Aircrew Radiation Exposure Research Articles

A TLD-Microdosimeter for aerospace usage: Results relevant to airline pilots undertook long-haul intercontinental flights during March–May 2017

During high altitude long haul flights pilots, cabin crew and passengers are exposed to enhanced level of radiation originating from cosmic ray showers (CRS), produced via the interaction of very high-energy (~GeV) primary protons with the air molecules in Earth's atmosphere. The CRS are composed of energetic particles of diverse species, i.e. neutrons, protons, electrons, muons, pions and photons. Furthermore, the magnitude of aircrew radiation exposure depends on flight altitude and duration, geographical location (latitude), geomagnetic conditions and solar activity (modulation) status. In 1990 the International Commission on Radiological Protection (ICRP) classified airline crewmembers as “radiation workers”. A miniature passive microdosimeter (LiBe-14) based on LiF (TLD700) and Beryllium Oxide (BeO) thermoluminescence dosimeter chips emulating a large volume gas-filled Tissue Equivalent Proportional Counter (TEPC) was developed by one of the authors (BM). The LiBe-14 was deployed to assess the integrated ambient dose equivalent of two commercial pilots on long haul intercontinental flights during March–May 2017. The accumulated dose equivalents of 1st (38 y, Female, 148 total block hours) and 2nd (29 y, Male, 149 total block hours) pilots were evaluated to be 565 μSv ± 105 μSv and 738 μSv ± 137 μSv, respectively. The results agreed well within ±20% of simulated data evaluated using the well-known EPCARD (European Program Package for the Calculation of Aviation Route Doses) aviation dosimetry code. The implementation of LiBe-14 Microdosimeter in routine long haul, high-altitude commercial flights for the estimation of dose equivalent, average LET and quality factor relevant to impinging cosmic radiation is recommended.

Preface to measurement, specification and forecasting of the Solar Energetic Particle (SEP) environment and Ground Level Enhancements (GLEs)

The Sun emits energetic particles following eruptive events such as solar flares and Coronal Mass Ejections (CMEs). Solar Energetic Particles (SEPs) arrive in bursts known as Solar Particle Events (SPEs), which penetrate into the Earth’s magnetosphere. SEPs with large enough energy induce a complicated atmospheric cascade, which secondary particles lead to an enhancement of count rate of ground-based detectors e.g. Neutron Monitors (NMs). This class of SEPs is therefore referred as Ground Level Enhancements (GLEs). The characterisation of the high-energy SEPs environment with corresponding space weather effects is important for space flights, aviation, and satellite industry. In this topical issue recent developments, addressing important user needs in the space radiation environment domain are published. Some articles are relevant to the specification of the SEP environment whilst others focus on space weather prediction of SEP fluxes. Catalogues based on measurement and processing of SEPs including ground-based data, and modelling of aircrew radiation exposure during major events are also presented.

CONCORD: comparison of cosmic radiation detectors in the radiation field at aviation altitudes

Space weather can strongly affect the complex radiation field at aviation altitudes. The assessment of the corresponding radiation exposure of aircrew and passengers has been a challenging task as well as a legal obligation in the European Union for many years. The response of several radiation measuring instruments operated by different European research groups during joint measuring flights was investigated in the framework of the CONCORD (COmparisoN of COsmic Radiation Detectors) campaign in the radiation field at aviation altitudes. This cooperation offered the opportunity to measure under the same space weather conditions and contributed to an independent quality control among the participating groups. The CONCORD flight campaign was performed with the twin-jet research aircraft Dassault Falcon 20E operated by the flight facility Oberpfaffenhofen of the German Aerospace Center (Deutsches Zentrum fur Luft- und Raumfahrt, DLR). Dose rates were measured at four positions in the atmosphere in European airspace for about one hour at each position in order to obtain acceptable counting statistics. The analysis of the space weather situation during the measuring flights demonstrates that short-term solar activity did not affect the results which show a very good agreement between the readings of the instruments of the different institutes.

A NEW SEMI-EMPIRICAL AMBIENT TO EFFECTIVE DOSE CONVERSION MODEL FOR THE PREDICTIVE CODE FOR AIRCREW RADIATION EXPOSURE (PCAIRE).

