Experimental proposal Test of radiation protection instrumentation in HiRadMat

The knowledge of the response of radiation protection detectors in pulsed fields is very important, since this is a typical condition often encountered with stray radiation fields around particle accelerators at CERN and elsewhere. This document presents a proposal for testing a prototype detector and commercial instrumentation in use with the RAMSES monitoring system, due to the unique conditions that can be found in the HiRadMat facility. These tests can be extended to include instrumentation in use at other laboratories, both commercial devices and prototype units, and become an intercomparison benchmark exercise. Additional measurements include Bonner Sphere Spectrometry (BSS) measurements to verify experimentally the neutron spectra and ambient dose equivalent rates simulated by FLUKA inside HiRadMat.

Characterization of Extended Range Bonner Sphere Spctrometers in the CERF high-energy broad neutron field at CERN

Nikolaos Charitonidis, Angelo Esposito, Marco Silari

The accurate determination of the ambient dose equivalent in the mixed neutron-photon fields encountered around high-energy particle accelerators still represents a challenging task. The main complexity arises from the extreme variability of the neutron energy, which spans over ten orders of magnitude or more. Operational survey instruments, which response function attempts to mimic the fluence-to-ambient dose equivalent conversion coefficient up to GeV neutrons, are available on the market, but their response is not fully reliable over the entire energy range. Extended range rem counters (ERRC) do not require the exact knowledge of the energy distribution of the neutron field and the calibration can be done with a source spectrum. If the actual neutron field has an energy distribution different from the calibration spectrum, the measurement is affected by an added uncertainty related to the partial overlap of the fluence-to- ambient dose equivalent conversion curve and the response function. For this reason their operational use should always be preceded by an “in-field” calibration, i.e. a calibration made against a reference instrument exposed in the same field where the survey-meter will be employed. In practice the extended-range Bonner Sphere Spectrometer (ERBSS) is the only device which can serve as reference instrument in these fields, because of its wide energy range and the possibility to assess the neutron fluence and the ambient dose equivalent (H⁎(10)) values with the appropriate accuracy. Nevertheless, the experience gained by a number of experimental groups suggests that mandatory conditions for obtaining accurate results in workplaces are: (1) the use of a well-established response matrix, thus implying validation campaigns in reference monochromatic neutrons fields, (2) the expert and critical use of suitable unfolding codes, and (3) the performance test of the whole system (experimental set-up, elaboration and unfolding procedures) in a well controlled workplace field. The CERF (CERN-EU high-energy reference field) facility is a unique example of such a field, where a number of experimental campaigns and Monte Carlo simulations have been performed over the past years. With the aim of performing this kind of workplace performance test, four different ERBSS with different degrees of validation, operated by three groups (CERN, INFN-LNF and Politecnico of Milano), were exposed in two fixed positions at CERF. By using different unfolding codes (MAXED, GRAVEL, FRUIT and FRUIT SGM), the experimental data were analyzed to provide the neutron spectra and the related dosimetric quantities. The results allow assessing the overall performance of each ERBSS and of the unfolding codes, as well as comparing the performance of three ERRCs when used in a neutron field with energy distribution different from the calibration spectrum.

