Mertens_NAIRAS_Aircraft_LWS_ESWE_2012

Report
Aircraft Human Radiation
Exposure
Christopher J. Mertens
NASA Langley Research Center
Hampton, VA.
Radiation Storms: Impact on Air
Travel
• Radiation Exposure to Commercial Aircrew and
Passengers
– The ICRP classify commercial aircrew as occupational radiation
workers
– The NCRP reported that flight crews receive the largest annual
effective dose among occupational radiation workers
– Current guidelines for maximum public and prenatal exposure
can be exceeded (1 mSv) on high-latitude commercial routes
during a single solar radiation storm event or for frequent flyer
exposure to high-latitude background levels (~ 10 flights/yr
during solar minimum)
• Increased Number of Commercial Polar Routes
– United Airlines flew 12 demo polar flights in 1999
– United Airlines flew 1832 polar flights in 2007
Radiation Storms: Impact on Air
Travel
• Summary of DOC (NOAA/SWPC) Report [2004]
– Typical cost savings from US-China cross-polar route ~ $35k-$45k per
flight compared to previous non-polar route
– However, rerouting polar flight can cost up to $100k per flight is fuel
stops and layovers are necessary
– FAA issued radiation advisory during Halloween 2003 storm and one
major airline rerouted six polar flights, which included fuel stops.
This cost the airline as much as $600k
• Other Reroutes
– United rerouted 26 polar flights during January 2005 storm period
and 5+ polar flights during the December 2006 storm period
– Delta Airlines rerouted 8 polar flights during January 2012 storm
period and 8+ polar flights during March 2012 storm period.
• The Emerging Commercial Space Transportation Industry and
Space Tourism
Nowcast of Atmospheric Ionizing
Radiation (NAIRAS) Model
• What Does NAIRAS Provide?
– Real-time effective dose rates from physics-based
models
– GCR and SEP sources
– 1x1 lat/lon geographic grid, 0-100 km with 1 km
vertical resolution, 1-hr time cadence
– Geomagnetic influences from solar-wind /
magnetosphere coupling
– Various graphical displays of effective dose rates and
representative high-latitude flight-accumulated
effective dose.
NASA’s NAIRAS Model Predictions During
March 2012 Solar Storm Events
Public Web site: http://sol.spacenvironment.net/~nairas/ (or google NAIRAS)
ESWE Workshop: An Aviation
Radiation Perspective
• What constitutes an extreme space weather event (Tuesday
morning session)?
– Any event that would require airlines to reroute flights in order to
avoid ICRP public/prenatal exposure limits from being
reached/exceeded
– What are the radiation effects on microelectronic systems for
commercial air/spaceflight?
• What recent space weather event(s) to include in “campaign”
analysis (Tuesday afternoon session)?
– January 20, 2005 SEP event: (1) “challenging” ion spectra, (2) high
anisotropy
– Neutron monitor site at Tibet (~ 14 GV) measured GLE of 2.4%,
indicating sufficiently large number of ~ 14 GeV protons!
