Royal Military College of Canada

Health

Characterization of Radiation Fields and Dosimetric Implications at Jet Aircraft Altitudes

By: B.J. Lewis, L.G. I. Bennett, A.R. Green, M.J. McCall, P.D. Tume, J.R.M. Pierre, B. Ellaschuk and A. Butler, T. Cousins

The Royal Military College of Canada (RMC)/Defence Research Establishment Ottawa (DREO) group is actively involved in the characterization of radiation fields at aircraft altitudes from 6 to 24 km (20,000 to 80,000 feet). This work is in response to the recent recommendations of the International Commission on Radiological Protection (ICRP-60). The ICRP-60 has proposed a reduction in the annual stochastic dose limit for the general public and recognized the occupational exposure resulting from high-altitude operation of jet aircraft.

Canadian Forces Study: Canadian Forces Pilot Study (CFPS)

As a consequence of the ICRP-60 recommendations, the Canadian Department of National Defence sponsored the RMC/DREO group to perform a two-phase investigation to determine the total dose equivalent received by Canadian Forces (CF) pilots. Owing to the complexity of the radiation field, the measurement phase involved quantifying the dose equivalent from a variety of powered and passive radiation detection instrumentation which included: bare and lead-lined remmeters, BGO and NaI(Tl) gamma spectrometers, a tissue-equivalent proportional counter, a Bonner multi-sphere spectrometer, an ionization chamber, plastic scintillators, thermoluminescent dosimeters, neutron bubble detectors and an anthropomorphic phantom. In collaboration with the Environmental Measurements Laboratory (EML) of the US Department of Energy, this equipment suite was flown on a series of dedicated CF flights. The measurements indicated that the neutron component contributes about half of the total dose equivalent and supported the use of neutron-sensitive bubble detectors as the primary detection tool in the survey phase of the study.

In the survey phase, pilots measured their neutron dose equivalent using bubble detectors as part of their routine duties from which their occupational exposure was estimated. Only those pilots from the Transport Air Group received an exposure at the new Canadian public limit of 1 mSv y-1.

NASA Study: Atmospheric Ionizing Radiation (AIR) Study

As an extension of the collaborative work between RMC/DREO and the Environmental Measurements Laboratory of the US Department of Energy, the RMC/DREO research group participated in an international study with the National Aeronautics and Space Administration (NASA) Langley Research Centre (LRC) in the Atmospheric Ionizing Radiation (AIR) Study. This study investigated radiation exposure at high altitudes (20 km) in order to provide information on the possibility of future high-speed civil transport. This collaborative effort provided information on the ionizing radiation distribution, spectral distribution and corresponding intensities in the upper stratosphere using an instrumented ER-2 high-altitude aircraft based on a series of five flights on June 2-15, 1997. The Canadian instrumentation consisted of a tissue equivalent proportional counter, and a temperature-controlled instrument package of neutron bubble detectors. These results extend our previous work into the higher altitudes providing a more comprehensive database.

Aircrew Radiation Exposure at Commercial Jet Altitudes - Part I: Canadian Aircrew Radiation Environment Survey (CARES)

As a first step to assess commercial aircrew exposures in Canada, an extensive study was completed by the RMC/DREO group, the Air Transport Association of Canada and the Director General of Nuclear Safety. The Canadian Aircrew Radiation Environment Survey (CARES) consisted of a measurement phase and survey phase, involving a number of Canadian commercial air carriers (i.e., Air Canada, Canadian International, Canada 3000, First Air, Canadian Regional). In the measurement phase, a variety of radiation detection equipment consisting of a tissue equivalent proportional counter, an ionization chamber, a lead-modified remmeter, thermoluminescent dosimeters and neutron bubble detectors were flown on a round-trip First Air flight from Ottawa to Resolute Bay, and operated by RMC/DREO scientific personnel, in order to characterise the mixed-radiation field on a northern Canadian-based flight route. In the survey phase, 80 commercial aircrew used passive neutron bubble detectors during their normal flight duties to measure the route-specific dose over a one-year period. Using the results of the scientific flight in the measurement phase and additional computer code calculations with CARI 3C, the neutron dose measurements were scaled for all particle types yielding over 3100 measurements of the total dose equivalent on 385 different flight routes. This database now augments the previous one obtained during the Canadian Forces Pilot Study (CFPS). This extensive set of measurements was incorporated into a Database Management computer program, which reported all of the results and, in addition, provided a capability for route and individual dosimetery calculation and dose prediction.

