C. Baixeras

SIMULTANEOUS MULTIWAVELENGTH OBSERVATIONS OF THE BLAZAR 1ES 1959+650 AT A LOW TeV FLUX

We present the resultsfroma multiwavelength campaignonthe TeVblazar1ES 1959+650, performed in2006May. Data from the optical, UV, soft- and hard-X-ray, and very high energy (VHE) gamma-ray (E > 100 GeV) bands were obtained with the Suzaku and Swift satellites, the MAGIC telescope, and other ground-based facilities. The source spectral energy distribution (SED), derived from Suzaku and MAGIC observations at the end of 2006 May, shows the usual double hump shape, with the synchrotron peak at a higher flux level than the Compton peak. With respect to historicalvalues,duringourcampaignthe sourceexhibiteda relatively highstateinX-raysand optical, while inthe VHEbanditwasatoneof thelowestlevelsofarrecorded.Wealsomonitoredthesourceforfluxspectralvariability onatimewindowof 10daysintheoptical-UVandX-raybandsand7daysintheVHEband.Thesourcevariesmorein the X-ray than in the optical band, with the 2Y10 keV X-ray flux varying by a factor of � 2. The synchrotron peak is locatedintheX-raybandandmovestohigherenergiesasthesourcegetsbrighter,withtheX-rayfluxesaboveitvarying more rapidly than the X-ray fluxes at lower energies. The variability behavior observed in the X-ray band cannot be

A novel approach for long-term determination of indoor 222Rn progeny equilibrium factor using nuclear track detectors

Abstract A detailed study of the measurement principles of airborne 222 Rn decay products by means of nuclear track detectors (NTDs), taking into account the range of variation of the parameters influencing their concentration indoors, has shown that it is not possible for the existing methods to obtain the associated long-term equilibrium factor with an appropriate accuracy. For this reason, we have established a novel approach based on the new concept of reduced equilibrium factor, which can be obtained from the only measurement of airborne 222 Rn and its α-emitter daughter ( 218 Po and 214 Po) concentrations using a passive, integrating and multi-component system of NTDs. We have found that the equilibrium factor has a linear dependence on the reduced equilibrium factor regardless the values taken for the rates of ventilation, of aerosol attachment and of surface deposition. By using well-controlled exposures in a reference laboratory, we have shown that the equilibrium factor values determined with our system agree with those obtained by active monitors. Finally, as a pilot test, several dosimeters were exposed in an inhabited Swedish single-family house. The results of this exposure suggest the usefulness of this method to perform routine surveys in private homes and in workplaces in order to estimate the annual effective dose received by the general public and the workers due to the presence of 222 Rn daughters.

The RAGENA dynamic model of radon generation, entry and accumulation indoors.

The complexity generated by the existence of a great number of parameters and processes affecting the generation of radon in the source, its transport in the source medium, its entry into a dwelling and its accumulation in the different rooms of a dwelling has led to the development of partial models and experimental studies that are focused on a given aspect. However, in order to model radon levels and dynamics in real houses, it is necessary to take into account all the parameters and processes affecting radon levels. This is the objective of the dynamic RAGENA model of radon generation, entry and accumulation indoors. The model has been adapted to a Mediterranean climate house under dynamic conditions, and the indoor radon and soil radon dynamics have been compared to experimental results. It has been found (i) that the model gives a soil radon dynamics similar to that obtained experimentally, (ii) a remarkable model-experiment agreement indoors and (iii) that the indoor radon dynamics is given by a permanent radon entry from building materials and a dynamic removal through ventilation, which is driven by indoor-outdoor temperature differences and wind speed.

Radon emanation from soil samples

Abstract The soil or bedrock beneath a building is one of the sources of radon gas in the indoor air. The 238 U content of samples of the soil or the bedrock can be measured by gamma ray spectrometry and is of interest because the uranium content in the soil is a precursor of the presence of the radon gas in the soil. The emanation of radon gas from different types of material can be estimated to some extent if the content of 238 U of a sample is known and the 226 Ra content is only minorly affected. The true emanation is, however, affected by various parameters. One of these parameters is the possibility or not for the gas to come out from the grains into the air in the space between the grains of the sample. In this study we report the results from measurements of radon gas emanating from samples of soil frequent in the Lund region in Sweden and in the Barcelona region in Spain. As soils have different grain size it is important to know the type of soil. The 238 U content of the soil is measured with gamma ray spectrometry. The radon measurements are made by Kodak plastic film in closed cans, filled with the soil according to a technique, developed for radon measurements in water samples. The result shows, that the combination of grain size and uranium content is important for the emanation of the radon gas from the grains of the soil.

Soil radon levels measured with SSNTD's and the soil radium content

Abstract The source of the radon gas 222 Rn in the ground air is the soil and the bedrock underneath. The potential radon level in the ground is given by the content of 226 Ra in the ground. The presence of 226 Ra is in turn dependent on the amount of 238 U in the ground, and these two isotopes are not always found to be in equilibrium in a sample of soil or bedrock. Especially if the soil is washed out, the radium content may be reduced. When the soil is the relevant source of the radon gas, it is interesting to look for a possible relation between the radon level and the radium content of the soil. In this paper we report on measurements of soil radon level carried out with SSNTDs at several European sites. Soil samples were collected at these sites and analysed with gamma spectrometry to determine their radium content. A comparison of the different degree of disequilibrium of radon, defined as the ratio between the actual and the secular equilibrium-with-radium soil radon concentration, found at the different sites and depths is presented. The influence on the result of soil type and climate is briefly discussed.

