James Vary has been waiting for nuclear physics experiments to confirm the reality of a “tetraneutron” that he and colleagues theorized, predicted, and first announced during a presentation in the summer of 2014, followed by research in the fall of 2016.
“Whenever we come up with a theory, we always have to say that we’re waiting for experimental confirmation,” said Vary, a professor of physics and astronomy at Iowa State University.
In the case of four neutrons bound together (very, very briefly) in a transient quantum state or resonance, for Vary and an international team of theorists, that day is now.
The just announced experimental discovery of a tetraneutron by an international group led by researchers from the Technical University of Darmstadt opens doors for new research and could lead to a better understanding of the composition of the universe. This new and exotic state of matter could also have properties useful in existing or emerging technologies.
Neutrons, as you probably remember from science class, are subatomic particles with no charge that combine with positively charged protons to form the nucleus of an atom. Individual neutrons are not stable and convert into protons after a few minutes. Also, combinations of double and triple neutrons do not form what physicists call a resonance, a state of matter that is temporarily stable before decaying.
Enter the tetraneutron. Using supercomputer power at Lawrence Berkeley National Laboratory in California, the theorists calculated that four neutrons could form a resonance state with a lifetime as short as 3×10-22 Seconds, less than a billionth of a billionth of a second. It’s hard to believe, but that’s long enough for physicists to study.
Theorists’ calculations say that the tetraneutron should have an energy of about 0.8 million electron volts (a common unit of measurement in high-energy and nuclear physics – visible light has energies of about 2 to 3 electron volts). The calculations also said the width from the plotted energy peak exhibited by a tetraneutron would be about 1.4 million electron volts. The theorists published subsequent studies that suggested the energy would likely range from 0.7 to 1.0 million electron volts, while the width would range from 1.1 to 1.7 million electron volts. This sensitivity arose by adopting various available candidates for the interaction between the neutrons.
A recent article in the magazine Nature reports that experiments at the Radioactive Isotope Beam Factory at the RIKEN Research Institute in Wako, Japan, revealed a tetraneutron energy and width of about 2.4 and 1.8 million electron volts, respectively. These are both larger than the theoretical results, but Vary said uncertainties in the current theoretical and experimental results could mask these differences.
“A tetraneutron has such a short lifetime that it’s quite a big shock to the nuclear physics world that its properties can be measured before it decays,” Vary said. “It’s a very exotic system.”
It’s actually “a whole new state of matter,” he said. “It’s short-lived, but it portends possibilities. What happens when you put two or three of these together? Could you get more stability?”
Attempts to find a tetraneutron began in 2002 when the structure was proposed in certain reactions involving one of the elements, a metal called beryllium. A team from RIKEN found evidence of a tetraneutron in experimental results published in 2016.
“The tetraneutron will be only the second chargeless element on the nuclear map, alongside the neutron,” Vary wrote in a project summary. This “provides a valuable new platform for theories of the strong interactions between neutrons.”
Meytal Duer from the Institute for Nuclear Physics at the Technical University of Darmstadt is the corresponding author of the Nature Paper titled “Observation of a Correlated Free Four-Neutron System” and announcing experimental confirmation of a tetraneutron. The results of the experiment are considered a five sigma statistical signal indicating a definitive discovery with a 1 in 3.5 million probability that the result is a statistical anomaly.
The theoretical prediction was published in October 28, 2016 Physical Verification Letters, entitled “Prediction for a Four Neutron Resonance”. Andrey Shirokov of the Skobeltsyn Institute of Nuclear Physics at Moscow State University in Russia, who was a visiting scholar at Iowa State, is the first author. Vary is one of the corresponding authors.
“Can we create a small neutron star on Earth?” Vary titled a summary of the tetraneutron project. A neutron star is what’s left when a massive star runs out of fuel and collapses into a superdense neutron structure. The tetraneutron is also a neutron structure, a Vary jokes that it is a “short-lived, very light neutron star”.
Vary’s personal reaction? “I had pretty much given up experimenting,” he said. “I hadn’t heard about it during the pandemic. That was a big shock. Oh my god, here we are, maybe we actually have something new.”
Physicists demonstrate the existence of a new subatomic structure
M. Duer et al, Observation of a correlated free four-neutron system, Nature (2022). DOI: 10.1038/s41586-022-04827-6
Provided by Iowa State University
Citation: Theoretical Calculations Predicted Now Confirmed Tetraneutron, an Exotic State of Matter (2022, June 22), retrieved June 23, 2022 from https://phys.org/news/2022-06-theoretical-now-confirmed-tetraneutron -exotic-state .html
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