Validation of Modelling the Radiation Exposure due to Solar by csgirla

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									     Validation of Modelling the Radiation Exposure due to Solar Particle
                         Events in Aircraft Altitudes
1
 Peter Beck, 2David T. Bartlett, 3Pawel Bilski, 4Clive Dyer, 5Erwin Flückiger, 6Nicolas Fuller, 6Pierre Lantos, 7Günther Reitz,
8
 Werner Rühm, 9Frantisek Spurny, 10Graeme Taylor, 11Francois Trompier, 12Frank Wissmann
1
  ARC Seibersdorf research (ARCS), Health Physics, Austria; 2Health Protection Agency (HPA), UK; 3Institute of Nuclear
Physics, Poland; 4QinetiQ, Space Division, UK; 5University of Berne, Switzerland; 6Paris-Meudon Observatoire, France;
7
  German Aerospace Center (DLR), Radiation Biology Department, Germany; 8GSF, Institute of Radiation Protection,
Germany; 9Czech Academy of Science, Nuclear Physics Institute (NPI), Czech Republic; 10National Physical Laboratory
(NPL), UK; 11Institute de Radioprotection et de Sûreté Nucléaire (IRSN), France; 12Physikalisch-Technische Bundesanstalt,
Braunschweig (PTB), Germany.
Dose assessment procedures for cosmic radiation exposure of aircraft crew have been introduced in most
European countries according the corresponding European directive and national regulations(1). However
the radiation exposure due to solar particle events is still a matter of scientific research(2). Here we
describe the outline and preliminary results of the European research project CONRAD, WP6, Subgroup-
B about the current status of available solar storm measurements and existing models for dose assessment
of solar particle events in flight altitudes.


Introduction
Aircraft crew are exposed to cosmic radiation of galactic and solar origin as well as secondary radiation
produced in the atmosphere, by its interaction with the aircraft structure and its contents. Following
recommendations of the International Commission on Radiological Protection (ICRP) in Publication 60(3), the
European Union (EU) introduced a revised Basic Safety Standards Directive which included exposure to natural
sources of ionizing radiation, including cosmic radiation, as occupational exposure. Several European research
projects have been focused on measurements on board aircraft and modelling of the radiation exposure in flight
altitudes with great success(2,4,5). Due to an initiative by EURADOS a working group has been established
(Working Group 5 on Aircraft Crew Dosimetry) to co-ordinate research, including collating and summarizing
the scientific results and practical consequences of measurements in radiation workplaces of aircraft crew at
flight altitudes. Initiated partly by the same group of scientists an ISO standard was proposed. Part 1 of the
standard has been already finalized and is in the process of publication (6). Owing to the rare occurrence of events
giving rise to significant dose rates at aircraft altitudes, and to the fact of very rare measurements and data in the
past, sporadic increases of radiation exposure in flight altitudes due to solar events were not included in the
EURADOS working group report and the ISO standard on cosmic radiation exposure on aircraft crew. Again, by
an initiative of EURADOS a coordinative research project were started on modelling and validation of the
radiation exposure due to solar particle events. The project is part of the European research project CONRAD
(Coordinated Network for Radiation Dosimetry). Work package 6 is concerned with the co-ordination of
research in EU member states on the evaluation of complex mixed radiation fields at workplaces and is
organized in two task-groups. One task-group existing of 13 members from 12 different European research
institutes is working on aircraft crew radiation workplaces. The objective of this task-group is to coordinate
research activities in model improvements for radiation dose assessment due to solar particle events. The results
will aid European research, increase the efficiency of resource utilization, and facilitate the technology transfer
to practical application and support the development of standards. The work is mainly organized by means of
meetings to exchange information on research activities and co-ordinate progress. The co-ordination work will
be carried out in close co-operation with the task-group on complex fields at workplaces at high energy particle
accelerators and in the nuclear industry. There is a close liaison between both task-groups with joint meetings
and benchmark measurements. Results of the task-group on solar energetic particle events will be the validation
of models for dose assessment of solar particle events, using data from neutron ground level monitors, in-flight
measurement results obtained during a solar particle event and proton data measured by instruments onboard
satellite. The task-group will give a report on the validation study of improved methods for the characterization
and dosimetry of the exposure of aircraft crew from solar particle events. In the following an outline about
radiation exposure measurements to aircraft crew during during solar particle events as well as predictions based
on calculations are given.


