Most countries currently have radiological monitoring to monitor radioactivity levels in the environment and to detect the level of natural radioactivity. Also amongst its aims is to monitor the compliance with agreements such as the Comprehensive Nuclear Test Ban Treaty, as well as to detect and quantify a possible nuclear or radiological accident.
Depending on the frequency of the samples taken, these networks are classified into two groups: control networks, the aim of which is to measure radioactivity in the air, the water, the soil and in foods; and alert networks for informing of the anomalous presence of values in air and water.
To this end, alert networks take samples with frequencies of less than one hour and operate 24 hours a day. In Spain there exists a Radiological Alert Network and there are also four Autonomous Communities with their own networks, one of which the Basque Government launched in 2001.
Nevertheless, there has not existed to date a scientific methodology which enabled distinguishing between natural and anomalous values of radioactivity, to the point that certain radiological situations could go undetected. Ms Natalia Alegría Gutiérrez addressed this lacuna at the University of the Basque Country (UPV-EHU) with her PhD thesis, Drawing up alarm levels and analysis of transitory situations at radiological monitoring stations.
Dr. Alegría is an industrial engineer specialising in Energy Techniques and is currently working as lecturer-collaborator in the area of Fluid Mechanics at the Higher School of Engineering in Bilbao. Her PhD thesis was led by Dr. Fernando Legarda Ibáñez, of the Department of Nuclear Engineering and Fluid Mechanics and has been undertaken with the cooperation of the Nuclear Security Council (CSN).
The influence of precipitation
In order to detect a radiological incident, Dr. Alegría took the dose rate of gamma radiation, i.e. the amount of energy we receive per unit of mass over a specified unit of time. Her prime goal was to establish values for normal radiation situations, their origin being in natural sources of radiation: cosmic radiation from the Sun and interstellar spaces; and terrestrial radiation from radionucleids (originating in uranium or potassium, amongst others) present in the earth. Ms Alegría has chronologically ordered recorded dose rate values and shown that their evolution is constant (being represented on a horizontal line), although they do have an irregular component due to changes in meteorological values such as rainfall and lightning. That is, recorded values increase during periods of precipitation. The fact is that rainfall makes radioactivity present in the air fall to the earth’s surface (or to the rooftop where the probe or detector is located), and this causes the recorded dose rate to increase, without the cause being a radiological incident.
Effectively, the meteorological variables make it impossible for the evolution of radioactivity to be graphically represented using histograms. This is why Dr. Alegría decided to separate the behaviour of the dose rates over different periods, depending on the level of precipitation. Thus, she defined a dry period (0 litres per square metre), a wet period (whenever rainfall is greater than 0 litres per square metre) and a transition period, that encompasses the period from the end of the precipitations to the point where the gamma radiation dose rates return to those of the dry period.
Natural radioactivity and anomalous values
Taking as reference the magnitude that Currie called critical limit, Dr. Alegría calculated the critical limit of both the dry and rainy periods. In this way, every time the limits of the previous year are exceeded, a base alarm level is generated which will alert the experts to a possible radiological incident. To this end, she drew up a mathematical model in order to represent the increase undergone by the radioactivity during the rainy period with respect to the dry period.
Although the dose rate increases during the rainy period, it does not do so in a manner directly proportional to the amount of water fallen, but exponentially. According to Dr. Alegría, this is due to the rainfall transporting components derived from chains of radon (a radioactive gas) to the earth’s surface. In her PhD she also describes the systems of equations she used to distinguish between concentrations of radon due to natural causes and those caused by a radiological incident.
In conclusion, the PhD work presented by Ms Alegría at the UPV/EHU has made the radiological monitoring network in the Basque Country more sensitive, significantly reducing the number of alarms, but without there being radiological incidents that have gone undetected. The alarms of this network currently are triggered whenever there are external causes and not when a rise in natural radioactivity is caused by precipitations.
Alaitz Ochoa de Eribe | alfa
Did you know that the wrapping of Easter eggs benefits from specialty light sources?
13.04.2017 | Heraeus Noblelight GmbH
To e-, or not to e-, the question for the exotic 'Si-III' phase of silicon
05.04.2017 | Carnegie Institution for Science
More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.
Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...
Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.
"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...
The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.
Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...
The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...
Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.
Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...
28.04.2017 | Event News
20.04.2017 | Event News
18.04.2017 | Event News
28.04.2017 | Medical Engineering
28.04.2017 | Earth Sciences
28.04.2017 | Life Sciences