Site-selection criteria for the Einstein Telescope.

The Einstein Telescope (ET) is a proposed next-generation, underground gravitational-wave detector to be based in Europe. It will provide about an order of magnitude sensitivity increase with respect to the currently operating detectors and, also extend the observation band targeting frequencies as low as 3 Hz. One of the first decisions that needs to be made is about the future ET site following an in-depth site characterization. Site evaluation and selection is a complicated process, which takes into account science, financial, political, and socio-economic criteria. In this paper, we provide an overview of the site-selection criteria for ET, provide a formalism to evaluate the direct impact of environmental noise on ET sensitivity, and outline the necessary elements of a site-characterization campaign.

Analysis of trends, periodicities, and correlations in the beryllium-7 time series in Northern Europe.

The activity concentrations of beryllium-7, a natural radiotracer that is considered as a tracer of the stratospheric-tropospheric exchange, shows a distinct behaviour in Northern Europe compared to the central and southern parts of the continent. In this study, we use the measurements collected at four sampling stations in Scandinavia (Ivalo, Umea, Kista, Risoe) between 2001 and 2010 and investigate their trends, periodicities and residuals with the aim to further understand the common features in the beryllium-7 data records in northern sampling sites. The beryllium-7 activity concentrations exhibit statistically significant positive trends that range from an average value of 1.50%/year to an average value of 2.96%/year. We detect a one-year periodicity in all the sites, and in the southernmost site, Risoe in Denmark, additional higher-frequency harmonics. In the residual time series, we find outliers that represent occurrences of extremely high beryllium-7 activity concentration. Cross-correlations of the beryllium-7 residuals across the four sites decrease with increasing distance; similarly, as indicated by local Hurst exponents the records exhibit long-range correlations that weaken towards the end of the investigated period. To investigate the causes of the detected trends, we also calculate correlations between beryllium-7 and factors related to its production, transport and removal from the atmosphere: in particular, cross-correlations of the beryllium-7 residuals with residuals in sunspot number, local temperature, atmospheric pressure and precipitation, as well as Arctic Oscillation index and North Atlantic Oscillation index. Most of the obtained correlations, however, are not statistically significant, highlighting the need to analyse a longer time period in order to evaluate the impact of different factors on the airborne beryllium-7 activity concentration.

Xenon and radon time series analysis: A new methodological approach for characterising the local scale effects at CTBT radionuclide network.

A new methodology of time series analysis has been tested on 133Xe and estimated 220Rn activity concentrations in order to characterise the site response of four different CTBT/IMS monitoring stations. Seasonal variability of 133Xe and 220Rn at these IMS stations and the role played by different meteorological parameters on such variability have been quantified. As xenon and radon are both noble gases with similar physical characteristics but very different source terms, the methodology adopted in this comparative study, once coupled to analysis of radioxenon emission time series sampled at nearby NPPs or IPFs and to direct measurements of 220Rn at IMS sites location, might help assess relative influence of near and far field air on IMS radioxenon detections. Possible applications of the adopted methodology to radioxenon categorisation schemes are also discussed.

Uranium time series analysis: A new methodological approach for event screening categorisation.

Uranium (U) groundwater anomalies, detected before the L'Aquila earthquake (April 6th, 2009), represent a key geochemical signal of a progressive increase of deep fluids fluxes at middle-lower crustal levels associated with the geodynamics of the earthquake. Although the analyses performed in association with the seismic pattern around Gran Sasso National Laboratory and the geophysical and geochemical patterns of the Gran Sasso aquifer supported this hypothesis, a new approach for time series analysis has been developed for event screening categorisation and to highlight U as possible strain meter in geodynamical processes, particularly those which characterise active normal faulting.

Evaluation of 7Be and 133Xe atmospheric radioactivity time series measured at four CTBTO radionuclide stations.

Time series analysis of 7Be and 133Xe atmospheric data and meteorological parameters measured at four CTBTO/IMS radionuclide stations have shown great variability in terms of noise structures, harmonic content, cross-correlation patterns and local Hurst exponent behaviour. This study focused on highlighting and characterising both differences and similarities expected for these radionuclides due to their different physical and chemical characteristics along with their different source terms. Detrended crosscorrelation analysis of different meteorological parameters influencing the residuals time series has shown that for Canadian and American stations the parameters mostly affecting radionuclide concentrations in the air seem to be wind direction and atmospheric pressure.

Detection of radioxenon in Darwin, Australia following the Fukushima Dai-ichi nuclear power plant accident.

