According to the World Health Organization, radon is the first risk factor for developing lung cancer among non-smokers, and the second in smokers. We are talking about a radioactive gas from the decomposition of radium 226 and which is the largest source of exposure to natural radiation in humans . According to a cartography by the Nuclear Safety Council, the geology of places like Galicia or Extremadura, mainly granitic, means that greater amounts of radon are released in these areas.
Radon is a gas that is usually harmless to health , but the problem comes when it accumulates inside buildings, usually in basements and lower parts of old buildings or in poorly ventilated places. Currently, a European directive of 2014 establishes the radon concentration thresholds above which it is considered a risk to human health and it is advisable to act. In our country, in December 2019 a new basic quality requirement in buildings was incorporated into the Technical Building Code regarding protection against radon gas, which also transposed the European regulations on the matter.
Quickly detect gas build-up
In addition to incorporating the appropriate security measures in new constructions, it is necessary to carry out fast and reliable measurements inside buildings that allow us to detect peaks of radon accumulation in order to act accordingly and therefore protect human health. In our country, a team of researchers from the Barcelona Institute of Microelectronics (IMB-CNM-CSIC) has collaborated in the design and development of a prototype for detecting gas that monitors its levels automatically and remotely.
“The dosimeters currently on the market perform passive measurements: you have to leave them for a few hours in the room where you want to measure radon and then go back and analyze the data,” explains Salvador Hidalgo, principal investigator at the IMB-CNM-CSIC in the project. “In other circumstances this may be correct, but when we talk about conditions that can affect health it is necessary to be more proactive, have control of the environment almost in real time and also be able to make the appropriate corrections automatically if radon levels they are high ”. The new prototype is a portable detector, which is plugged into the current and which provides real and periodic measurement through the wireless network to which it is connected. If the radon concentration exceeds a certain threshold, the ventilation elements would automatically activate to return to levels acceptable for human health.
” Radon concentrations vary a lot throughout the day, ” explains Manuel Lozano, deputy director of the IMB-CNM-CSIC White Room. “Generally there is a lot accumulated at the end of the night, in the morning it drops sharply as it is the time when buildings are usually aired, and then continues to accumulate throughout the day. In addition, atmospheric pressure also determines the release of radon, which increases when the pressure drops ”.
Features of the new prototype
The team has developed a semiconductor sensor for the detection of radioactive elements generated during radon decay and a control system capable of providing gas concentration measurements with frequencies below half an hour. This is the main novelty . “What most commercial detectors do is average the radon concentration recorded in the preceding 24/48 hours,” says Dolores Cortina, a researcher at the Galician Institute of High Energy Physics (IGFAE) of the University of Santiago de Compostela. “For this, the implementation of an algorithm adapted to the high capacities of the sensor developed has been key, allowing to combine speed and reliability in the measurement”, he adds.
The engineering that has had to be developed to maximize gas detection has been, for the researchers, one of the main challenges of the detector, which contains inside a silicon sensor manufactured in the Integrated Micro and Nanofabrication Clean Room of the IMB CNM-CSIC. “The radon detectors that exist today mount the detector on the sensor, which is usually a silicon chip, and use the silicon chips that already exist on the market. We have done it the other way around: we have manufactured a custom chip , with the optimal geometry to increase the sensitivity in radon detection ”, explains Lozano.
“The biggest challenge has been integrating the silicon into the heart of the radon detector; the final characteristics of the system depend on its quality, stability and repeatability ”, indicates Hidalgo. “Modular structures consisting of ten silicon detectors have been manufactured, of which three have been used for this prototype, positioned in a novel way. This solution allows us to have a very flexible system, with a quick and easy adaptation depending on the application ”, he adds.
Now, and once the prototype is ready, it will be necessary to develop it at an industrial level. “We are in the search stage for trading companies with the technical capacity to manufacture and distribute it on a large scale,” explains Lozano. “It is a very complex phase, but an important one: currently all the chip-based radon detection devices on the market come from outside the European Union . The current global shortage of microprocessors has highlighted how dangerous external dependence on the supply of chips is, ”he concludes.
