A Personal Use Program for Calculation of Aviation Route Doses

Transcription

1 A Personal Use Program for Calculation of Aviation Route Doses Hiroshi Yasuda a*, Tatsuhiko Sato b and Masato Terakado c a National Institute of Radiological Sciences, 9-1 Anagawa 4, Inage-ku, Chiba , Japan. b Japan Atomic Energy Agency, 4 Shirakatashirane 2, Tokai-mura, Naka-gun, Ibaraki , Japan c Visible Information Center, Inc.,440 Muramatsu, Tokai-mura, Naka-gun, Ibaraki , Japan Abstract. An Excel VBA program to calculate aviation route doses is developed for personal use by the general public. This program named as JISCARD EX runs on a personal computer installed with the Microsoft Excel 2003/2007. The JISCARD EX calculates instantaneously cut-off rigidities (Rc) and cosmic radiation dose rates at passing route points according to flight log data (latitude, longitude and altitude as a function of time). The Rc values for the Earth s magnetosphere are calculated with the MAGNETOCOSMICS code developed at the University of Bern. Solar activity represented as a force field potential (FFP) is evaluated from the observed trend of selected neutron monitors at high latitude. Future FFP values up to December 2008 are predicted from recently observed fluctuation of sunspot numbers. Cosmic radiation dose rates in the atmosphere are calculated using a PHITS-based analytical radiation model in the atmosphere (PARMA) developed in Japan. Calculated results are automatically summarized in a report of another Excel worksheet containing airport names, flying time, route dose and time plots of altitude, Rc and effective dose rate. This program will be open to the public through a web site of the National Institute of Radiological Sciences. KEYWORDS: JISCARD EX, cosmic radiation, aviation route dose, Excel, PARMA 1. Introduction Cosmic radiation intensities at aviation altitude (10~12km) are much higher than those on the ground and most of aircraft crew receive additional doses of more than 1mSv per year, i.e. the dose limit recommended for the general public. Accordingly, ICRP states that radiation exposure during the operation of jet aircraft should be considered as occupational exposure [1,2]. This recommendation has been followed most in Europe; the European Union (EU) has made a directive which orders member countries to perform assessments of cosmic radiation exposure for aircraft crew [3]. In Japan, the government has requested domestic airline companies to follow the guidelines made by the Radiation Council in 2006 [4] which states that annual aviation doses of aircraft crew are to be kept below 5mSv per year. The National Institute of Radiological Sciences (NIRS) has helped the airline companies to follow this guideline, particularly for calculation of aviation route doses. As a by-product of this work, a personal-use program for route dose calculation has been developed. 2. Program Description 2.1 Outline of the program This new program for route dose calculation, named as JISCARD EX, is written using the Excel VBA (Visual Basic for Applications) language and runs on the platform of Microsoft Excel 2003/2007. The dose rate at a point is calculated with a PHITS-based analytical model PARMA which was recently developed in Japan by Sato et al [5]. The flow of tasks for route dose calculation is shown in Fig.1. To use this program, just open an Excel file with a default name of JISCARD-EX-P.xls. On the first mainsheet as shown in Fig.2, you can * Presenting author, h_yasuda@nirs.go.jp 1

2 select one of three procedures according to flight route information available. With detailed log data, input or copy data to the mainsheet and push the Route Dose Calculation button (Fig. 2). Necessary flight data are time (h), latitude (north is positive), longitude (east is positive) and altitude (feet) as indicated on the mainsheet. A CSV-format data file can be uploaded from the Read Datafile or Look Sample button instead of direct input to the sheet. Figure 1: The task flow of route dose calculation using JISCARD EX. Main program (JISCARD-EX-P.xls) 3 Select a procedur 1 AIRPORT SEARCH (Original web program to get 2 Input flight log data and other parameters Determine departing and arriving airports. Is the route interpolation necessary? Yes Calculate a great circle route No Calculate a greatcircle route Set other parameter values Calculate a route dose using PARMA and output results Userfile (*.xls; report, route, condition, etc.) Figure 2: The initial main worksheet of JISCARD EX. 2

3 When detailed log data are unavailable, a user can obtain a representative route of a certain flight by choosing departing and arriving airports using an original program on the web. This program, named as AIRPORT SEARCH, incorporates Google Map (Fig.3) as a graphical interface for airport selection. In August 2008, a database of more than 1,000 airports has been uploaded. The corresponding great-circle route and flight time with a constant cruising altitude of 36,000 ft are automatically calculated and input on to the mainsheet. The resultant flight profile can be further modified by the user if necessary. Figure 3: The original web program to find and select departing and arriving airports. Soon after selecting the button of Route Dose Calculation on the mainsheet, calculation results including flight profile, route dose and trend graphs are automatically summarized in another worksheet as a report (Fig. 4). This sheet can be printed on an A4-size paper. Cut-off rigidities (Rc) at passing points are calculated with a GEANT4-base particle tracing code MAGNETOCOSMICS [6] developed by the cosmic ray group of the University of Bern. The newest version, which will be available until 2010, is employed here. The incident particle spectra of galactic cosmic rays (GCR) around the Earth are given from the local interstellar (LIS) spectra. Effects of solar modulation are evaluated with the Nymmik model [7] coupled with modified empirical parameters based on the force field formalism. According to the Rc values and GCR spectra that were independently estimated, cosmic radiation dose rates at passing points are calculated with the PHITS-based Analytical Radiation Model in the Atmosphere PARMA developed in Japan by Sato et al [5]. PARMA can calculate cosmic radiation doses in the atmosphere in a short time as precisely as the Monte Carlo simulation (PHITS code) can. Total effective dose and 1cm ambient dose equivalent are obtained as integrals of dose rates along the flight path. 3

