C. Theis, D. Forkel-Wirth, S. Roesler, H. Vincke

Outline  Ambient-dose-equivalent studies for  An accident scenario (full beam-loss)  Normal operation  Calculation of field calibration coefficients for the IG5 ionization chambers RAMSES monitoring system. 2 C. Theis, SC/RP

Motivation  Previous radiation studies by S. Roesler et al. date back >5 years already.  Minimum requirements for openings were 3m in the lower & 2m for the upper shielding.  Shielding layout has changed (new ducts, access maze, etc.)  Check compliance with radiation limit of 20 mSv ambient-dose-equivalent for a full beam loss (~ 20 mSv effective-dose) 3 C. Theis, SC/RP

FLUKA geometry C. Theis, SC/RP 4 LHCb shielding wall Counting barracks Entrance maze Beam tunnel Barrack Access shaft PX84 Y Z X 2m Entrance maze (shown without roof) 4m Cable tray in the floor (1.1 x 0.17 m) 3m Side slit for cables (0.4 x 5.6m) Ventilation ducts Material passageway (blocked during operation) PAXL8501 PAXL8502 PAXL8511 PAXL8521 PAXL8512 PAXL8522 Front part of the counting barracks

Beam-loss scenario  Full loss of 1 beam  Protons at 7 TeV/c  Loss at the worst location, giving the highest particle fluence in the cavern (5m upstream from the center of the cavern)  2 - step calculations  1 st step without the electromagnetic cascade  2 nd step including the electromagnetic cascade C. Theis, SC/RP 5

Beam-loss scenario C. Theis, SC/RP 6 Beam loss point Loss direction Beam loss point Loss direction Hadrons caused by the beam-loss :poss Beam loss point Loss direction Material passage is in the “shadow” at a full beam-loss Direction of the high-energetic particles

Beam-loss scenario C. Theis, SC/RP 7 Ground floor of the barracks Limits: (4.7 x protons) Red arrow ~ 50 mSv Blue arrow ~ 20 mSv pSv/primary Y Z PAXL8501 PAXL8502 Front part of barracks pSv/proton No significant impact of the cable tray in the floor Avg. value for the front part of the barracks ~ 4mSv

Beam-loss scenario C. Theis, SC/RP 8 2 nd floor of the barracks Limits: (4.7 x protons) Red arrow ~ 50 mSv Blue arrow ~ 20 mSv Y Z pSv/primary PAXL8521 PAXL8522 Front part of barracks pSv/proton Worst location 7.24 mSv

Beam-loss scenario C. Theis, SC/RP 9 Center of the cavern Y X pSv/primary Front part of barracks pSv/proton Limits: (4.7 x protons) Red arrow ~ 50 mSv Blue arrow ~ 20 mSv Avg. value for the front part of the barracks ~ 4mSv

Normal operation  DPMJET 3 for 7 TeV proton-proton collisions  FLUKA for particle transport  2 step-method like for the beam-loss scenario  Normalization parameters:  Luminosity L = 2 x cm -2 s -1   = 80 mbarn  Beam-gas interactions (10 4 collisions/s) were neglected C. Theis, SC/RP collisions/s

Normal operation C. Theis, SC/RP 11 Y Z  Sv/hour PAXL8501 PAXL8502 Front part of barracks  Sv/h Ground floor of the barracks Limits: Blue arrow ~ 3  Sv/h Average value for the front part of the barracks ~ 5.6 x  Sv/h ± 2%

Normal operation C. Theis, SC/RP 12 2 nd floor of the barracks Limits: Blue arrow ~ 3  Sv/h Worst location ~ 0.1  Sv/h ± 7% Y Z PAXL8521 PAXL8522 Front part of barracks  Sv/hour  Sv/h

Normal operation C. Theis, SC/RP 13 Y X  Sv/h our Front part of barracks  Sv/h Center of the cavern Limits: Blue arrow ~ 3  Sv/h Average value for the front part of the barracks ~ 5.6 x  Sv/h ± 2%

Field calibration studies Up to 6 IG5-H20 hydrogen filled ionization chambers will be installed. Usually calibrated with 238 PuBe source (neutrons up to 11 MeV) at LHCb there is a field calibration mixed field with much higher energies field calibration C. Theis, SC/RP 14 PAXL8501 PAXL8502 PAXL8511 PAXL8521 PAXL8512 PAXL8522 Front part of the counting barracks

Field calibration procedure C. Theis, SC/RP 15 1 Calculate monitor response function (charge per unit fluence) 2 Calculate particle fluence spectra at monitor location Calculate ambient-dose-equivalent (Sievert per unit fluence) 3 Convolve response and fluence spectra (total charge per unit fluence) 4 Field calibration factor = calculated Sievert / calculated total charge in the ionization chamber

Typical mixed field spectrum C. Theis, SC/RP 16 Average mixed field spectrum for the frontal barracks Spectrum for PAXL8522 Frontal barracks Individual factors would be the optimum solution.

Field calibration factors C. Theis, SC/RP 17 LocationCalibration factor [nSv/pC] Barrack8.11 ± 2% PAXL ± 7% PAXL ± 6% PAXL ± 5% PAXL ± 6% PAXL ± 7% PAXL ± 7% Individual values deviate from the one that was calculated as an average over the frontal barrack area by 20% individual values would be best.

Comparison to 238 Pu-Be calibration C. Theis, SC/RP 18

Field calibration vs. 238 PuBe  Agreement within ~25% for fields that are comparable to LHCb or the CERF facility.  However, the agreement comes from the integral compensation due to other particles. The charge due to neutrons only would underestimate the dose! C. Theis, SC/RP 19

Neutron response of the IG5-H20 chamber in a CERN-typical neutron spectrum C. Theis, SC/RP PuBe has a mean energy of ~4.5 MeV. Compared to this the response to high- energy neutrons (>20 MeV) is much lower and thus, the contribution of these particles in a typical mixed field outside some concrete shielding, would be underestimated.

Summary & conclusions  The final shielding design was found to be compliant with the old minimum shielding requirements.  Neither the accident scenario nor the normal operation should not exceed the tolerable limits. C. Theis, SC/RP 21

IG5-H20 response functions C. Theis, SC/RP 22