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The results obtained from more than 1000 indoor and outdoor in situ gamma spectrometry measurements in 41 towns (from all geographic subdivisions) of the Greek mainland (not islands) are presented. From the in situ gamma spectra the absorbed dose rate in air due to uranium series, thorium series, 40K and 137Cs are derived and discussed.

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We investigated the transport of heavy-ion-induced electrons in solids by both experiment and numerical simulation. We measured electron yields from the beam entrance and exit surfaces of thin carbon foils ͑dϷ3 g/cm 2 -50 mg/cm 2 ͒ bombarded with swift, highly charged Cu qϩ ͑qϭ25-28 and E P ϭ9.6 MeV/u͒ and Ni qϩ ͑qϭ26, 28 and E P ϭ74 MeV/u͒ ions. We obtained the transport lengths of high-energy ͑Eտ100 eV͒ electrons and diffusion lengths of slow electrons ͑EՇ100 eV͒ and deduced a mean energy of the ejected electrons ͑Ϸ1 keV at 10 MeV/u and Ϸ8 keV at 74 MeV/u͒. The high-energy electrons represent a fraction of 15-20 % of the total electron yields at 9.6 MeV/u, but up to 35% at 74 MeV/u. We show that backscattering of fast, forwardemitted electrons towards the beam entrance surface cannot be neglected in fast-ion-induced electron emission. The experimental results are used as a benchmark for the improvement of our numerical simulation of the primary stage of the ion-matter interaction.

The dose rate conversion factors D(CF) (absorbed dose rate in air per unit activity per unit of soil mass, nGy h(-1) per Bq kg(-1)) are calculated 1 m above ground for photon emitters of natural radionuclides uniformly distributed in the soil. Three Monte Carlo codes are used: 1) The MCNP code of Los Alamos; 2) The GEANT code of CERN; and 3) a Monte Carlo code developed in the Nuclear Technology Laboratory of the Aristotle University of Thessaloniki. The accuracy of the Monte Carlo results is tested by the comparison of the unscattered flux obtained by the three Monte Carlo codes with an independent straightforward calculation. All codes and particularly the MCNP calculate accurately the absorbed dose rate in air due to the unscattered radiation. For the total radiation (unscattered plus scattered) the D(CF) values calculated from the three codes are in very good agreement between them. The comparison between these results and the results deduced previously by other authors indicates a good agreement (less than 15% of difference) for photon energies above 1,500 keV. Antithetically, the agreement is not as good (difference of 20-30%) for the low energy photons.