REFLECT – Research flight of EURADOS and CRREAT: Intercomparison of various radiation dosimeters onboard aircraft

Aircraft crew are one of the groups of radiation workers which receive the highest annual exposure to ionizing radiation. Validation of computer codes used routinely for calculation of the exposure due to cosmic radiation and the observation of nonpredictable changes in the level of the exposure due to solar energetic particles, requires continuous measurements onboard aircraft. Appropriate calibration of suitable instruments is crucial, however, for the very complex atmospheric radiation field there is no single reference field covering all particles and energies involved. Further intercomparisons of measurements of different instruments under real flight conditions are therefore indispensable. In November 2017, the REFLECT (REsearch FLight of EURADOS and CRREAT) was carried out. With a payload comprising more than 20 different instruments, REFLECT represents the largest campaign of this type ever performed. The instruments flown included those already proven for routine dosimetry onboard aircraft such as the Liulin Si-diode spectrometer and tissue equivalent proportional counters, as well as newly developed detectors and instruments with the potential to be used for onboard aircraft measurements in the future. This flight enabled acquisition of dosimetric data under well-defined conditions onboard aircraft and comparison of new instruments with those routinely used. As expected, dosimeters routinely used for onboard aircraft dosimetry and for verification of calculated doses such as a tissue equivalent proportional counter or a silicon detector device like Liulin agreed reasonable with each other as well as with model calculations. Conventional neutron rem counters underestimated neutron ambient dose equivalent, while extended-range neutron rem counters provided results comparable to routinely used instruments. Although the responses of some instruments, not primarily intended for the use in a very complex mixed radiation field such as onboard aircraft, were as somehow expected to be different, the verification of their suitability was one of the objectives of the REFLECT. This campaign comprised a single short flight. For further testing of instruments, additional flights as well as comparison at appropriate reference fields are envisaged. The REFLECT provided valuable experience and feedback for validation of calculated aviation doses

Development of neutron detectors for use in radiation protection

The first part of this study consisted in testing performance of the several neutron detectors usually employed for radiation protec- tion at high-energy particle accelerators. The in- tercomparison was made at CERF, a unique workplace field that simulates the neutron spec- trum encountered in the proximity of high-en- ergy accelerators and at commercial flight alti- tudes. The CERF intercomparison campaign allowed to understand the behaviour of the different detector and quantify their over/underesti- mations with respect to the reference ambient dose equivalent function. Moreover, these experimental data were used to benchmark the new FLUKA simulation performed in 2017. The second part of this thesis was the investigation of a fast neutron detector for a novel radiation survey meter (called B-RAD) able to operate in the presence of a strong magnetic field, to be used for radiation surveys e.g. in the LHC experimental areas. The CLYC was selected as potential candidate for neutron detec-tion because of its promising properties, such as its capability to discriminate gamma rays from fast neutrons and its energy resolution. This thesis evaluated the performance of a 1- inch right CLYC cylinder coupled with a large SiPM array and compared the result with PMTs. The capacity of the CLYC+SiPm for spectros-copy was underligned. For neutron counting, new materials were investigated

Développement de détecteurs de neutron pour l’utilisation en radioprotection

The first part of this study consisted in testing performance of the several neutron detectors usually employed for radiation protec- tion at high-energy particle accelerators. The in- tercomparison was made at CERF, a unique workplace field that simulates the neutron spec- trum encountered in the proximity of high-en- ergy accelerators and at commercial flight alti- tudes. The CERF intercomparison campaign allowed to understand the behaviour of the different detector and quantify their over/underesti- mations with respect to the reference ambient dose equivalent function. Moreover, these experimental data were used to benchmark the new FLUKA simulation performed in 2017. The second part of this thesis was the investigation of a fast neutron detector for a novel radiation survey meter (called B-RAD) able to operate in the presence of a strong magnetic field, to be used for radiation surveys e.g. in the LHC experimental areas. The CLYC was selected as potential candidate for neutron detec-tion because of its promising properties, such as its capability to discriminate gamma rays from fast neutrons and its energy resolution. This thesis evaluated the performance of a 1- inch right CLYC cylinder coupled with a large SiPM array and compared the result with PMTs. The capacity of the CLYC+SiPm for spectros-copy was underligned. For neutron counting, new materials were investigated.La première partie de cette étude a consisté à tester les performances de plusieurs détecteurs de neutrons habituellement utilisés pour la radioprotection des accélérateurs de particules à haute énergie. La comparaison a été réalisée à la CERF, un champ unique qui simule le spectre neutronique rencontré à proximité d’accélérateurs à haute énergie et à des altitudes de vols commerciaux. La campagne a permis de comprendre le comportement des différents détecteurs et de quantifier leurs sur/sous- estimations par rapport à la fonction d'équivalent de dose ambiante de référence et de réaliser le benchmark des nouvelles simulations FLUKA réalisée en 2017. La deuxième partie de cette thèse portait sur l’exploration d’un détecteur à neutrons rapides destiné à un nouvel appareil de mesure capable de fonctionner en présence d’un champ magnétique puissant. Le CLYC a été choisi comme candidat potentiel pour la détection neutronique en raison de ses propriétés prometteuses, telles que sa capacité à discriminer les rayons gamma des neutrons rapides et sa résolution énergétique. Cette thèse évalue les performances d'un large cylindre CLYC couplé à une matrice SiPM et compare les résultats à ceux des PMT. Les capacités spectrométriques du CLYC ont été soulignées. Pour le comptage neutronique de nouveaux matériaux ont été étudié en perspective

Secondary neutrons inside a proton therapy facility: MCNPX simulations compared to measurements performed with a Bonner Sphere Spectrometer and neutron H*(10) monitors

Neutron spectrometry measurements with an extended-range Bonner Sphere Spectrometer (BSS), as well as neutron H*(10) measurements using an extended-range rem meter WENDI-2, a conventional rem meter LB 6411 and a tissue-equivalent proportional counter, were performed inside and around the Fixed-Beam Treatment Room at the proton therapy facility of Essen, in Germany. The WENDI-2 stood out as the easiest detector for making accurate neutron H*(10) measurements, since its direct measurements were equivalent to the H*(10) rates obtained with the BSS. The measurements were also compared to simulation results obtained with MCNPX 2.7.0 using two different selections of physics models for the hadron interactions above 150 MeV: the Bertini & Dresner models and the CEM03 model. For neutron H*(10) rates outside the treatment room, factors of 1.6–1.8 were obtained between the results of the two simulations, the Bertini & Dresner models yielding the largest values in all positions. The comparison of the simulation results with the WENDI-2 and BSS measurements for positions inside the treatment room showed that the Bertini & Dresner models reproduce the global neutron production in the water phantom relatively well, whereas the CEM03 model underestimates it by a factor of ∼1.3. At the most-forward angle, however, the Bertini model (unlike the CEM03 model) seemed to overestimate the production of neutrons with energies above 100 MeV. Outside the shielding, the simulated H*(10) overestimated the WENDI-2 measurements by factors of 2–3 with the Bertini & Dresner models, and 1.1–1.7 with the CEM03 model. Both simulations were thus conservative with respect to the neutron fluxes transmitted through the concrete walls. This conservative behaviour is probably caused by a combination of several uncertainties, including for instance uncertainties on the proton and neutron interaction cross-sections and uncertainties on the concrete composition and density.SCOPUS: ar.jinfo:eu-repo/semantics/publishe