Radiation measurements
Measurements of the radiation exposure on board aircraft from the galactic cosmic radiation component have
been done during the last decade quite extensively(2). Some of the research institutes installed radiation monitors
for long term investigations at aircraft(4,9). For those institutes it was possible to gather also data during sporadic

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solar particle events. For monitoring of radiation exposure due to solar events active radiation instruments were
used such as tissue equivalent proportional counter (TEPC), Geiger-Müller counter or Si-semiconductor
detectors or spectrometers. Radiation exposure measurements were performed during several solar particle
events(8,9,10). Figure 1 and Figure 2 show in-flight measurement results during GLE60 on 15 April 2001(8, 9). Both
measurements show a significant increase of the radiation exposure during the flight for a time period of up to
some 3 hours. The total increase in terms of the radiation quantity H*(10) was about 50% due to that ground
level event.

                                                   PRG-JFK 15/04/01 GLE 60 influence
                                   12                                                                      2,4



                                   10                                                                      2,0
                                                      D(Si)
  Altitude, km; Rates, µSv(Gy)/h




                                                      Altitude
                                                      E CARI6




                                                                                                                 Event rate; cm -2.s -1
                                   8                  H(MDU)                                               1,6
                                                      Event rate


                                   6                                                                       1,2



                                   4                                                                       0,8



                                   2                                                                       0,4


                                   0                                                                       0,0
                                   10:48   12:00     13:12         14:24       15:36   16:48   18:00   19:12
                                                                       Tim e, UTC




Figure 1: LIULIN measurements of GLE 60 during PRG-                                                                                           Figure 2: ACREM in-flight measurement of GLE 60 during
JFK flight(9).                                                                                                                                FRA-DFW flight and comparison with neutron monitor data
                                                                                                                                              from the ground station at Moscow(8).


Figure 3 shows the whole scenario of radiation exposure, the proton fluence rate measured by satellite, and the
ground level neutron monitor count rate during a solar storm which happened between October and November
2003 (Halloween storms)(10). The radiation monitor used which was fix-installed on-board a Lufthansa Airbus
A340, is a TEPC showing the low- and high-LET contribution separately. The ratio is significantly different
between GLE65 on 28 October 2003 and the following Forbush decrease. Figure 4 shows the relative deviation
of the radiation exposure in the radiation quantity H*(10) during the solar storm period compared with quiet
periods before and after the storm. While the variation of radiation exposure for the same flight routes is about
±10% in 12 km flight altitude, the deviation during the Halloween storm was about ±40% due to GLE65 and the
following Forbush decrease. On the other hand the Forbush decrease that started on the 29 October 2003 (see
Figure 3) has led to few days lasting rather important decrease of the exposure onboard aircraft. The
measurements performed with Liulin equipment onboard a Czech Airlines aircraft during the flight Sofia-Prague
just in the deep decrease showed that the exposure was about 28% lower when compared to normal solar activity
conditions(9).

                                                                                                                                                                                   GLE65

                                                                                                                                                                                              Solar storm




                                                                                                                                                                 Forbushdecrease



Figure 3: TEPC measurements during the Halloween storms                                                                                        Figure 4: Observation of about 40% increase and 30%
between October and November 2001. GLE65, GLE66 and                                                                                            decreases of the radiation exposure in 12 km due to GLE
GLE67 occurred during these time period(10).                                                                                                   65 and the following Forbush decrease(10).




