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Optimization Studies for Neutron Target and Shielding at n_TOF Collaboration Meeting

This report summarizes the results of detailed geometry simulations and optimization studies presented during the N_TOF Collaboration Meeting held from November 28-30, 2012. Key topics include improvements for the spallation target and neutron moderator design aimed at enhancing neutron flux and resolution, as well as evaluations of dose reduction techniques in the ISR tunnel. It covers the introduction of collimators for background reduction, activation calculations for the current neutron setup, and future target optimization requirements to maximize efficiency and safety.

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Optimization Studies for Neutron Target and Shielding at n_TOF Collaboration Meeting

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  1. n_TOF EAR2 Simulation Studies N_TOF Collaboration Meeting I.Bergstrom, J.Mann, J.Vollaire, C.Weiss, T.Zhang, V.Vlachoudis 28-30 Nov 2012

  2. Geometry • Detailed Geometry • C.Weiss • I. Bergstrom • J. Volaire • J. Mann • T. Zhang

  3. Spallation Target • Neutron moderator • Beam pipe layout • Fluence and resolution estimation • Dose to electronics • Optimization of the neutron target for future upgrade • Determination of neutron gain by shifting the vertical pipe to neutron maximum • Activation calculation of the present spallation target, container for a possible decommissioning in 2018 Neutron pipe Moderator Spallation target Container

  4. Neutron Fluence Maximum Gain: 27 (keV Region) Reference for EAR1 : FLUKA Simulations with fission collimator (d = 8 cm) C.Weiss

  5. Neutron Moderator • Simulations have been performed for a setup: • Without additional moderator at the bottom of the neutron tube • With Moderator at the bottom of the tube: Polyethylene (dmin = 1 cm) C.Weiss

  6. Resolution in comparison with EAR1 Neutron Fluence is reduced by about 32 % if a Moderator in this form isused * C. Coceva et al., NIMA 489 (2002) 346-356 C.Weiss

  7. Future target for 2018 • A more optimized target would require to cut the lead at Dz=16.5cm • Gain in flux ×2-4(Vertical flight path) • Loss of 20% in horizontal flight path • Gain in resolution since top surface is flat • Correct positioning of vertical neutron pipe would give an additional gain 10-20% Incompatible with the present target/layout. Will delay considerably the project! T.Zhang

  8. 1st Collimator, Magnet & Shielding • Introduction of 1st collimator: • Shaping the beam • Background reduction in ISR • Magnet protection • Permanent magnet • Field intensity needed • Dose (degradation of magnet) Permanent Magnet Additional Shielding For ISR 1st Collimator

  9. Magnet pmax = 1.205 [GeV/c] protons B = 0.2 [T] Possible Position for a magnet: Assumed magnet length: l = 1 [m] C.Weiss

  10. ISR Shielding • Dose reduction in ISR tunnel • Permanent work place< 0.5 mSv/h • Non-permanent work place< 2.5 mSv/h • Lot’s of constraints: • Keeping the existing crane • Amount of shielding • Existing cables/piping • n_TOF PS-line controls • Numerous shielding options have been evaluated • Introduction of 1st collimator Crane level ISR tunnel Existing Shielding

  11. Dose in ISR tunnel Default layout Safety factor ×3 & Future targetNot INCLUDED! With additional shielding + collimator I.Bergstrom

  12. 1stCollimator Test of various 1st collimators andimpact on the total neutron fluencein the experimental area  Chosen  No Collimator • Collimator: • 1m long made of iron • Internal diameter 190mm • Z=7 m from center of target I.Bergstrom

  13. Second Collimator, EAR, Neutron Dump • Preliminary study of Collimator • Capture • Fission setup • EAR-2 Background • Neutron dump • External wall • Shielding for the EAR2 walls and beam dump • Study of dose due to skyshine • Study of residual dose rate and air activation Neutron Dump External Wall ExperimentalArea 2nd Collimator

  14. Background in EAR2 • Beam profile and background in the area for fission setup (worst case) • WARNING: • 1st and 2nd collimator are not optimized • Beam dump is not optimizedfor back-scattering Non-optimized!4-5 ordersof magnitude

  15. Prompt dose rate (30 cm collimator) FLUKA geometry of the bunker Prompt dose – 30 cm collimator + new target (x3 intensity) Extra wall (30 cm collimator) J.Vollaire

  16. Dose due to skyshine (1 y operation) J.Vollaire

  17. Residual dose rate and air activation 5 min cooling time • Checking if activation of the beam dump in the EAR2 area could be a problem for access and additional measures are required • Irradiation cycle (very conservative) : • 5 consecutive years • 30 cm collimator(100 % of the time) • 9 Months with 1.59 109 n/sentering the area • Air activation is found negligible 8 hours 7 days J.Vollaire

  18. Summary A large amount of calculation has been performed, mainly focused on the facility and RP issues (thanks to Ida, Cristina, Joachim, Tian, Jonn) Pending Calculations • Magnet Sm-Co evaluation of the 60Co production • Air activation in the access gallery • Dose to earth, needed for RP during excavation • 1st and 2ndCollimator optimization • Materials of collimator and surrounding elements • Exchangeable setups Capture, Fission and Electronic testing • EAR-2 Background optimization (w/o samples and detectors) • Neutron dump backscattering, respecting the max weight of the dump imposed by Civil Engineering • “g-flash” from fast neutron on 2ndcollimator

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