Determination of radiation exposition dose of flying personnel

As early as 1990, the International Commission on Radiological Protection (ICRP) determined from estimates that the occupational group of pilots and other flying personnel is exposed to cosmic radiation exposure comparable or even higher than that of persons exposed to Artificial radiation in medicine and technology. Therefore, the same criteria for radiation protection should also apply to this occupational group.

The ICRP has derived recommendations on, among other things, annual dose limits, which were adopted in European law in 1996 and German law in August 2001. In the amendment to the Radiation Protection Ordinance, appropriate rules for an individual dose determination have been laid down for compliance with the limit values.

As an immediate consequence of the ICRP recommendations, a number of European institutes had launched research programs aimed at the theoretical and experimental assessment of natural beam exposure in aircraft. The Helmholtz Zentrum München, which had already carried out appropriate research work in the 1970s, participated in both approaches and finally, with the support of the EU Commission, together with scientists from the University of Siegen, the EPCARD program (European Program Package for the Calculation of Aviation Route Doses). With its help, it is possible to calculate the beam exposure from all components of the penetrating cosmic radiation on any flight routes and flight profiles. This program is now available to interested parties.

Comparison of flight time (extended curve, right scale) and effective dose (left scale) for flights from Munich or Frankfurt (*) to selected destinations on the shortest route, sorted according to the duration of the flight. The dose values were calculated with EPCARDv3.2 for January 2002 for the following conditions: climb and descent respectively 30 min, assumed airports 37000 ft (about 11 km).

The physical background is as follows: The highly energetic galactic primary radiation - predominantly protons - from the interstellar space penetrates into our solar system, meets the earth's atmosphere and releases an avalanche of secondary particles. Neutrons, pions, mesons, electrons, photons and protons are generated. Depending on the energy and charge, the particles interact more or less strongly with the molecules of the earth's atmosphere, lose energy and are ultimately absorbed in the earth's atmosphere or in the solid soil. In addition to this shielding effect by the earth's atmosphere, the primary radiation is still shielded by two other effects, namely through the sun and through the earth's magnetic field. The sun sends out a huge stream of matter, the so-called solar wind, which has a radius of about a hundred astronomical units, which the charged primary particles must overcome. The intensity of the solar wind varies according to the solar activity, which can be seen in the number of solar spots, with a cycle time of 11 or 22 years. On the other hand, the earth's magnetic field is almost constant. It is easiest to overcome the poles, as the particle orbits are approximately parallel to the field lines. At the geomagnetic equator, on the other hand, the particles must have at least an energy of more than 15 GeV (= 15 billion electronvolts) in order to penetrate the earth's atmosphere perpendicular to the field lines. Since the much more frequent particles of lower energy are deflected away from the earth, the beam position is considerably less at the equator than at the poles.

All these effects were calculated using a so-called Monte-Carlo (MC) computing program and the best NASA models for galactic radiation and solar modulation. The MC program FLUKA (developed in many years by INFN and CERN +), used to describe the particle interactions, performs all physical processes using data sets from experiments on high energy accelerators. The result was then used as a data base for EPCARD.

Why not simply use measurements in airplanes to carry out the dose determination required by the legislator? This often asked question can be answered as follows:

1. Measurements with various suitable devices have been held at different times, at different geographic locations and at different airports, so that a physical model is needed that is "as accurate as possible" between these measurements. In any case, the entire "world matrix" can not be covered with measuring flights at all locations and at all times.

2. The legislator requires the determination of the "effective dose". This is a quantity for the estimation of the radiation risk, which includes the physical as well as radiation biology and other information. This includes, for example, the fact that neutrons have a considerably higher biological effect than photons, and that the radiation sensitivities of individual organs differ greatly. The effective dose is thus not directly measurable, but must be calculated either completely or from measurements, which are a first approximation for the dose values. Also for the latter method one needs so-called particle spectra, ie the number of particles, which are in each one of the many energy intervals. This information can only be obtained from MC calculations in the relevant energy range for dosimetry. This range is, for example, approximately between 0.001 electronvolt and 500 megoelectronvolt for neutrons.

With the program set up here, on-line doses can be calculated for each desired destination. For airlines, a full version for dose determination is available in the daily routine.

+ INFN = National Laboratory of Nuclear Physics, Italy. CERN = European Laboratory for High Energy Physics, Geneva, Switzerland.