Stefania Trovati EPFL - CERN S. Trovati - SATIF 101

Outline  Beta-beams  Decay ring  Activation studies: residual dose rates ○ collimation section ○ arcs airborne activity S. Trovati - SATIF 102

EURISOL Beta-beams (CERN, IPNO, CEA, GSI, MSL) Neutrino Source Decay Ring Ion production ISOL target & Ion source Proton Driver SPL SPS Acceleration to medium energy RCS PS Acceleration to final energy PS & SPS Experimen t Ion acceleration Linac Beam preparation Pulsed ECR Ion productionAccelerationNeutrino source 3

Objectives & Methods  Radiological risk assessment for the beta-beam facility at CERN: full evaluation of all radiation protection aspects of the machines  feasibility at CERN.  Problem: no available experimental data for 18 Ne and 6 He  Monte Carlo calculations, carefully…  MC calculations for prompt radiation and induced activity studies: shielding design for tunnels, residual doses and airborne doses.  MC code: FLUKA with BME  nucleus-nucleus interactions below 100 MeV/u. S. Trovati - SATIF 104

30 o 60 o 5 Comparison study between data and FLUKA with BME 20 Ne -> Copper 100 MeV/u (T. NAKAMURA et al., “Measurements of secondary neutrons produced from thick targets bombarded by high energy Neon ions”, J. Nucl. Sci. Tech., 36, 42 (1999))

The Decay Ring (DR)  Primary beams: 6 He and 18 Ne ions at ~92 GeV/u.  Decay losses in bumps and arcs (  ± decays).  Collimation losses in the collimation section.  Total number of decays/s in the DR: Loss maps: calculated by ACCSIM code. For collimation by ACCSIM+FLUKA. S. Trovati - SATIF 10 Same length as SPS m injection 602 m 2510 m Collimation section bumps 6 He/s: 1.6 E Ne/s: 2 E+13 6

Residual dose rates during maintenance  The beta-beam facility will work for 10 7 seconds  3 months.  Irradiation cycle: 3 month irradiation followed by 1 hour, 1 day, 1 week waiting times.  The residual H*(10) rate in  Sv h -1 scored along the tunnel.  MC calculations: electromagnetic cascade off in prompt radiation, on in decay.  Radionuclide yields estimated. S. Trovati - SATIF 107

Collimation section and bumps  The collimation section stays in between the two bumps and foresees the combination of a primary and two secondary collimators, all made of carbon. In between the collimators and all along the section there are several carbon absorbers. Collimators Bump area S. Trovati - SATIF 108

Bump areas: magnet geometry in FLUKA Magnet layouts from SESAME. Different lengths  different masses Quadrupole: 2 m long Dipole: 12 m long Beampipe: 8 cm aperture hor., 1.5 cm vert., 1mm thick. 76 cm 45.3 cm 4 cm 20 cm S. Trovati - SATIF 109

2 nd BN3 in the first bump  dipole+quadrupole+ long straight section  25 m 2 nd BN3 BN2 BN3 QQ Q Q Q Q Q ~10 10 parts s -1 over 25 m QQ S. Trovati - SATIF 1010

6 He After 1 hour After 1 day After 1 week S. Trovati - SATIF 1011 The dose rate doesn’t change much between a 1-day and a 1-week waiting

Dominant residual radionuclides and their specific activities in the bump magnets Pipe RadionuclideA (Bq g -1 ) Cr E+05 Mn E+05 V E+04 Mn E+04 Sc E+04 Mn E+04 Sc-44m2.50E+04 Ti E+04 Ni E+04 Co E+04 Na E+03 Yoke RadionuclideA (Bq g -1 ) Cr E+05 V E+05 Mn E+05 Mn E+05 Mn E+05 Fe E+05 Sc E+05 Ti E+04 Co E+04 Coils RadionuclideA (Bq g -1 ) Cu E+05 Co E+05 Cr E+04 Co E+04 Co E+04 Co E+04 V E+04 Mn E+04 Mn E+04 Mn E+04 Ni E+04 Sc E+04 Ni E+04 S. Trovati - SATIF 10 after 1 hour for 6 He 12

Summary 1h 1d 1w 6 He 18 Ne 6 He 18 Ne 6 He 18 Ne 1 st Q- 1 st BN nd Q rd Q - 1 st BN th Q nd BN3 - 7 th Q nd BN2 - 9 th Q S. Trovati - SATIF 10 BN2 BN3 QQ Q Q Q Q Q Q Q Dump before 2 nd BN3 – 7 th Q and 2 nd BN2 – 9 th Q Dump before 2 nd BN3 – 7 th Q and 2 nd BN2 – 9 th Q 13 Dumps

Collimation section: 18 Ne S. Trovati - SATIF 10 > 100 mSv h After 1 week the residual dose around the primary collimator is still above the prohibited area limit. Power deposited in quadrupoles after the primary collimator  absorbers required, decrease of factor 4 on average Courtesy of E. Bouquerel