The Predictive Code for Aircrew Radiation Exposure (PCAIRE) is a semi-empirical code that estimates both ambient dose equivalent, based on years of on-board measurements, and effective dose to aircrew. Currently, PCAIRE estimates effective dose by converting the ambient dose equivalent to effective dose (E/H) using a model that is based on radiation transport calculations and on the radiation weighting factors recommended in International Commission on Radiological Protection (ICRP) 60. In this study, a new semi-empirical E/H model is proposed to replace the existing transport calculation models. The new model is based on flight data measured using a tissue-equivalent proportional counter (TEPC). The measured flight TEPC data are separated into a low- and a high-lineal-energy spectrum using an amplitude-weighted 137Cs TEPC spectrum. The high-lineal-energy spectrum is determined by subtracting the low-lineal-energy spectrum from the measured flight TEPC spectrum. With knowledge of E/H for the low- and high-lineal-energy spectra, the total E/H is estimated for a given flight altitude and geographic location. The semi-empirical E/H model also uses new radiation weighting factors to align the model with the most recent ICRP 103 recommendations. The ICRP 103-based semi-empirical effective dose model predicts that there is a ∼30 % reduction in dose in comparison with the ICRP 60-based model. Furthermore, the ambient dose equivalent is now a more conservative dose estimate for jet aircraft altitudes in the range of 7-13 km (FL230-430). This new semi-empirical E/H model is validated against E/H predicted from a Monte Carlo N-Particle transport code simulation of cosmic ray propagation through the Earth's atmosphere. Its implementation allows PCAIRE to provide an accurate semi-empirical estimate of the effective dose.

A survey of the cosmic radiation exposure of Air Canada pilots during maximum galactic radiation conditions in 2009

Abstract With the cosmic radiation exposure at altitude in 2009 being at a relative high intensity due to the current position in the 11 year solar cycle, a year-long study of Air Canada pilots was undertaken. The empirical Predictive Code for Aircrew radiation exposure (PCAire) along with corresponding in-flight measurements were used to estimate their exposures from flight data and crew rosters continually provided by Air Canada. Almost all of the pilots studied received more than the annual general public limit of 1 mSv, with the majority receiving around 3 mSv and none exceeded the recommended intervention level of 6 mSv. The highest route exposures were found to be on flights from Canada to Asia, Europe and the Southern hemisphere. The routes with the highest dose rates were to Europe and the long haul flights over Canada and the northern USA, a result of the distortion of the vertical cutoff rigidity from the magnetic North Pole's location in Canada. Although altitude, geomagnetic latitude and flight time are contributing factors to the exposures to the pilots on each route, Canada's unique geomagnetic location indicated a need to assess Canadian aircrew over their careers.

Cosmic radiation exposure survey of an Air Force Transport Squadron

Abstract A combination of in-flight measurements and calculations from the predictive code for aircrew radiation exposure (PCAire) was used to assess the cosmic radiation conditions for a Transport Squadron in the Canadian Air Force. The equipment suite from the Royal Military College of Canada, including a TEPC and bubble detectors, were flown over a sampling of air routes while the survey of the Squadron members covered a 2½ year period over the recent solar minimum and, thus, maximum radiation conditions. Various comparisons were made between the measurements and calculations to confirm the results of this work. For this period, more than half received more than the general public limit of 1 mSv per year and most received 0.5 or 2.5 mSv, with some receiving almost 4 mSv. This wide variation reflected the varied nature of their deployments.

Development of a predictive code for aircrew radiation exposure

Using the empirical data measured by the Royal Military College with a tissue equivalent proportional counter, a model was derived to allow for the interpolation of the dose rate for any global position, altitude and date. Through integration of the dose-rate function over a great circle flight path or between various waypoints, a Predictive Code for Aircrew Radiation Exposure (PCAire) was further developed to provide an estimate of the total dose equivalent on any route worldwide at any period in the solar cycle.

Effect of “Noisy” sun conditions on aircrew radiation exposure

In computer codes used to estimate the aircrew radiation exposure from galactic cosmic radiation, a quiet sun model is usually assumed. A revised computer code (PCAIRE ver. 8.0f) is used to calculate the impact of noisy sun conditions on aircrew radiation exposure. The revised code incorporates the effect of solar storm activity, which can perturb the geomagnetic field lines, altering cutoff rigidities and hence the shielding capability of the Earth’s magnetic field. The effect of typical solar storm conditions on aircrew radiation exposure is shown to be minimal justifying the usual assumptions.