Part II: Predictive Code for AIrcrew Radiation Exposure (PCAIRE)

Many countries around the world are now developing regulatory policy in light of the ICRP recommendations requiring some form of exposure monitoring of aircrew. For example, the revised European Union (EU) Basic Safety Standard Directive, published in May 1996 (BSS96), requires that radiation protection measures for aircraft crew be incorporated into the national legislation of EU member states before 13 May 2000. In the United States, the Federal Aviation Administration (FAA) has formally recognized that aircrew members are occupationally exposed to radiation and should be subject to the same radiation protection policies practised by all other federal agencies. In Canada, a Commercial and Business Aviation Advisory Circular was issued on April 5, 2001 by Transport Canada to recognize the occupational exposure of aircrew.

Further studies were carried out by the Royal Military College of Canada (RMC) in collaboration with Transport Canada and the Director General Nuclear Safety to measure the complete cosmic radiation field at commercial jet altitudes using a portable instrumentation suite including an updated tissue equivalent proportional counter (TEPC), an ionisation chamber, an extended range neutron detector, thermoluminescent detectors and neutron-sensitive bubble detectors. In this work, the ambient total dose equivalent rate was measured with the TEPC on 76 flight routes, resulting in over 25 000 data points at one-minute intervals at various altitudes and geomagnetic latitudes (i.e., which span the full cutoff rigidity of the Earth's magnetic field) during the solar cycle (i.e., for galactic maximum and minimum conditions). These data were also compared to similar experimental work at the Physikalisch Technische Bundesanstalt, using a different suite of equipment, to separately measure the low and high linear energy transfer components of the mixed radiation field, and to predictions with the LUIN and FLUKA transport code. Similar experimental results have since been obtained with the RMC portable instrumentation suite. All experimental and theoretical results were in excellent agreement. From these data, a semi-empirical model was developed to allow for the interpolation of the dose rate for any global position, altitude and date (i.e., solar modulation). Through integration of the dose-rate function over a great circle flight path, a Predictive Code for AIrcrew Radiation Exposure (PCAIRE) has been developed in Visual C++ to provide an estimate of the total dose equivalent on any route worldwide at any period in the solar cycle. The PCAIRE code is a much more capable and versatile predictor of aircrew radiation than the CARES database that was limited to only those routes measured in the CARES study.

Work In Progress

In progress are flights in conjunction with various aircrew organizations, commercial airlines and Canadian Forces Transport Air Group, and international laboratories to augment and extend our study to date. This work will be used to support policy decisions by Transport Canada and Director General Nuclear Safety for both commercial and Canadian Forces aircrew. PCAIRE is also being developed to interface with human resources databases and thus provide a capability for the management of aircrew occupational exposure.

