Potential benefit of retrospective use of neutron monitors in improving ionising radiation exposure assessment on international flights: issues raised by neutron passive dosimeter measurements and EPCARD simulations during sudden changes in solar activity.

Since air transport became more accessible, more and more people have been exposed to ionising radiation of cosmic origin. Measuring the neutron dose equivalent is a good approximation of total ambient dose equivalent, as neutrons carry about 50 % of the dose at flight altitudes. The aim of our study was to compare our measurements of the neutron component of secondary cosmic radiation dose, taken with passive dosimeters, with the data obtained from a simulation generated by EPCARD software, which is common in assessing flight crew exposure to ionising radiation. We observed deviations (both above and below) from the expected proportion of the neutron component (between 40 and 80 %), which pointed to certain issues with actual passive dosimeter measurement and the EPCARD simulation. The main limitation of the dosimeter are large uncertainties in high energy neutron response, which may result in underestimation of neutron dose equivalent. The main drawback of the software simulation is monthly averaging of solar potential in calculations, which can neglect sporadic high energy events. Since airlines worldwide almost exclusively use software (due to costs and convenience) to estimate the dose received by their crew, it is advisable to retrospectively recalculate the dose taking into account neutron monitor readings when solar activity changes.

Neutron radiation measurements on several international flights.

The earth is continually exposed to cosmic radiation of both solar and galactic origin. High-energy particles interact with the constituents in the atmosphere producing secondary particles that create radiation fields at aircraft altitudes. These secondary particles consist mainly of photons, protons, neutrons, charged and uncharged pions, and muons. The neutron component dominates the hadron cascade at lower altitudes as a result of its longer mean free path. Since air transportation has become more available to a greater number of people, this has led to an increase in the number of persons exposed to ionizing radiation of cosmic origin. This concerns pilots and cabin crews as well as frequent flyers. A neutron component of cosmic radiation was measured using an LR 115/CR-39 track detector associated with a 10B converter foil. The measurement of the neutron dose is a good approximation of the total dose since neutrons carry about 50% of the total ambient dose equivalent at aircraft altitudes. Also, the results of the measurements were compared with the data obtained by EPCARD software simulation. The measured neutron dose rate had a span from 0.36 to 8.83 µSv h(-1) (dose enhancement due to high solar activity in the flight period).

A neutron track etch detector for electron linear accelerators in radiotherapy.

BACKGROUND: Electron linear accelerators in medical radiotherapy have replaced cobalt and caesium sources of radiation. However, medical accelerators with photon energies over 10 MeV generate undesired fast neutron contamination in a therapeutic X-ray photon beam. Photons with energies above 10 MeV can interact with the atomic nucleus of a high-Z material, of which the target and the head of an accelerator consist, and lead to the neutron ejection. RESULTS AND CONCLUSIONS: Our neutron dosimeter, composed of the LR-115 track etch detector and boron foil BN-1 converter, was calibrated on thermal neutrons generated in the nuclear reactor of the Josef Stefan Institute (Slovenia), and applied to dosimetry of undesirable neutrons in photon radiotherapy by the linear accelerator 15 MV Siemens Mevatron. Having considered a high dependence of a cross-section between neutron and boron on neutron energy, and broad neutron spectrum in a photon beam, as well as outside the entrance door to maze of the Mevatron, we developed a method for determining the effective neutron detector response. A neutron dose rate in the photon beam was measured to be 1.96 Sv/h. Outside the Mevatron room the neutron dose rate was 0.62 µSv/h. PACS: 87.52. Ga; 87.53.St; 29.40.Wk.