons, and positrons from radioactive decay assuming isotropic emission and taking into account correct branching ratios, intensities and energy spectra (positrons and electrons, obtained from program NUCDECAY)  simulation of the electromagnetic cascade induced by these particles, e.g., in the beamline and shielding components or in air  calculation of dose equivalent rate by folding fluence with energy-dependent dose equivalent conversion factors, at any points of interest The calculation of residual nuclei and dose rates is also available as one step method implemented in FLUKA, however for the benchmark it is necessary to change the geometric configuration between the calculation of the radioisotopes and the residual dose rates which is only possible in the two step approach. FLUKA Simulations

31st August 2006 CERF Benchmark Study of Radionuclide Production with FLUKA 14 Particle Spectra at Sample Positions Copper Sample downstream of target Aluminium Sample laterally to target forward direction, thus dominant  +,  - lateral spectra, but close to the target, thus dominant 1MeV n

31st August 2006 CERF Benchmark Study of Radionuclide Production with FLUKA 15 Aluminium Sample Cooling Times: (4) 25m and (5) 1h 09m, (1) 1d 16h 55m, (2) 16d 8h 56m, (3) 51d 9h 47m FLUKA Old 0.36 high Exp. Error! very short half-life, thus unc. in EOI

31st August 2006 CERF Benchmark Study of Radionuclide Production with FLUKA 16 fragmentation A>24 Copper Sample Cooling Times: (1) 34m (2) 1h 7m (3) 2d 5h 28m (4) 48d 3h 21m FLUKA Old 0.05 problem in GS ( 48 Sc, 48 V) very short half-life, thus unc. in EOI 50/50% assumption GS ( 65 Ni, 65 Zn) FLUKA xSection

31st August 2006 CERF Benchmark Study of Radionuclide Production with FLUKA < R < < R ± Error < 1.2 Ratio FLUKA/Exp R + Error < 0.8 or R – Error > 1.2 Exp/MDA < 1 Example: CERF Isotope Production

31st August 2006 CERF Benchmark Study of Radionuclide Production with FLUKA 18 Iron – Dose Rates A very good agreement can be observend for the Microspec Instrument For the Eberline instrument only few data points are available  As for the observed systematic discrepancy for the Eberline instruments, this can most probably explained by: measured data below 10 nSv/h were excluded from graphs (except for Al) its varying energy response with respect to the calibration using Cs137 its calibration in homogenous fields at large distances (under investigation)

31st August 2006 CERF Benchmark Study of Radionuclide Production with FLUKA 19 Aluminium – Dose Rates Good agreement for the Microspec Instrument Positrons annihilate in the sample and contribute to dose rate via the two 511 keV photons ( only at short cooling times t c < 1h) Errors of Measurements include the following:  ± 2 mm of the effective centre of the detector as well as the positioning of the samples  Eberline: a statistical error obtained from repetitive measurements  Microspec: 5% general uncertainty as specified in the manual  a systematic instrument uncertainty of 1 nSv/h

31st August 2006 CERF Benchmark Study of Radionuclide Production with FLUKA 20 Concrete – Dose Rates  Again good agreement for the Microspec instrument  the Eberline instrument shows systematically higher values, however the effect is bigger after 2 hours of cooling, where different isotopes dominate contributing Isotope?

31st August 2006 CERF Benchmark Study of Radionuclide Production with FLUKA 21 Concrete Contribution Gamma vs. Beta+ Emitter Beta + emitters are dominant up to 2 hours of cooling gamma Emitter!

31st August 2006 CERF Benchmark Study of Radionuclide Production with FLUKA 22 Concrete - Contributors Contribution of gamma and positron emitting isotopes to total dose rate at 12.4 cm Assumption: sample is point-source of photons (2 x 511keV in case of positrons) dD A(t c ) ∑ I  E  dt 7 r 2 x = 24 Na: Ratio ~ 0.7

31st August 2006 CERF Benchmark Study of Radionuclide Production with FLUKA 23 Parent Reactions Al Cu directly producedpartl. coming from Parents

31st August 2006 CERF Benchmark Study of Radionuclide Production with FLUKA 24 sign. lowEn. Neutron Production Production Al Cu mainly  -production also significant p/n production

31st August 2006 CERF Benchmark Study of Radionuclide Production with FLUKA 25 7 Be from Aluminium Ratio calculated / measured activity: default evaporation 0.36 new evaporation 0.71 Response (arbitrary units)

31st August 2006 CERF Benchmark Study of Radionuclide Production with FLUKA Mn from Copper FLUKA/Exp: default evaporation 1.18 new evaporation 1.19

31st August 2006 CERF Benchmark Study of Radionuclide Production with FLUKA 27 Downstream: Laterally: - Dominated by high energy hadrons with energies above ~5 GeV - Sensitive to Cross Section above Threshold (~16mb) - Cross Section Overestimated (?) by FLUKA - Mainly Produced by Hadrons with Energies of a few GeV - Very Sensitive to the Cross Section at the Production Threshold - Well Reproduced by FLUKA “Response” Test Case: Be7 on Cu

31st August 2006 CERF Benchmark Study of Radionuclide Production with FLUKA 28 Confirmed by Cross Section Data ! Overestimated (?) Slightly Underestimated Test Case: Be7 on Cu

31st August 2006 CERF Benchmark Study of Radionuclide Production with FLUKA 29 Par. 1)  The simulation is always right Par. 2)  In case of measurements deviating from the simulation results refer to Par. 1) Par. 3)  In the immediate urge of publications scale the measured values accordingly The Four Laws of MC Simulations Par. 4)  !!! DO NOT TELL !!!

31st August 2006 CERF Benchmark Study of Radionuclide Production with FLUKA 30 Conclusions The FLUKA code allows one to calculate in detail induced radioactivity and residual dose rates for arbitrary materials and configurations. The predictions given by FLUKA were benchmarked with experimental data. Agreement was found to be within 20% in most cases. A detailed comparison with xSection data and reaction channels is mandatory in order to understand the origin of uncertainties or disagreements between measurements and simulations. As a result radionuclide inventories and residual dose rates can be predicted in detail. Currently a new approach of modelling the high-energy hadron-nucleus part in FLUKA is in its testing phase, extending PEANUT to energies > 5 GeV