                                                                                                                                          2
Solar event calculation
The radiation exposure due to solar particle events were estimated by some members of the task-group based on
models, neutron ground level monitor data, proton data measured by satellites, and using in-flight data measured
onboard aircraft during GLEs (e.g. SiGLE(11), QARM(13)). Several institutes of the task-group are working on
complex calculation methods based on SPE proton input spectra, atmospherics and magnetic models, and using
high energy transport Monte-Carlo codes (e.g. FLUKA, GEANT4, and MCNPX). Figure 5 show the radiation
exposure estimations for flights between Paris and New York with Concorde aircraft and between Paris and San
Francisco for sub-sonic flights during 31 GLEs (1994 to 2001)(14). Total doses up to some 5mSv per flight were
calculated. Most of the increasing radiation dose due to GLEs is in the order of some 100µSv per flight. Figure 6
shows a world dose map calculated for the radiation conditions during the recently occurred GLE69 on 20
January 2005 based on the SiGLE model(11). A Procedure to model in more detail possible anisotropies in the
GLE effects is currently being developed(12).




Figure 5: Worst case calculation for 31 GLEs for flights         Figure 6: World dose map calculated for the conditions
between Paris and New York with Concorde (1st and 2nd bar)       during GLE 69 on 20 January 2005 based on SiGLE model.
and Paris to San Francisco with subsonic aircraft (3rd and 4th
bar). GLE contribution (black bar), total dose (white bar).
The GLE numbers along horizontal axis are those of Table 1.
The GLEs taken into account are those significant in terms of
radiation dose.


Preliminary conclusions and further tasks
Calculated values of the radiation exposure due to GLEs range up to a total dose of some 5mSv per route on-
board supersonic flights and up to some 1mSv on board subsonic flights crossing the Polar region. The
occurrence of GLEs is on average one event per year giving a route dose a few tens of µSv, one event per decade
giving a route dose of a few hundred µSv, and perhaps one event per century giving a route dose a the order of
mSv. GLEs are most probable during the solar maximum, with an increased likelihood before and after the
maximum of sun’s activity of the eleven year solar cycle. Several in flight measurements have been performed
during GLEs. Calculations of radiation exposure due to ground level events are shown. The next step of the
EURADOS research consortium will be the performance of a validation study, comparing in-flight data and
calculations for selected historical ground level events. The dose data given in the radiation quantity H*(10) are
defined in terms of flight destination, flight route and cut off rigidity. Further, the comparison of different
models will be made for selected flight routes. The influence of the magnetic disturbances will be discussed as
well as the influence of different flight altitudes, and the worst case in terms of occurrence of the GLE at a
particular time.




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Acknowledgements
The CONRAD WP6 / SG-B members and contributors to the study would like to thank Aer Lingus, Air Canada,
Air Emirates, Air France, Air New Zealand, Alitalia, Austrian, Airlines, British Airways, Czech Airlines,
Finnair, Iberia, Icelandair, Lufthansa, NASA, Scandinavian Airlines System, VARIG, Virgin Atlantics for their
assistance of in-flight measurements. Further results of research part-funded by the European Commission,
Directorate-General Research, under the auspices of the European Commission RTD Programme: Nuclear
Energy (Euratom Framework Programme V, 1998-2002) Contract N° FIGM-CT-2000-00068, national research
funding, and research supported by Austrian Research Centers (Austria), Health Protection Agency (UK),
Institute of Nuclear Physics (Poland), QinetiQ, Space Department (UK), University of Berne, (Switzerland),
Paris-Meudon Observatoire (France), German Aerospace Center, Radiation Biology Department (Germany),
GSF, Institute of Radiation Protection (Germany), Czech Academy of Science, Nuclear Physics Institute (Czech
Republic), National Physical Laboratory (UK), Institute de Radioprotection et de Sûreté Nucléaire (France),
Physikalisch-Technische Bundesanstalt, Braunschweig (Germany).


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