– Peak incident SEP ion flux and subsequent atmospheric radiation
dose occurred in southern hemisphere in first few hours of the event
Backup Slides
Nowcast of Atmospheric Ionizing Radiation for Aviation Safety (NAIRAS) Model
NOAA/GOES +NASA/ACE Data
Cutoff Rigidity (IGRF)
Real-time Neutron
Monitor Data
(e.g., IZMIRAN and
LOMNICKY)
Fit to Climax HP
Spectral Fitting
Magnetospheric
Magnetic Field
(e.g., T05)
Effects on
Cutoff Rigidity
NASA/ACE Solar
Wind and IMF Data
Badhwar+O’Neill GCR Model
HZETRN
+
Dosimetry
Atmospheric Density
NCEP/GFS
Atmospheric Dose
and Dose Equivalent
Carrington Event
• SEP Spectral Fluence [Smart et al., 2006;
Townsend et al., 2006]
– Five measured spectral shapes considered
o August 1972 (soft)
o September 1989 (hard)
– Spectral shapes normalized to >30 MeV proton
fluence determined by impulsive NOy deposition
in polar ice cores [McCracken et al. 2001]
– Lack of detectable increase in annual 10Be
deposition in polar ice favors a soft spectrum
Carrington Event
• Geomagnetic Storm [Li et al., 2006]
– H-component depression measured in India and
taken as Dst
– Solar wind shock velocity: determined from time
between flare and magnetic disturbance
– Temerin and Li [2002] Dst model fits measured Hcomponent depression
o Interplanetary Ey = VxBz determine maximum Dst
depression
o Large solar wind density (to calculate dynamic pressure)
needed to reproduce rapid recovery
Carrington 1859
Carrington 1859
Carrington 1859
Carrington 1859
Carrington 1859
Aircraft Radiation Exposure
Medical Research
• Cosmic rays can directly break DNA strands in biological tissue, or
produce chemically active radicals in tissue that alter the cell
function [Wilson et al., 2005, 2003]
– Both can lead to cancer
• Other adverse health effects include, but are not limited to,
reproductive disorder and prenatal injury [Lauria et al., 2006;
Waters et al., 2000; Aspholm et al., 1999]
• Because aircrew total career dose is received is low doses per
flight, and accumulated slowly over the length of a flying career,
the direct evidence that a person can develop cancer as a result of
cosmic radiation is inconclusive
– Other lifestyle risk factors exist over a flying career
• However, radiation protection community accepts the Linear No
Threshold (LNT) theory
– Every radiation exposure will have an effect on human health
NIOSH Exposure
Assessment of
US Commercial Pilots
Poster 6/10 Soc Epi Res;
manuscript in review
FIRST STUDY OF
• US commercial pilot career exposure profile
from individual flight segments:
• Cosmic radiation
• Solar energetic particle events
• Chronic circadian disruption
FINDINGS
• A median pilot incurred
• 34.4 mSv GCR and flew through 6 SEPs
in 28 y flying
• 1.92 mSv in the last study year
• Exposure metrics increased markedly 1990+
IMPLICATIONS
• No dose limits for US crew
• Median pilot would trigger EU radiation
monitoring (>1mSv/y)
• A pregnant female pilot could exceed ICRP
guidelines for pregnant radiation workers
• High-exposed pilots at increased risk
Image courtesy of Kanzelhöhe Observatory
Aircraft Radiation Exposure
Recommendations and Actions
• Europe
– EU Directive 96/29/EURATOM (1996)
– Legal regulations on radiation protection of aircrew implemented into
national law with EU member states by 2000
– Exposures must be assessed if 1 mSv/yr is likely to be exceeded
– 6 mSv/yr “action level” (ALARA principle)
o Individual record keeping and medical surveillance required
– Monitoring recommended under 6 mSv/yr
– German implementation
o Operational GCR radiation exposure assessment using approved code
o No approved operational SEP radiation exposure assessment
o Some airlines interested in concomitant radiation measurements
• Japan
– State regulations recommend airlines try to keep aircrew exposure below 5
mSv/yr, which is the exposure dose limit for other occupationally exposed
workers in Japan
Aircraft Radiation Exposure
Recommendations and Actions
• USA
– ICRP recommendations (< 20 mSv/yr, < 1 mSv during pregnancy)
– Pregnant crewmember no more than 0.5 mSv in any month (FAA
recommendation)
• Current development of SpWx/aircraft radiation requirements
Radiation measurements/predictions
CPWG
SpWx User
Needs
ICAO
SpWx User
Requirements
WMO
Radiation assessment
FAA SpWx
AWG User
Needs
FAA
ICAO: International Civil Aviation Organization
NOAA/
SWPC
SEP Aircraft Radiation Exposure
High-Latitude Flights
• Roughly three SEP events per solar cycle with sufficient flux and
energy to significantly increase atmospheric radiation above GCR
• February 1956 Event (Wilson et al., 1995)
– Commercial: ~ 5 mSv
• October 1989 Event (AMS & SolarMetrics, 2007)
– Commercial: ~ 2 mSv
• Halloween 2003 Event (Mertens et al., 2010)
– Commercial (11 km, 10-hr): ~ 0.2 mSv
– Executive (15 km, 10-hr): ~ 0.4 mSv
• January 2005 Event (NAIRAS; Copeland et al., 2008)
– Commercial (11 km, 10-hr): ~ 1 mSv
– Executive (15 km, 10-hr): ~ 4 mSv

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