In a landmark achievement for nuclear physics, a research team has for the first time experimentally proven a long-theorized decay pathway for an uncommon isotope of the element technetium. The discovery, made by scientists at the University of Cologne, confirms that technetium-98 can decay through a process known as electron capture, a finding that adds a crucial new detail to the comprehensive map of atomic nuclei and their behaviors. This observation resolves a decades-old question in nuclear science and provides a more complete picture of how elements transform.
The research provides the first concrete evidence that technetium-98, in addition to its primary decay mode, also transforms into molybdenum-98 by capturing one of its own inner-shell electrons. This process, where a proton in the nucleus combines with an electron to form a neutron, was suspected since the 1990s but had never been directly observed due to the extreme difficulty of isolating the isotope. The successful detection of this rare event refines the internationally recognized chart of nuclides, often called the nuclear periodic table, which is the authoritative resource on the properties and transformations of all known isotopes.
A Decades-Old Prediction Confirmed
The electron capture decay of technetium-98 (Tc-98) was first predicted by nuclear theorists decades ago, but its existence remained unverified until now. The process is a form of radioactive decay where an atom’s nucleus absorbs an electron from one of the innermost electron shells. This captured electron then merges with a proton within the nucleus, converting it into a neutron and releasing a neutrino. The result is that the element transmutes into a different one—in this case, from technetium (atomic number 43) to molybdenum (atomic number 44). While Tc-98 was known to decay primarily into ruthenium-98 through beta decay, the new findings show that electron capture occurs in approximately 0.3% of all decay events. This confirmation of a minor but significant decay branch provides a fuller understanding of the isotope’s properties.
The Experimental Challenge of Rarity
Observing this specific decay pathway was a formidable challenge due to the extreme scarcity of technetium-98. The isotope is not available in large quantities and must be isolated from more common isotopes. The University of Cologne research team overcame this hurdle by working with a sample of about three grams of technetium-99, a widely available isotope used in medical imaging. Within this sample, however, was a minuscule trace—only about 0.06 micrograms—of the sought-after technetium-98. The primary difficulty was detecting the faint signal of Tc-98’s electron capture amidst the overwhelming radiation produced by the far more abundant Tc-99.
Isolating a Faint Signal
Advanced Detection Setup
To succeed where previous efforts had not, the scientists designed a sophisticated experimental setup at the Institute of Nuclear Physics’ Clover measuring station. The core of their strategy involved suppressing the background radiation from the technetium-99. They developed a specialized lead shield that effectively blocked the unwanted signals, allowing the much weaker emissions from the technetium-98 decay to be clearly identified and measured. This meticulous approach was crucial for isolating the rare events.
A Patient Observation
Over a continuous measurement period of 17 days, the research team meticulously recorded data from their sample. Their patience and the precision of their instruments paid off, as they successfully registered approximately 40,000 distinct decay events that matched the signature of electron capture. This wealth of data provided unambiguous statistical proof that technetium-98 does indeed decay via this long-suspected channel. The results were published in the peer-reviewed journal Physical Review C.
Completing the Nuclear Chart
The outcome of this experiment has a direct impact on the chart of nuclides, the fundamental reference for nuclear scientists worldwide. This chart maps all known isotopes, their properties, and their modes of decay. The confirmation of Tc-98’s electron capture decay fills a previously empty space on this map. In future editions of the chart, the entry for technetium-98 will be updated with a red corner mark, a visual symbol indicating this newly verified decay pathway. This seemingly small addition represents a significant step toward completing our knowledge of nuclear behavior, piece by piece.
Implications for Nuclear Physics
Beyond simply confirming a theory, this discovery enhances the fundamental understanding of nuclear structure and stability. By precisely measuring the properties of rare decay processes, physicists can refine the complex models that describe the forces holding atomic nuclei together. Such precise evidence helps scientists better understand why certain combinations of protons and neutrons are stable while others are not. The techniques developed for this experiment also pave the way for future research into other rare and difficult-to-observe decay processes in neighboring nuclides. These studies collectively contribute to a more robust and predictive model of the atomic nucleus, with potential applications in fields ranging from astrophysics to nuclear medicine.