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Response of Ionization Chambers to High-Energy Monoenergetic Neutrons

H. Vincke, D. Forkel-Wirth, H. G. Menzel, S. Roesler, C. Theis, M. Widorski, K. Hatanaka, H. Yashima, T. Nakamura, S. Taniguchi, N. Nakao, A. Tamii

Nuclear Technology / Volume 168 / Number 1 / October 2009 / Pages 5-10

Detectors / Special Issue on the 11th International Conference on Radiation Shielding and the 15th Topical Meeting of the Radiation Protection and Shielding Division (Part 1) / Radiation Protection /

Radiation monitoring during operation of CERN's high-energy accelerators in general, and the Large Hadron Collider and its experiments in particular, poses a major challenge due to the stray radiation fields, which are characterized by a complex particle composition and a wide range of energies. In order to monitor ambient doses around workplaces and inside the machine tunnel, high-pressure ionization chambers (so-called IG5) and air-filled ionization chambers under atmospheric pressure (PMI) will be used. Because of the complexity of the radiation field, standard gamma or neutron radiation sources are not applicable to accurately calibrate monitors used in such environments. Hence, the use of Monte Carlo simulation programs like FLUKA is indispensable to obtain an appropriate monitor calibration. Following this idea the response of the aforementioned monitors to mixed particle fields ranging from thermal energies to several giga-electron-volts was simulated. Because neutrons are the main contributor to total dose at many locations around the accelerators, dedicated neutron experiments were carried out at the Research Center for Nuclear Physics, Osaka University, utilizing quasi-monoenergetic beams of 250 and 392 MeV to benchmark the simulated detector responses. Good agreement was found at 392 MeV, whereas at 250 MeV the calculations predicted considerably higher readings of the detector than the ones observed experimentally.

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