Elsevier2012

Radiation protection studies for CERN Linac4/SPL accelerator complex

Egidio Mauro

CERN is presently designing a new chain of accelerators to replace the present Proton Synchrotron (PS) complex: a 160 MeV room-temperature H- linac (Linac4) to replace the present 50 MeV proton linac injector, a 3.5 GeV Superconducting Proton Linac (SPL) to replace the 1.4 GeV PS booster (PSB) and a 50 GeV synchrotron (named PS2) to replace the 26 GeV PS. Linac4 has been funded and the civil engineering work started in October 2008, whilst the SPL is in an advanced stage of design. Beyond injecting into the future 50 GeV PS, the ultimate goal of the SPL is to generate a 4 MW beam for the production of intense neutrino beams. The radiation protection design is driven by the latter requirement. This thesis summarizes the radiation protection studies conducted for Linac4. FLUKA Monte Carlo simulations, complemented by analytical estimates, were performed 1) to evaluate the propagation of neutrons through the waveguide, ventilation and cable ducts placed along the accelerator, 2) to estimate the radiological impact of the accelerator in its low energy section, where the access area is located, and 3) to calculate the induced radioactivity in the air and in the components of the accelerator. The latter study is particularly important for maintenance interventions and final disposal of radioactive waste. Two possible layouts for the CCDTL section of the machine were considered in order to evaluate the feasibility, from the radiological standpoint, of replacing electromagnetic quadrupoles with permanent magnet quadrupoles with high content of cobalt. The present work provides complete information on beam loss assumptions, accelerator structure and duct and maze design, in order to make the present results of sufficiently general interest and provide guidelines for similar studies for intermediate energy proton accelerators. In addition to the Linac4-specific studies, this thesis also discusses FLUKA simulations performed to test the capability of the code, in a proton therapy application, in predicting induced radioactivity from intermediate energy protons. The thesis also reviews the analytical models mostly used for the calculation of neutron streaming through penetration traversing shielding barriers, discusses the FLUKA simulations performed to test the reliability of these models and, on the basis of the simulations, derives a universal expression that can be used to estimate the neutron transmission through a straight duct in direct view of the source, model missing so far in the literature.

EPFL2009

Order and Dynamics of Model Quantum Antiferromagnets

Martin Mourigal

The spin-1/2 Heisenberg antiferromagnets in one and two dimensions are important models in quantum magnetism in which many-body effects play a crucial role. Their collective excitations are associated with quasiparticles the interaction of which are difficult to describe. Neutron scattering offers a very powerful experimental technique to study these excitations. In addition, it can reveal the nature of exotic ground-states favored by competing frustrated interactions or by an applied magnetic field. This thesis presents neutron scattering studies of four materials, each representing a model magnetic system. • Cu(DCOO)2·4D2O (CFTD) is a model realization of the S =1/2 square-lattice antiferromagnet. It displays Néel order and its long-wavelength excitations are well described by renormalized spin-wave theory. In contrast, the excitations at the magnetic zone-boundary display anomalous dispersion and intensity close to (π, 0). A polarized neutron study of the anomaly additionally reveals the presence of a transverse continuum associated with a lineshape that extends to high energies. Results for the transverse and longitudinal continua are compared with Quantum Monte Carlo and fermionic Resonating Valence Bond theories. • (5CAP)2CuCl4 (CAPCC) is a S = 1/2 square-lattice antiferromagnet with modest saturation magnetic field Hs = 3.6 T and ∼ 20% antiferromagnetic interlayer coupling. Its spin excitations, measured above saturation are used to determine the microscopic exchange parameters of its Hamiltonian, while the presence of spontaneous magnon decay is investigated above the theoretically predicted threshold field H*= 0.76Hs. • CuSO4·5D2O is a model realization of the S = 1/2 antiferromagnetic Heisenberg chain. Its excitations are fully characterized in various regimes of applied magnetic field. In zero field, the presence of two- and four-spinon states is quantitatively confirmed, while the development of long-range Néel order is shown to preserve this picture qualitatively. In applied magnetic field, the excitations are studied with polarized neutrons and the existence of exotic psinons, anti-psinons and string-solutions continua is discussed. • LiCuVO4 is a S = 1/2 frustrated multiferroic chain material with competing ferromagnetic nearest and antiferromagnetic next-nearest neighbor interactions. Its magnetic structure is found to be a perfect circular cycloid the chirality of which can be tuned with an applied electric field. In crossed electric and magnetic fields, the behavior of the cycloid closely matches with that theoretically predicted from the spin supercurrent scenario. A magnetic-field induced transition to short-range longitudinal order is also evidenced with polarized neutrons. The present work was carried out in the Triple-Axis Spectrometers group at the Institut Laue Langevin in Grenoble, France and in the Laboratory for Quantum Mangetism at the EPFL, Switzerland.

EPFL2011