Dose calculations at high altitudes and in deep space with GEANT4 using BIC and JQMD models for nucleus–nucleus reactions

Radiation exposure of aircrew is more and more recognized as an occupational hazard. The ionizing environment at standard commercial aircraft flight altitudes consists mainly of secondary particles, of which the neutrons give a major contribution to the dose equivalent. Accurate estimations of neutron spectra in the atmosphere are therefore essential for correct calculations of aircrew doses. Energetic solar particle events (SPE) could also lead to significantly increased dose rates, especially at routes close to the North Pole, e.g. for flights between Europe and USA. It is also well known that the radiation environment encountered by personnel aboard low Earth orbit (LEO) spacecraft or aboard a spacecraft traveling outside the Earth's protective magnetosphere is much harsher compared with that within the atmosphere since the personnel are exposed to radiation from both galactic cosmic rays (GCR) and SPE. The relative contribution to the dose from GCR when traveling outside the Earth's magnetosphere, e.g. to the Moon or Mars, is even greater, and reliable and accurate particle and heavy ion transport codes are essential to calculate the radiation risks for both aircrew and personnel on spacecraft. We have therefore performed calculations of neutron distributions in the atmosphere, total dose equivalents, and quality factors at different depths in a water sphere in an imaginary spacecraft during solar minimum in a geosynchronous orbit. The calculations were performed with the GEANT4 Monte Carlo (MC) code using both the binary cascade (BIC) model, which is part of the standard GEANT4 package, and the JQMD model, which is used in the particle and heavy ion transport code PHITS GEANT4.

Monte-Carlo calculations of particle fluences and neutron effective dose rates in the atmosphere

Monitoring of radiation exposure of aircrew is a legal requirement for many airlines in the EU and a challenging task in dosimetry. Monte-Carlo simulations of cosmic particles in the atmosphere can contribute to the understanding of the corresponding radiation field. Calculations of secondary neutron fluences in the atmosphere produced by galactic cosmic rays together with the resulting neutron-effective dose rates are shown in this paper and compared with results from the AIR project. The PLANETOCOSMICS package based on GEANT4 and two models for the local interstellar spectra of galactic cosmic rays have been used for the calculations. Furthermore, secondary muon fluences have been computed and are compared with CAPRICE measurements.

Modelling of aircrew radiation exposure from galactic cosmic rays and solar particle events

Correlations have been developed for implementation into the semi-empirical Predictive Code for Aircrew Radiation Exposure (PCAIRE) to account for effects of extremum conditions of solar modulation and low altitude based on transport code calculations. An improved solar modulation model, as proposed by NASA, has been further adopted to interpolate between the bounding correlations for solar modulation. The conversion ratio of effective dose to ambient dose equivalent, as applied to the PCAIRE calculation (based on measurements) for the legal regulation of aircrew exposure, was re-evaluated in this work to take into consideration new ICRP-92 radiation-weighting factors and different possible irradiation geometries of the source cosmic-radiation field. A computational analysis with Monte Carlo N-Particle eXtended Code was further used to estimate additional aircrew exposure that may result from sporadic solar energetic particle events considering real-time monitoring by the Geosynchronous Operational Environmental Satellite. These predictions were compared with the ambient dose equivalent rates measured on-board an aircraft and to count rate data observed at various ground-level neutron monitors.

Characterisation of bubble detectors for aircrew and space radiation exposure

The Earth's atmosphere acts as a natural radiation shield which protects terrestrial dwellers from the radiation environment encountered in space. In general, the intensity of this radiation field increases with distance from the ground owing to a decrease in the amount of atmospheric shielding. Neutrons form an important component of the radiation field to which the aircrew and spacecrew are exposed. In light of this, the neutron-sensitive bubble detector may be ideal as a portable personal dosemeter at jet altitudes and in space. This paper describes the ground-based characterisation of the bubble detector and the application of the bubble detector for the measurement of aircrew and spacecrew radiation exposure.

Aircrew dosimetry using the predictive code for aircrew radiation exposure (PCAIRE)

During 2003, a portable instrument suite was used to conduct cosmic radiation measurements on 49 jet-altitude flights, which brings the total number of in-flight measurements by this research group to over 160 flights since 1999. From previous measurements, correlations have been developed to allow for the interpolation of the dose-equivalent rate for any global position, altitude and date. The result was a Predictive Code for Aircrew Radiation Exposure (PCAIRE), which has since been improved. This version of the PCAIRE has been validated against the integral route dose measurements made at commercial aircraft altitudes during the 49 flights. On most flights, the code gave predictions that agreed to the measured data (within +/- 25%), providing confidence in the use of PCAIRE to predict aircrew exposure to galactic cosmic radiation. An empirical correlation, based on ground-level neutron monitoring data, has also been developed for the estimation of aircrew exposure from solar energetic particle (SEP) events. This model has been used to determine the significance of SEP exposure on a theoretical jet altitude flight during GLE 42.

Space weather and commercial airlines

Space weather phenomena can effect many areas of commercial airline operations including avionics, communications and GPS navigation systems. Of particular importance at present is the recently introduced EU legislation requiring the monitoring of aircrew radiation exposure, including any variations at aircraft altitudes due to solar activity. With the introduction of new ultra-long-haul “over-the-pole” routes, “more-electric” aircraft in the future, and the increasing use of satellites in the operation, the need for a better understanding of the space weather impacts on future airline operations becomes all the more compelling. This paper will present the various space weather effects, some provisional results of an ongoing 3-year study to monitor cosmic radiation in aircraft, and conclude by summarising some of the identified key operational issues, which must be addressed, with the help of the science community, if the airlines want to benefit from the availability of space weather services.

