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

Preliminary study of silica aerogel as a gas-equivalent material in ionization chambers

Since about two decades, a renewed interest on aerogels has risen. These peculiar materials show fairly unique properties. Thus, they are under investigation for both scientific and commercial purposes and new optimized production processes are studied. In this work, the possibility of using aerogel in the field of radiation detection is explored. The idea is to substitute the gas filling in a ionization chamber with the aerogel. The material possesses a density about 100 times greater than ambient pressure air. Where as the open-pore structure should allow the charge carriers to move freely. Small hydrophobic silica aerogel samples were studied. A custom ionization chamber, capable of working both with aerogel or in the classic gas set up, was built. The response of the chamber in current mode was investigated using an X-ray tube. The results obtained showed, under proper conditions, an enhancement of about 60 times of the current signal in the aerogel configuration with respect to the classic gas one. Moreover, some unusual behaviours were observed, i.e. time inertia of the signal and super-/sub-linear current response with respect to the dose rate. While testing high electric fields, aerogel configuration seemed to enhance the Townsend's effects. In order to represent the observed trends, a trappingâ\u80\u93detrapping model is proposed, which is capable to predict semi-empirically the steady state currents measured. The time evolution of the signal is semi-quantitatively represented by the same model. The coefficients estimated by the fits are in agreement with similar trapping problems in the literature. In particular, a direct comparison between the benchmark of the FET silica gates and aerogel case endorses the idea that the same type of phenomenon occurs in the studied case

Comparison between CLYC-6 and 3He for thermal neutron detection

A Cs$_2$LiYCl$_6$:Ce crystal, enriched in $^6$Li to > 95% (CLYC-6), was investigated for thermal neutron detection: it was characterised in terms of intrinsic efficiency and γ-ray discrimination capability and compared with a $^3$He counter (partial $^3$He pressure 2.3 atm). The intrinsic efficiency was determined by irradiating the detectors with thermal neutrons. The γ-ray discrimination capability was evaluated in a mixed neutron/$^{137}$Cs field. The intrinsic efficiency per unit volume is about a factor of 6.45 larger for CLYC-6 than for the $^3$He counter. The detectors’ performances in the presence of an intense γ-ray background are comparable: up to γ-ray fluence rates of the order of $10^5$ cm$^{-2}$·s$^{-1}$, both detectors correctly reject γ-rays. At fluence rates of the order of $10^6$ cm$^{-2}$·s$^{-1}$, CLYC-6 starts being affected by count losses due to γ-ray-induced dead time, while the $^3$He counter starts suffering from pile-up. Above this γ-ray intensity, both detectors are not reliable

A thermal neutron source for the CERN radiation Calibration Laboratory

International audienceThis work presents the design, construction and experimental characterisation of a lightweight and low-cost thermal neutron assembly, to be used with the existing Am–Be source irradiator of CERN radiation Calibration Laboratory (Cal Lab). The assembly consists of a cylindrical moderator (18 cm diameter, 25.5 cm height and 5.5 kg weight) and an optional reflector box (5 cm thick walls, 20 kg weight). The moderator is tailored to fit on the Am–Be source in its irradiation position, while the box encloses the detector under test during the irradiation. The exposure volume delimited by the box is 30 × 30 × 30 cm3. The thermal neutron fluence at the exposure location, i.e., 30 cm from the source, was optimized by FLUKA Monte Carlo (MC) simulations. The simulations were validated with measurements performed with a bare 3He proportional counter. The thermal neutron fluence at the nominal irradiation position is 7.43 × 102 cm−2s−1 with the cylindrical moderator only, and 5.75 × 103 cm−2s−1 with the cylinder and the reflector box, with the detector placed at the centre of the box. The thermal neutron fluence inside the box is rather uniform (variation <5%). •Design and construction of a new thermal neutron facility at CERN.•The facility consists of a compact, lightweight and low-cost polyethylene assembly.•The neutron field is produced by a source moderator and a thermal neutron reflector.•The design of the thermal neutron source is based on FLUKA Monte Carlo simulations.•Benchmarking of Monte Carlo simulations with experimental result

Impact of new operational dosimetric quantities on individual monitoring services

The new operational dosimetric quantities framework, proposed in the ICRU95 report, has stimulated the scientific community to start investigations that aim to assess its impact on radiation protection practices. As part of this effort, the present study describes an inter-comparison exercise among individual monitoring services (IMSs) on passive whole-body dosimetry. The inter-comparison is performed in terms of both the existing operational dose quantity Hp(10) and its proposed replacement Hp, to allow an evaluation of the actions that may be necessary to adapt dosimetry systems to the proposed quantity. For two of the tested IMSs, simple modifications to the detector response function, or the dose calculation algorithm, were sufficient to obtain results within acceptable limits. However, these approaches are not sufficient to give a level of performance comparable to that achieved in terms of Hp(10). This may require a modification to dosemeter design

Intercomparison of personal and ambient dosimeters in extremely high-dose-rate pulsed photon fields

International audienceRecent advances in laser driven accelerators boosted the development of high dose-rate fast pulsed systems all over the world. The stray radiation comprises primarily high-energy photons, resulting in extremely high dose rates within pico-/femto-second pulses. Dose measurements in such conditions have to be evaluated to validate methods. To tackle this challenge the EUropean RAdiation DOSimetry Group (EURADOS) started a program of dosimeters intercomparison, with a progressive approach, starting by a first evaluation in fields with μs pulse duration.The first comparison took place at the Lausanne University Hospital Center with an electron LINAC in Sept. 2017 involving 7 European institutes. Several passive and active dosimeters were tested with a tunable air kerma per pulse of the order of MGy/h. All instruments, except electrets, did not show any dose rate dependence, thus being selected as possible candidates for further studies