Publications

  1. P.T. Tume, B.J. Lewis, L.G.I. Bennett, T. Cousins, T.A. Jones, B.E. Hoffarth, J.R. Brission, P. Goldhagen, A. Cavallo, W. Van Steveninck, M. Reginatto, P. Shebell, F. Hajnal, T.J. Jamieson and F.J. LeMay, "Assessment of the Cosmic Radiation Field at Jet Altitudes," Proceedings of the Radiation Protection and Shielding Topical Meeting, No. Falmouth, Massachusetts, April 21-25, 1996, p. 68-75. (Best Paper Award)
  2. P. Tume, L.G.I. Bennett, B.J. Lewis, T. Cousins, T.A. Jones, B.E. Hoffarth and J.R. Brisson, "Canadian Forces Pilot Survey: Technologically-Enhanced Exposure of Canadian Forces Pilots to Natural Background Radiation," RMC/DREO report RMC-CCE-NSE-97-1, July 1997.
  3. P. Tume, B.J. Lewis, L.G.I. Bennett, T. Cousins, B.E. Hoffarth, T.A. Jones and J.R. Brisson, "Canadian Aircrew Radiation Environment Study (CARES)," Proceedings of the Workshop on Cosmic Radiation, Electromagnetic Fields and Health Among Aircrews, Medical University of South Carolina, Charleston, South Carolina, February 5-7, 1998, p. 10-16. (invited paper)
  4. P. Tume, B.J. Lewis, L.G.I. Bennett, M. Pierre, T. Cousins, B.E. Hoffarth, T.A. Jones and J.R. Brisson, "Assessment of High-Altitude Cosmic Radiation Exposure Using Tissue Equivalent Proportional Counters and Bubble Detectors," Atmospheric Ionizing Radiation Investigators' Workshop, Langley Research Centre, Hampton, Virginia, March 30-31, 1998.
  5. P. Tume, B.J. Lewis, L.G.I. Bennett, M. Pierre, T. Cousins, B.E. Hoffarth, T.A. Jones and J.R. Brisson, "Assessment of Cosmic Radiation Exposure on Canadian-Based Routes," Proceedings of the 1998 Annual Meeting of the National Council on Radiation Protection and Measurements, Arlington, Virginia, April 1-2, 1998. (invited paper)
  6. P. Tume, L.G.I. Bennett, B.J. Lewis, H.K. Wieland, M.K. Reid and T. Cousins, "Development of a Portable Micro-Environmental Cell for the Testing of Neutron Bubble Detectors in a Simulated Jet-Aircraft Environment," Proc. 19th Annual Conference of the Canadian Nuclear Society, ISSN 0227-1907, Vol. 1, Session 3A, Toronto, Ontario, October 18-21, 1998.
  7. B.J. Lewis, P. Tume, L.G.I. Bennett, M. Pierre, T. Cousins, B.E. Hoffarth, T.A. Jones and J.R. Brisson, "Cosmic Radiation Exposure on Canadian-Based Commercial Airline Routes," Proc. 19th Annual Conference of the Canadian Nuclear Society, ISSN 0227-1907, Vol. 2, Session 5A, Toronto, Ontario, October 18-21, 1998.
  8. B.J. Lewis, P. Tume, L.G.I. Bennett, T. Cousins, B.E. Hoffarth, T.A. Jones and J.R. Brisson, "Review of Canadian Aircrew Route and Individual Dosimetry," 1998 Annual Meeting of the Aerospace Medical Association, Seattle, Washington, May 17-21, 1998. (invited talk)
  9. P. Tume, B.J. Lewis, L.G.I. Bennett, T. Cousins, T.A. Jones, B.E. Hoffarth and J.R. Brisson, "Canadian Aircrew Radiation Environment Study," Volume 1: Project Summary (p. 1-71), Volume 2: Database Report (p. A-1 to A-33), and Volume 3: Database Management System User's Guide (p. 1-31), RMC/DREO reports to Air Transport Association of Canada, RMC-CCE-NSE-98-1 V1, V2, V3, March 1998.
  10. P. Tume, B.J. Lewis, L.G.I. Bennett and T. Cousins, "Characterization of Neutron-Sensitive Bubble Detectors for Application in the Measurement of Jet Aircrew Exposure to Natural Background Radiation," Nuclear Instruments and Methods in Physics Research A, 406 (1998) 153-168.
