Radioactivity (and ionizing radiation) is ubiquitous and no living organism can evade it. It comes from natural sources, something from the rock in the earth’s crust, and is detectable in the air and even in drinking water. Large amounts of radioactivity were released in the nuclear tests of the 1950s and 1960s or in serious reactor accidents such as Chernobyl in 1986. If you want to find out something about the age, the activity, the origin and the dangerousness of radioactive materials, the analysis of the atomic nuclei of the radioactive elements (isotopes) in the sample helps. However, many techniques have weaknesses and only provide part of the information required. A new procedure developed by researchers from the Universities of Hanover and Mainz now promises significant progress in fast isotope analysis.
With the previous methods, a complex chemical preparation of the samples to be examined is usually necessary. This sometimes creates undesirable connections that make analyzes more difficult. In addition, all the material is used up during the measurements, so that nothing is left for further investigations. Another weak point: If there are elements whose atomic nuclei have the same mass number, so-called isobars, they cannot be differentiated from one another. This means that important information is lost, for example about the place of origin or the operating status of a reactor during an accident.
With their method, the researchers working with Clemens Walther can that you present in the journal “Science Advances”, eliminate these shortcomings by combining several analysis techniques in one device: you can quickly determine which elements are contained in your sample and in which quantities. With the help of resonant laser spectroscopy, they are then able to identify the isotopes of each individual element in the sample and determine its frequency. And they manage to depict the sample they are currently examining and examine the surface structure and the chemical nature of the material point by point. In doing so, they can draw conclusions about the distribution of the elements and isotopes.
Silent witnesses to the Chernobyl accident
Another plus point is that only tiny amounts, around 10,000 atoms, are required for the measurements. The sample remains undamaged and can be reused for further analyzes, such as chemical investigations, in which, for example, weathering processes are simulated.
“In principle, we can determine almost all elements of the periodic table,” says project manager Clemens Walther from the Institute for Radioecology and Radiation Protection in Hanover. The researchers are mainly interested in the actinides uranium, plutonium, americium, curium, but also in fission products such as strontium, cesium and technetium – elements that are formed during nuclear fission in a reactor and released in the Chernobyl accident in 1986. Walther and his colleagues tested their method themselves on two micrometer-sized particles from a soil sample that came from the vicinity of the damaged reactor.
The process is so sensitive that the researchers were able to detect the isotope americium-242m in a particle, which is only found in extremely small quantities in fuel. “The isotope tells us which operating states the reactor in Chernobyl went through before the explosion,” says Walther. The signals of the isobaric isotopes plutonium-241 and americium-241 could also be resolved so that they appeared as separate lines in the mass spectra. According to Walther, this is of great interest, since plutonium-241 decays into Amercium-241 with a half-life of only 14 years. As an alpha emitter, the latter is extremely radio-toxic and will be the dominant radiating isotope around Chernobyl in a few years’ time.
“For the use of contaminated areas, it is important whether and how quickly and which isotopes are possibly released from the particles on site. We could make a contribution here. ”The researchers want to make their process faster. “We currently need one working day to extract a particle, bring it into the apparatus and look at a maximum of four elements,” says Walther.
It is too long. Your goal is ten or twelve items a day. A prerequisite for this is that the laser system for isotope analysis, which was developed by researchers led by Klaus Wendt from the University of Mainz, can be switched through quickly over the wavelength range from the infrared to the ultraviolet spectral range. So far the tuning range is limited. Larger changes in the wavelengths of the incident laser light require modifications to the laser system.
The method can also be used for non-radioactive samples, explains Walther. This makes it suitable for determining the origin of archaeological samples, food or environmental toxins.