F. Cerutti 1 , N. Charitonidis 1,2 and M. Silari 1 1 CERN, 1211 Geneva 23, Switzerland

1. Neutron double differential distributions, dose rates and specific activities from accelerator components irradiated by 50 – 400 MeV protons F. Cerutti1, N. Charitonidis1,2 and M. Silari1 1CERN, 1211 Geneva 23, Switzerland 2 Department of Physics, National Technical University of Athens, Zografou Campus, 157 80 Athens, Greece SATIF-10, 2-4 June 2010, CERN, Geneva, Switzerland

2. Scope • Activation data concerning the materials involved in CERN experimental facilities are rather specific • Systematic Monte-Carlo simulations with the FLUKA code using a simplified geometry were performed • The ambient dose equivalent rate, the residual nuclei inventory as well as the neutron spectra were scored for 5 common accelerator materials for proton energies in the 50 - 400 MeV range • The results of the present study aim to provide a simple database for a first estimate of the radiological risk SATIF-10, 2-4 June 2010, CERN, Geneva, Switzerland

3. Simulation set-up • 2 sets of simulations with the same, simplified geometry • 1st: Residual nuclei inventory in the target and ambient dose equivalent around the target, up to 1 meter distance, after 7 different cooling times • 2nd: Prompt neutron spectra escaping from the target The effect of a concrete tunnel around the target was studied with a special set of simulations SATIF-10, 2-4 June 2010, CERN, Geneva, Switzerland

4. Irradiation Profile: 9 months constant irradiation, 6E12 p/s or 1 µA beam current Geometry Right, solid cylinders 50MeV H=1.34cm H=0.46cm H=0.50cm 250MeV H=23.04cm H=7.50cm H=8.18cm 400MeV H=50.04cm H=16cm H=17.6cm SATIF-10, 2-4 June 2010, CERN, Geneva, Switzerland

5. Ambient dose equivalent as a function of the distance Stainless Steel – Cooling time 1 day ~ 10-20 mSv/h ~ 40-50 mSv/h 50MeV 100MeV ~ 500 – 800 mSv/h ~ 800 – 1000 mSv/h ~ 50 – 100 mSv/h 400MeV ~ 100-200 mSv/h 200MeV ~ 1000-1500 mSv/h >1300 mSv/h

6. Ambient dose equivalent as a function of the distance Stainless Steel – Cooling time 3 months 50MeV ~ 2-10 mSv/h 100MeV ~ 5-10 mSv/h ~ 100-300 mSv/h ~500-800 mSv/h ~ 6-7 mSv/h 200MeV ~ 9 – 12 mSv/h 400MeV ~ 500 – 700 mSv/h > 80 mSv/h

7. Ambient dose equivalent rate as a function of cooling time BN Cu SS

8. Self absorption The slope does not change accordingly to the width of the target

9. Radionuclide Inventory SATIF-10, 2-4 June 2010, CERN, Geneva, Switzerland

10. Prompt neutron yield(escaping from the target) • The neutron double differential yield was scored in 6 angular bins on the target boundary (0o - 15o, 15o - 45o, 45o - 75o, 75o - 105o, 105o – 135o and 135o - 180o) with respect to the beam axis • Same geometry, same energy range, same materials • Importance biasing to compensate for the attenuation of low energy neutrons SATIF-10, 2-4 June 2010, CERN, Geneva, Switzerland

11. Neutron Spectra Copper Total Yield: Total Yield: 100MeV 400MeV Carbon 100MeV Total Yield: Total Yield: 400MeV

12. Effect of concrete tunnel • The effect of a concrete tunnel around the target was examined • The tunnel was modeled as a concrete sphere enclosing the target • The material chosen was Iron, and the beam energy chosen was 400MeV • The escaping neutron spectra, as well as the ambient dose equivalent was scored SATIF-10, 2-4 June 2010, CERN, Geneva, Switzerland

13. Effect of concrete tunnel Tunnel’s width=1m Tunnel’s height: 2m SATIF-10, 2-4 June 2010, CERN, Geneva, Switzerland

14. Ambient dose equivalent Increase of H*(10) due to concrete activation and thermal neutrons production increase (target activation)

15. Neutron population 5 orders of magnitude !

16. Conclusions • An evaluation of the radiological risk through a simple database • Critical role of the neutron thermalisation on the tunnel’s concrete and its effect on ambient equivalent dose • Ongoing study for calculations of the same quantities with the presence of the wall SATIF-10, 2-4 June 2010, CERN, Geneva, Switzerland

17. Thank you !