IGFAE researchers are involved in a study that has discovered a unique resonance in beryllium-10, a radioactive isotope of this chemical element. The research, published in Physical Review Letters, has found this resonance at 7.27 MeV (megaelectronvolts), just below the energy threshold at which alpha particles could be released. This suggests that beryllium-10 excited at this energy has a strong alpha-cluster structure, behaving like two alpha particles and two neutrons bound together.
The experiment was carried out at the ReA6 accelerator, located at the Facility for Rare Isotope Beams (FRIB) at Michigan State University in the United States. Yassid Ayyad, Ramón y Cajal researcher and one of the main authors of the article, and Alicia Muñoz, PhD student, participated in the IGFAE. In this work, Yassid Ayyad performed the data analysis using a framework developed by IGFAE staff, including Alicia Muñoz. The tools used in this study will be important for future research on rare and exotic atomic nuclei, for clustering in nuclei.
Nuclear clustering
“Clustering is a universal phenomenon observed across various scales in nature. At the microscopic level, it manifests in the self-organization of bacteria or beads driven by chemical reactions. On the cosmic scale, it’s evident in the formation of galaxy clusters, which represent the largest gravitationally bound structures in the universe”, Yassid Ayyad explains.
This phenomenon extends to subatomic and nuclear realms as well, where the protons and neutrons of the atomic nucleus can rearrange to form helium or alpha clusters. The clustering phenomenon in nuclear physics can be attributed to the complex nature of the nucleus as a many-body, open quantum system
The archetypal example of clustering in atomic nuclei is often cited as the Hoyle state of carbon-12, a three-particle alpha resonance responsible to produce stellar carbon through the so-called triple alpha process, whereby three helium nuclei are transformed into one carbon nucleus.
In rare isotopes with an excess of neutrons, the clustering of the atomic nucleus can adopt exotic structures. This is the case for beryllium-10, composed of two alpha particles and two neutrons. The work published in Physical Review Letters uses beryllium-10 (10Be), a radioactive isotope that is mainly generated from the nuclear fission of oxygen or hydrogen nuclei in the atmosphere, which are hit by cosmic rays. To understand its properties, the scattering produced by the interaction between a particle beam (in this case, beryllium-10) and a target composed of pure deuterium gas has been studied.
In the experiment, the team found a resonance at 7.27 megaelectronvolts (MeV), just below the energy at which alpha particles could be released. This suggests that beryllium-10 excited at this energy exhibits a strong alpha-cluster structure, behaving like two alpha particles and two neutrons bound together. The findings were confirmed using a four-body model that simulates these interactions. This interaction can reveal important information about the structure and properties of materials at the atomic level.
The scattered deuterons were measured using the Active Target Time Projection Camera (AT-TPC), a gaseous detector, or active target, designed to study reactions involving rare isotope beams, which typically have very low intensities. The use of this instrument has been key to the finding, because although beryllium-10 has been studied extensively over the years, this resonance had not been discovered until now.
Key concepts:
Resonance: a nuclear resonant state represents a transient, metastable arrangement of protons and neutrons within an atomic nucleus, occurring at precise energy levels and exhibiting quantum mechanical properties like a short-lived, highly excited nuclear configuration.
Nuclear scattering: occurs when a particle beam (in the case of this work, beryllium-10) interacts with the atomic nuclei of another element (in this case, pure deuterium gas). This interaction can reveal important information about the structure and properties of materials at the atomic level.
Alpha particles: ionising radiation composed of two protons and two neutrons (like the nucleus of a helium atom). It is emitted during the process of alpha decay. These particles have a positive charge and a relatively large mass, so their penetrating power is very low (they are stopped by a sheet of paper, or human skin).