Dose assessment of aircrew using passive detectors.

Radiation exposure of aircrew is a serious concern which has been given special emphasis in the European Council directive 96/29/Euratom. The cosmic ray induced neutron component can contribute more than 50% to the biologically relevant dose at aviation altitudes. Various computational approaches to route dose assessment, e.g. CARI, are in use nowadays and are compared with experimental data. Measurements of aircrew exposure usually involve extensive instrumentation in order to cover the whole particle spectrum and energy range present inside aircraft. Due to their small size and easy handling, thermoluminescence dosemeters represent an appropriate alternative. Previous measurements onboard aircraft applying the high-temperature ratio method with LiF:Mg,Ti dosemeters for the determination of an 'averaged' linear energy transfer of mixed radiation fields demonstrate the ability of this method to evaluate the dose equivalent, according to the Q(LETinfinity) relationship proposed by the ICRP. Measurements with CaF2:Tm dosemeters are currently in progress and are discussed here.

Global Measurements of the Radiation Exposure of Civil Air Crews from 1997 to 1999

The exposure of aircrew to the increased cosmic radiation at aviation flight altitudes will soon be treated in the European Union as an occupational risk, with the consequence that the radiation exposure of aircrew must be determined. This work describes about 200 h of in-flight measurements performed during a period of 22 months from 1997 to 1999 on cargo aircraft. Various monitors were used to measure different radiation field components and to investigate the spatial dose equivalent rate distribution and the spatial radiation field composition. The monitors were rem counters for neutrons, and a scintillator and an ionisation chamber for the directly ionising and photon components. One of the main goals was to calibrate the monitors in the cosmic radiation field at flight altitudes against a tissue-equivalent proportional counter (TEPC) used as a reference instrument for the quantity ambient dose equivalent. The sum of the readings of a neutron rem counter with its response extended to high energy neutrons and of an ionisation chamber was found to be a fair approximation of the total dose equivalent as measured by the TEPC. The 'field calibration factor' determined is 1.0 ± 0.1. The global dose equivalent distributions as a function of magnetic latitude and cut-off rigidity were obtained for the range of altitudes encountered in civil aviation and can be described by simple mathematical functions for use in rough dose-equivalent rate estimates. Surrounding the TEPC with an active shielding detector and the application of coincidence techniques allowed dose equivalent fractions of charged and uncharged particles in the cosmic radiation to be separated. The low-LET radiation component was found to consist of 90% charged particles and 10% photons while the high-LET component contains a fraction of 30% from protons (pions) and 70% from neutrons.

Radiation exposure monitoring in civil aircraft

Based on the 1990 Recommendation of the ICRP (ICRP Publication 60, Pergamon Press, Oxford, 1991) a European Directive [Official J. Eur. Communities 19 (1996) L159, 1–114] commits the European Union (EU) member states to revise their national radiation protection laws by the year 2000 such that the exposure of aircrews to the increased cosmic radiation prevailing at aviation flight altitudes will be treated as occupational risks. A consequence will be that employers must assess the aircrew exposure. The ACREM (Air Crew Radiation Exposure Monitoring) research project intends to investigate practically methods for aircraft dose equivalent determination. The in-flight measurements were carried out on cargo aircraft. Field calibrations were performed using Tissue-Equivalent Proportional Counters (TEPC) as the reference instrument. Various monitors were used to investigate the spatial doserate distribution. The measured data were collated according to the different altitudes and geomagnetic latitudes. The results obtained from various in-flight measurements are reported and a concept for a future routine dose assessment for aircrew is proposed.

Dosimetry Methods for the Measurements of the Radiation Exposure of Civil Air Crew

Civil air crew are exposed in the course of their work, to elevated levels of natural background radiation, namely secondary cosmic radiation of galactic and solar origin. Recent re-evaluations of the risk associated with radiation exposure in general and neutron radiation in particular; the trend towards higher cruising altitudes for sub-sonic aircraft; and proposals to include exposures in jet aircraft to natural sources of radiation as part of occupational exposure, have been factors in focusing attention on the radiation exposure of civil air crew. This paper considers the dosimetry methods available in order to assess the options for the monitoring and control of exposure.

Round Table Discussion - Radiation Exposure of Civil Aircrew

Round Table Discussion - Radiation Exposure of Civil Aircrew