Experimental and theoretical study of radon levels and entry mechanisms in a mediterranean climate house

Abstract An experimental study has been carried out in an inhabited single-family house. Radon concentration in the different rooms of the house and in its garden soil has been measured with Nuclear Track Detectors. No high differences of radon concentration have been observed between the different rooms of the house, so that the proximity of the room level to the soil seems not to affect the radon concentration. The annual radon concentration obtained indoors and in the soil has been respectively 35 Bq m −3 and 24 kBq m −3 . Since radon generation in the source, entry into indoor air and accumulation indoors depend on several parameters, the effect of a specific parameter on indoor radon concentration is difficult to explain from the radon measurements only. The RAGENA (RAdon Generation, ENtry and Accumulation indoors) model has been adapted to the room in the basement of the house. The mean radon concentration values obtained with the model are compared to experimental results derived from measurements using Nuclear Track Detectors. The use of the model, together with the experimental study, has allowed characterising radon sources, levels and entry mechanisms in the house. The concrete walls have been found to be the most relevant radon source, while the contribution of the soil is negligible in this case. The indoor radon level is given by the balance of the permanent exhalation from concrete and the removal due to ventilation. The indoor radon levels are close to the average value for the Barcelona area which, in turn, is close to the world averaged value.

Radon, radon progeny and equilibrium factor determination using an LR115 detector

Abstract Sensitivity, of an open LR115 type II strippable detector for radon and its progeny determination, depends on the layer removed by etching and this is theoretically studied in this paper. Based on the results obtained by this study, three new approaches to the long term measurement of alpha emitting radon progeny in air are proposed. Track density on an open LR115 track detector grows with increasing removed layer (or with etching time). This growth is dependent on the equilibrium factor between radon and its short lived progeny. The first method, which determines the equilibrium factor, is based on this fact, and assumes multi step etching of the detector. The second method determines the concentration of 214 Po in air. The method is based on the different behaviour of 222 Rn, 218 Po and 214 Po partial sensitivities with increasing removed layer. The third method called the “obstacle” method enables the determination of 218 Po and 214 Po in air. This method requires an obstacle in front of an open LR115 detector. The partial sensitivities of 222 Rn, 218 Po and 214 Po in such obstacle exposure geometry, behave differently to allow their determination. A similar method can be developed for other SSNTD possessing an upper energy limit for alpha detection.

Radon levels in groundwaters and natural radioactivity in soils of the volcanic region of La Garrotxa, Spain.

Groundwater radon level and soil radionuclide concentration have been measured in the volcanic region of La Garrotxa (Catalonia, Spain) to further research on the origin and dynamics of high radon levels over volcanic materials found in this region. Water samples from different aquifers have been collected from wells and springs and the water radon levels obtained have been lower than 30 Bq l(-1). Soil samples have been collected from different geological formations (volcanic and non-volcanic), being Quaternary sedimentary deposits those that have presented the highest mean values of (40)K, (226)Ra and (232)Th concentrations (448 ± 70 Bq kg(-1), 35 ± 5 Bq kg(-1) and 38 ± 5 Bq kg(-1), respectively). Additionally, indoor/outdoor terrestrial radiation absorbed dose rate in air have been measured to better characterize the region from the radiological point of view. Terrestrial radiation absorbed dose rates measurement points have been chosen on the basis of geological and demographical considerations and the results obtained, from 27 to 91 nGy h(-1), show a clear relation with geological formation materials. The highest terrestrial gamma absorbed dose rate is observed over Quaternary sedimentary deposits as well. All these results help to better understand previous surveys related with indoor and outdoor radon levels and to reinforce the hypotheses of a radon transport through the fissure network.

Sensitivity determination and optimisation of a cylindrical diffusion chamber, for radon measurements, with a CR39 detector

Abstract This paper deals with the determination of the sensitivity of the CR39 detector for radon measurements. The sensitivity was calculated by applying the Monte Carlo method for a detector in a diffusion cylindrical chamber with different radii and heights. The sensitivity is reduced as the chamber dimension decreased. The uncertainty of radon concentration determination associated with the unknown radon progeny deposition on the inner chamber walls is discussed. This uncertainty can be almost completely avoided by using a chamber narrower than 1.25 cm and higher than 5 cm. Such design of the diffusion chamber can enable better and more accurate radon measurements to be achieved.

Analysis of sensitivity of LR 115 II in cylindrical diffusion chambers for radon concentration determination

In this paper an analysis of sensitivity of LR 115 II track etch detector for radon measurements in cylindrical diffusion chambers is performed using a Monte Carlo method. The response (sensitivity) of LR 115 II track detectors, placed at the bottom of the tube, depends on the tube height and radius. These dependences are studied for radon and its alpha emitting progeny. The total sensitivity decreases as the dimensions of the tube decrease. It is shown that in narrow chambers, with a radius less than 1.5 cm, sensitivity is not influenced by the fraction of deposited radon progeny on the walls. In chambers with a height smaller than 0.65 cm, only alpha particles emitted by 222Rn can be detected, so that radon determination is realizable without any influence of the radon progeny.