  11. A.R. Green, B.J. Lewis, L.G.I. Bennett, M.R. Pierre and T. Cousins, "Commercial Aircrew Radiation Dosimetry Using a Tissue Equivalent Proportional Counter," 20th Annual Conference of the Canadian Nuclear Society, Montreal, Quebec, May 30-June 2, 1999.
  12. A.R. Green, M. McCall, B.J. Lewis, L.G.I. Bennett, "Investigation of Cosmic Radiation Exposure of Canadian Forces Aircrew," Project Report to Director General of Nuclear Safety, RMC-CCE-NSE-00-01 (v.1 and v.2), March 2000.
  13. A.R. Green, M. McCall, B.J. Lewis, L.G.I. Bennett, "Cosmic Radiation Exposure of Aircrew," Project Report to Transport Canada, RMC-CCE-NSE-00-02 (v.1 and v.2), March 2000.
  14. A.R. Green, M.J. McCall, B.J. Lewis, LG.I. Bennett and M. Pierre, "Cosmic Radiation Exposure of Canadian-Based Aircrew," Canadian Radiation Protection Association, ALARA 2000 Conference, Montreal, Quebec, May 29-31, 2000.
  15. B.J. Lewis, P. Tume, L.G.I. Bennett, M. Pierre, A.R. Green, T. Cousins, B.E. Hoffarth, T.A. Jones and J.R. Brisson, "Cosmic Radiation Exposure on Canadian-Based Commercial Airline Routes," Radiation Protection Dosimetry, Vol. 86, No. 1, (1999) 7-24 (and B.J. Lewis, L.G.I. Bennett and A.R. Green, Letter to the Editor, Radiation Protection Dosimetry Vol. 87, No. 4, (2000) 299-301).
  16. M.J. McCall, A.R. Green, B.J. Lewis, LG.I. Bennett, M. Pierre, U. Schrewe, K. O'Brien and E. Felsberger, "Canadian-Based Aircrew Exposure From Cosmic Radiation on Commercial Airline Routes," 21st Annual Conference of the Canadian Nuclear Society, ISBN 0-919784-66-6 (Session 2D), Toronto, Ontario, June 11-14, 2000.
  17. A.R. Green, M.J. McCall, B.J. Lewis, L.G.I. Bennett and M. Pierre, "Assessment of Aircrew Exposure from Cosmic Radiation on Commercial Airline Routes," to be presented at the Conference on Radiation Protection for Our National Priorities, Medicine, the Environment and the Legacy, American Nuclear Society, Radiation Protection and Shielding Division, Spokane, Washington, September 17-21, 2000.
  18. B.J. Lewis, M.J. McCall, A.R. Green and L.G.I. Bennett, "A Model for Prediction of Cosmic Radiation Exposure of Commercial Aircrew," American Nuclear Society Winter Meeting, Washington, DC, November 12-16, 2000 (invited).
  19. P. Tume, B.J. Lewis, L.G.I. Bennett, M. Pierre, T. Cousins, B.E. Hoffarth, T.A. Jones and J.R. Brisson, "Assessment of Cosmic Radiation Exposure on Canadian-Based Routes," Health Physics Vol. 79, No. 5, November 2000, p. 568.
  20. B.J. Lewis, L.G.I. Bennett, A.R. Green, M.J. McCall, M. Pierre and B. Ellaschuk, "Canadian Studies on Cosmic Radiation Exposure of Aircrew," 18th Annual International Aircraft Cabin Safety Symposium, Costa Mesa, California, February 11-15, 2001 (invited).
  21. B.J. Lewis, M.J. McCall, A.R. Green, L.G.I. Bennett, M. Pierre, U.J. Schrewe, K. O'Brien, E. Felsberger, "Aircrew Exposure from Cosmic Radiation on Commercial Airline Routes," Radiation Protection Dosimetry, Vol. 93, No. 4 (2001) 293-314.
  22. B.J. Lewis, L.G.I. Bennett, A.R. Green, M.J. McCall, B. Ellaschuk, A. Butler and M. Pierre, "Galactic and Solar Radiation Exposure to Aircrew During a Solar Cycle," submitted for publication.