Arcs  Arcs are composed of cold magnets, LHC- like.  A large aperture allows to avoid losses in the straight sections (ss) BUT high power deposited in the first dipole in the arcs (10 W/m in ss)  dumps.  Worst case study here, with no dumps.  Two configurations under study to avoid magnet quench and high induced activity absorbers between the magnets open mid-plane magnets S. Trovati - SATIF 1015

Arcs Case 1: layout for coils in the absorber configuration For dipoles: copper wedges implemented separately from cables. For quadrupoles: compound material that includes copper wedges into cables. Yoke material composition: 98% iron, 1% nichel, 0.4% manganese, 0.1 % silicon, 0.1% carbonium, 0.2 % copper. *Courtesy of F. Cerutti ( specifications by J. Miles - N. Mokhov) * S. Trovati - SATIF 1016 C. Hoa M. Mauri

Arcs Case 2: open mid-plane magnets and no absorbers S. Trovati - SATIF 10 Aluminum absorbers in the mid-plane 17

ARC DIPOLES & QUADRUPOLES Design by J. Bruer Dipole length: m Quadrupole length: 2 m Absorber length: 1 m Absorber material: steel S. Trovati - SATIF 1018

6 He: with absorbers 18 Ne: with absorbers 6 He: without absorbers 18 Ne: without absorbers Residual dose rates in the arcs with absorbers or with open mid-plane dipoles. mSv h -1 6 He 18 Ne 1 hour1 day1 week1 hour1 day1 week With absorbers Open mid- plane dipoles S. Trovati - SATIF 10  Sv h -1 19

Airborne activity  Limits for airborne activity: Swiss directive HSK-R-41.  0.2 mSv maximum annual Effective Dose for inhalation.  For CERN 10 μSv y -1 for all the installations.  1 μSv y -1 is assumed for each machine in beta-beam complex.  Conversion coefficients Bq->Sv from CERN-SC IE-TN.  Reference population group: 240 m from the stack (ISOLDE stack).  Outdoor and indoor exposures are weighted according to occupancy factors. S. Trovati - SATIF 1020

Methods  Air activity: FLUKA simulations: n, p,    track length spectrum scoring in the air tunnel. Off-line folding of particle track-length spectra with isotope production cross sections: n j = atomic concentration (per cm 3 ) of the element j in the material  ijk = cumul. cross section for the nuclide i in the reaction of a particle of type k and energy E with a nucleus of element j  k = track length sum of hadrons of type k and energy E  Analytical model for the air diffusion in the tunnel, through the ducts. S. Trovati - SATIF 1021 Φ F A surface Vol l

 The dominating reaction channels are: Half-life < 1day: ○ 11 C (spallation on N and O): 14 N(p,  ) 11 C, 14 N( ,  H) 11 C. ○ 13 N reactions on nitrogen: (n,2n). ○ 14 O: (p,n) on nitrogen, neutron removal on oxygen. ○ 15 O (reactions with oxygen, especially neutron removal): (n,2n), ( ,2n). ○ 41 Ar (low-energy neutron capture on argon). Half-life > 1 day: ○ 7 Be (spallation by high energy reactions on N (most) and O): reactions on Ar play a minor role. ○ Cl spallation on argon dominated by neutrons. S. Trovati - SATIF 1022

Airborne activity in DR RadionuclideHalf-life Annual dose (  Sv) Ar-41hours6.94E-03 N-13minutes1.26E-03 C-11minutes1.60E+00 Be-7months3.88E-01 O-15minutes9.27E-01 Cl-39minutes3.54E-03 Cl-38minutes6.16E-02 P-32days1.38E-01 Na-24hours3.47E-03 O-14seconds9.29E-03 6 He case. F = m 3 h -1 Tunnel volume = m 3 Exit duct volume = 300 m 3 The total annual dose is of 4.5  Sv ISOLDE conversion coefficients S. Trovati - SATIF 1023

Airborne activity in DR RadionuclideHalf-life Annual dose (  Sv) Ar-41hours1.50E+00 N-13minutes1.43E+00 C-11minutes1.36E+00 Be-7months5.89E-01 O-15minutes2.52E-01 Cl-39minutes1.86E-01 Cl-38minutes8.12E-02 P-32days7.71E-02 Na-24hours5.63E-02 O-14seconds2.07E Ne case. F = m 3 h -1 Tunnel volume = m 3 Exit duct volume = 300 m 3 The total annual dose is of 5.6  Sv ISOLDE conversion coefficients S. Trovati - SATIF 1024

Conclusions  Released airborne activity is within Swiss constraints, but above assumed limits for CERN machines.  Area classification according to CERN: limited stay controlled area to high radiation area, accessible after 1 week or more depending on the position.  Dumps before the arcs are needed.  Remote handling during maintenance for the collimator area.  Need for experimental data for comparisons! S. Trovati - SATIF 1025

II. Safety code F, classification of areas and personnel Radiation areas: classification Occupationally exposed workers: Class A> 6 mSv / 12 months Class B< 6 mSv / 12 months S. Trovati - SATIF 1026