4 Figure 4: The worksheet of calculation results summarized in a report style. Calculation results Date: 2008/9/1 Program: JISCARD EX Username: Jiscard Ex, Jr. 1. Date & Time 2008/8/30 19:40 2. Departure: THE WILLIAM B HARTSFIELD ATLANTA INTERNATIONAL (KATL/ATL), USA 3. Arriving: MINISTRO PISTARINI INTERNACIONAL (SAEZ/EZE), Argentina 4. Fying time: 9:43 Mileage: 5028 Miles 5. Solar potential: MV 6. Route dose: Effective dose E: 2.09E-02 msv Ambient dose eq. H*(1 2.51E-02 msv E rate H*(10) rate Dose rate (microsv / h) Time vs Dose rate from KATL_ATL to SAEZ_EZE 6.00E E E E E E E Time (hr) Altitude: Time vs Altitude from KATL_ATL to SAEZ_EZE 4.00E+04 Altitude (f t) 3.00E E E E Time (hr) Cut-off rigidity: 1.50E+01 Time vs Rc from KATL_ATL to SAEZ_EZE Rc (GV) 1.00E E E Time (hr) Route: 2.2 Comparison with Other Programs There are some programs for route dose calculation, such as CARI-6 [8], EPCARD [9], SIEVERT [10] and PCAIRE [11]. The characteristics of these models are well introduced in a report by the European dosimetry group [12]. In Fig.5, effective doses calculated with JISCARD EX are compared to those with CARI-6 for selected international flights. The estimations of JISCARD EX are 20~50% (30% in average) lower than those with CARI-6; no higher value was found. The main reason for this result is due to the recent revision of the radiation weighting factor (w R ) values [2]; the w R values for neutrons are considerably lower than those in the 1990 recommendations [1]. The effective doses obtained with JISCARD EX are lower than those with EPCARD [9] and SIEVERT [10] also (the results are not shown here). This difference is attributable mainly to employment of the new radiation transport model (PARMA) [5] which improved the accuracy for estimation of neutron energy spectra, particularly for neutrons with energies greater than 10MeV. A 4

5 software named EXPACS was developed on the basis of PARMA for calculating atmospheric cosmic-ray spectra [13]. Comparison with other programs are now in progress. Figure 5: Comparison of effective doses calculated with JISCARD EX and CARI-6 for thirty three round-trip international flights between major cities and Tokyo/Narita airport. It should be noted that 1cm ambient dose values (H*(10)) obtained with JISCARD EX are about 20% higher than effective doses. Thus, difference of H*(10) between JISCARD EX and other programs becomes smaller than that of effective dose. 3. Conclusion We have developed a new personal-use program JISCARD EX that enables an individual to know aviation route doses for any flight routes in a simple way. This new program can give effective dose values based on the 2007 ICRP recommendations [2]. It is hoped that this program will be a useful tool for educational purposes to facilitate understanding of natural radiation in the environment and also radiation exposure in aircraft. Comparison with other programs for route dose calculation [8-11] may be valuable in discussing the uncertainties which accompany to cosmic radiation dosimetry, i.e. nuclear reactions of high-energy particles up to GeV. The JISCARD EX program will be open to public from the web site of the National Institute of Radiological Sciences [14] soon after ongoing performance tests are completed. Acknowledgements The authors thank Mr. Susumu Ryufuku and Mr. Takumi Ajima, Visible Information Center, for technical cooperation. 5

6 REFERENCES [1] INTERNATIONAL COMMISSION ON RADIOLOGICAL PROTECTION, The 1990 Recommendations of the International Commission on Radiological Protection, Publication 60, Pergamon Press, Oxford (1991) [2] INTERNATIONAL COMMISSION ON RADIOLOGICAL PROTECTION, The 2007 Recommendations of the International Commission on Radiological Protection, Publication 103, Pergamon Press, Oxford (2007) [3] EUROPEAN UNION, Council Directive 96/29/EURATOM of 13 May 1996 laying down the basic safety standards for protection of the health of workers and the general public against the dangers arising from ionizing radiation. Off. J. Eur. Commun. L159 (1996) [4] MINISTRY OF EDUCATION, CULTURE, SPORTS, SCIENCE AND TECHNOLOGY, b_menu/shingi/housha/sonota/ htm (in Japanese) [5] SATO, T., YASUDA, H., NIITA, K., ENDO, A. AND SIHVER, L., "Development of PARMA: PHITS-based Analytical Radiation Model in the Atmosphere" Radiat. Res. 170, (2008) [6] COSMIC RAY GROUP, PHYSIKALISCHES INSTITUTE, UNIVERSITY OF BERN, [7] NYMMIK, R. A., PANASYUK, M. I., PERVAJA, T. I. AND SUSLOV, A. A., A model of galactic cosmic ray fluxes. Nucl. Tracks Radiat. Meas. 20, (1992). [8] FEDERAL AVIATION ADMINISTRATION: Radiobiology Research Team web page, 6/index.cfm [9] NATIONAL RESEARCH CENTER FOR ENVIRONMENT AND HEALTH: EPCARD, [10] SIEVERT web page: [11] PCAIRE Inc. : [12] EUROPEAN RADIATION DOSIMETRY GROUP: Cosmic radiation exposure of aircraft crew: compilation of measured and calculated data, A report of EURADOS Working Group 5. European Commission: Luxembourg (2004) [13] Excel-based Program for Calculating Atmospheric Cosmic-ray Spectrum (EXPACS): [14] Japanese Internet System for Calculation of Aviation Route Doses (JISCARD), ex/index_ex.html 6