Continuous measurement of secondary neutrons from cosmic radiation at mountain altitudes and close to the North Pole--a discussion in terms of H*(10).

ABSTRACT

Two Bonner sphere spectrometers (BSSs) have recently been installed to measure secondary neutrons from cosmic radiation continuously, one at the environmental research station 'Schneefernerhaus' at an altitude of 2650 m in Germany and the other at the Koldewey station close to the North Pole in Ny-Alesund, Spitsbergen. After unfolding, both systems provide neutron fluence energy distributions as a function of time. Based on these distributions and on fluence-to-dose conversion coefficients, mean ambient dose equivalent rate values of 75.0 +/- 2.9 nSv h(-1) and 8.7 +/- 0.6 nSv h(-1) were obtained for October 2008, respectively (quoted uncertainties represent standard deviations of 124 values obtained during the measurement period). Ambient dose equivalent rates measured by means of an extended rem counter at the Schneefernerhaus agree with those based on the BSS neutron energy distributions within 5 %. The ambient dose equivalent rate was also calculated based on simulated FLUKA neutron energy distributions in the atmosphere. Even without detailed modelling of the local environment, an agreement better than 30 % was obtained between the ambient dose equivalent rate based on the FLUKA distributions and those based on the BSS measurements at the Schneefernerhaus, for neutrons above about 20 MeV. This agreement is expected to be even better if the influence of the local environment on the measured neutron fluence energy distribution will be calculated.