By Kayla Downs
Most people don’t think about physics in their daily lives a whole lot. Beyond perhaps what happens when we slam the brakes too hard while driving, or precariously balance our coffee on a ledge, we leave the ideas of physics to the scientists. And in the scientific community, the basic rules of physics are pretty well established. We call them the “laws” of physics for a good reason. One of these ideas is that lone neutrons are far too unstable to create a particle cluster of four neutrons and no protons. An atom is unstable (radioactive) when the particles that make up the nucleus, like neutrons, are unbalanced. The idea, then, that four unstable neutrons would be able to cluster together without a proton to stabilize them has been widely questioned in the physics community. This theoretical cluster that could exist is called a Tetraneutron.
In 1965, a paper by Cierjacks et al. concluded that there was no evidence of tetraneutrons, but further studies have since provided the possibility of their existence. In 2002, a french team of scientists tried observing the disintegration of beryllium and lithium nuclei by blasting beryllium-14 particles into carbon particles. By doing this, they were hoping to blow apart beryllium’s cluster of four neutrons (BEC 2016). They expected to observe four little flashes, but instead there was one larger flash, suggesting that the neutrons broke off as a cluster. What they knew about physics at the time caused them to question what they had observed. In 2004, the same team observed a similar phenomenon, suggesting a grouping of four neutrons, but no one else had been able to replicate their results, making a confirmation impossible (BEC 2016).
Then, in 2016, a team from the University of Tokyo Graduate School of Science produced something called Tetraneutron states, by firing a beam of helium nuclei (two protons and six neutrons) at liquid helium (two protons and two neutrons). Four neutrons went missing upon collision for 1 billionth of a trillionth of a second (1.0 x 10-21 seconds) before reappearing as decay (Grant 2016).
Now you may be asking, just because they disappeared, what makes us think they all stayed clumped together? The team measured something that convinced them of that as well. By measuring the energy given off from the particles in the reaction, they concluded that there wouldn’t have been enough energy to propel each of the missing neutrons away independently. This leaves the only explanation being that the four neutrons that went missing stayed grouped together as a tetraneutron (BEC 2016). When these results can be replicated by other scientists, we may have something never before considered in physics on our hands.
While we can leave the microscopic measuring and observing to the scientists, we can be fascinated to learn elements of physics still being learned on our very Earth. In 2020, we think humans know most things about the world around us, especially something as reliable as physics, but new discoveries and anomalies like this show us that we truly don’t know everything, and that there is always something new to learn everywhere you look.
BEC Crew (2016, February 10). Physicists Say They've Finally Confirmed The Existence of a 'Four Neutron-No Proton' Particle. Retrieved October 21, 2020, from https://www.sciencealert.com/physicists-say-they-ve-finally-confirmed-the-existence-of-a-four-neutron-no-proton-particle
Cierjacks, S., Markus, G., Michaelis, W., & Pönitz, W. (1965, January 25). Further Evidence for the Nonexistence of Particle-Stable Tetraneutrons. Retrieved October 31, 2020, from https://journals.aps.org/pr/abstract/10.1103/PhysRev.137.B345
Deltuva, A. (2018, May 17). Tetraneutron: Rigorous continuum calculation. Retrieved October 21, 2020, from https://www.sciencedirect.com/science/article/pii/S0370269318304052
Yershov, Y. (2007, September 18). The Tetraneutron. Retrieved October 21, 2020, from https://www.mssl.ucl.ac.uk/theory/events/20070918/vladimir_yershov.pdf