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Radon concentrations indoors were determined in 24 typical occupied apartments in the city of Thessaloniki, North Greece (40 degrees 38'N, 22 degrees 58'E), by means of 12 surveys, each 2 mo long, over a 2-y period starting October 1989. The ratio of the winter and summer averages for the first year of measurements was 1.8 +/- 0.78, and for the second year of measurements was 1.6 +/- 0.61. The indoor radon concentration in the summer (1990) period ranged between 8 and 81 Bq m-3, while in the winter (1989-1990) it ranged between 20 and 143 Bq m-3 for the first year of measurements or between 8 and 92 Bq m-3 in the summer (1991) period and between 12 and 119 Bq m-3 in the winter (1990-1991) for the second year of measurements. These results were obtained by type CN-85 alpha track detectors. Some parameters that influenced the concentrations, such as precipitation rates and use of fly ash in building materials, are discussed.

Abstract. A network of three radon stations has been established in the Langadas Basin, northern Greece for radon monitoring by various techniques in earthquake prediction studies. Specially made devices with plastic tubes including Alpha Tracketch Detectors (ATD) were installed for registering alpha particles from radon and radon decay products exhaled from the ground, every 2 weeks, by using LR-115, type II, non-strippable Kodak films, starting from December 1996. Simultaneous measurements started using Lucas cells alpha spectrometer for instantaneous radon measurements in soil gas, before and after setting ATDs at the radon stations. Continuous monitoring of radon gas exhaling from the ground started from the middle of August 1999 by using silicon diode detectors, which simultaneously register meteorological parameters, such as rainfall, temperature and barometric pressure. The obtained data were studied together with the data of seismic events, such as the magnitude, ML, of earthquakes that occurred at the Langadas Basin during the period of measurements, as registered by the Laboratory of Geophysics, Aristotle University of Thessaloniki, in order to find out any association between them.

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Bremsstrahlung photon beam delivered by a linear electron accelerator has been used to experimentally determine the near threshold photonuclear cross section data of nuclides. For the first time, (γ,n) cross section data was obtained for the astrophysical important nucleus 162Er. Moreover, theoretical calculations have been applied using the TALYS 1.6 code. The effect of the gamma ray strength function on the cross section calculations has been studied. A satisfactorily reproduction of the available experimental data of photonuclear cross section at the energy region below 20 MeV could be achieved. The photon flux was monitored by measuring the photons yield from seven well known (γ, n) reactions from the threshold energy of each reaction up to the end-point energy of the photon beam used. An integrated cross-section 87 ± 14 mb is calculated for the photonuclear reaction 162Er(γ,n) at the energy 9.2 - 14 MeV. The effective cross section estimated using the TALYS code range between 89 and 96 mb depending on the γ-strength function used. The result for 162Er(γ,n), is found to be in good agreement with the theoretical values obtained by TALYS 1.6. So, the present indirect process could be a valuable tool to estimate the effective cross section of (γ,n) reaction for various isotopes using bremsstrahlung beams.