A series of (133)Xe detections in April 2011 made at the Comprehensive Nuclear-Test-Ban Treaty Organisation (CTBTO) International Monitoring System noble gas station in Darwin, Australia, were analysed to determine the most likely source location. Forward and backwards atmospheric transport modelling simulations using FLEXPART were conducted. It was shown that the most likely source location was the Fukushima Dai-ichi nuclear power plant accident. Other potential sources in the southern hemisphere were analysed, including the Australian Nuclear Science and Technology Organisation (ANSTO) radiopharmaceutical facility, but it was shown that sources originating from these locations were highly unlikely to be the source of the observed (133)Xe Darwin detections.

Estimation of the radioactive source dispersion from Fukushima nuclear power plant accident.

Following the Fukushima nuclear power plant accident detections of (133)Xe have been made in various locations. Using results of these remote measurements the Fukushima (133)Xe source term has been reconstructed and compared with previously reconstructed (137)Cs and (131)I source terms. The reconstruction is accomplished by applying atmospheric transport modeling and an adapted least square error method. The obtained results are in agreement with previous estimations of the Fukushima radionuclide source, and also serve as a proof of principle for source term reconstruction based on atmospheric transport modeling.

Ground gamma-ray survey of the Solforata gas discharge area, Alban Hills-Italy: a comparison between field and laboratory measurements.

Measurements of environmental radioactivity by HPGe gamma-spectrometry were carried out with the aim of investigating the distribution of natural radionuclides in a volcanic area and to compare two different methodologies - an in situ gamma-survey of the area and high accuracy laboratory measurements of soil samples. Results demonstrate good performance of the in situ technique, also confirmed by a correlation analysis between the results obtained by the two methodologies. A volcanic gas discharge area was chosen as the test site for the presence of natural long-lived radionuclides such as (40)K and (238)U, (235)U and (232)Th, and their decay chain members. Clear evidence of (222)Rn degassing in the area was confirmed by (226)Ra values measured by the in situ technique. Higher (40)K values measured by the in situ technique may be attributed to the presence of vegetation in the study area.

Estimation of the time-dependent radioactive source-term from the Fukushima nuclear power plant accident using atmospheric transport modelling.

Caesium-137 and Iodine-131 radionuclides released after the Fukushima Dai-ichi nuclear power plant accident in March 2011 were detected at monitoring stations throughout the world. Using the CTBT radionuclide data and the assumption that the Fukushima accident was the only source of these radionuclides, it was possible to estimate their time-dependent source-term fourteen days following the accident by using atmospheric transport modelling. A reasonable agreement was obtained between the modelling results and the estimated radionuclide release rates from the Fukushima accident.

Uranium groundwater anomalies and L'Aquila earthquake, 6th April 2009 (Italy).

Monitoring of chemical and physical groundwater parameters has been carried out worldwide in seismogenic areas with the aim to test possible correlations between their spatial and temporal variations and strain processes. Uranium (U) groundwater anomalies were observed during the preparation phases of the recent L'Aquila earthquake of 6th April 2009 in the cataclastic rocks near the overthrust fault crossing the deep underground Gran Sasso National Laboratory. The results suggest that U may be used as a potential strain indicator of geodynamic processes occurring before the seismic swarm and the main earthquake shock. Moreover, this justifies the different radon patterns before and after the main shock: the radon releases during and after the earthquake are much than more during the preparatory period because the process does not include only the microfracturing induced by stress-strain activation, but also radon increases accompanying groundwater U anomalies.

Ultra-low background measurements of decayed aerosol filters.

Aerosol samples collected on filter media were analyzed using HPGe detectors employing varying background-reduction techniques in order to experimentally evaluate the opportunity to apply ultra-low background measurement methods to samples collected, for instance, by the Comprehensive Test Ban Treaty International Monitoring System (IMS). In this way, realistic estimates of the impact of low-background methodology on the sensitivity obtained in systems such as the IMS were assessed. The current detectability requirement of stations in the IMS is 30 µBq/m3 of air for 140Ba, which would imply ~106 fissions per daily sample. Importantly, this is for a fresh aerosol filter. One week of decay reduces the intrinsic background from radon daughters in the sample allowing much higher sensitivity measurement of relevant isotopes, including 131I. An experiment was conducted in which decayed filter samples were measured at a variety of underground locations using Ultra-Low Background (ULB) gamma spectroscopy technology. The impacts of the decay and ULB are discussed.