Scientists from the Institute of Modern Physics (IMP) of the Chinese Academy of Sciences (CAS) together with colleagues created two new isotopes: osmium-160 and tungsten-156. This discovery provides new insight into the architecture of the atomic nucleus and suggests that lead-164 may have increased stability as a potential double magic nucleus. The study was published on: Physical Examination Letters and highlighted as a recommendation from the editors.

A “magic number” of protons and neutrons can make the atomic nucleus particularly stable. The traditional magic numbers are 8, 20, 28, 50, 82 and 126. In previous studies, researchers found that traditional magic numbers disappear and new magic numbers appear on the neutron-rich side of the nuclide diagram.

Will other traditional magic numbers disappear in nuclear regions where neutron shortages are extreme? It is of great importance to conduct further research in order to enrich and develop nuclear theories and deepen our understanding of nuclear forces.

Experimental successes and results

In this study, researchers conducted an experiment on the gas-filled Recoil Separator-Spectrometer (SHANS) for Heavy Atoms and Nuclear Structure at the Heavy Ion Research Center in Lanzhou, China.

Researchers have synthesized osmium-160 and tungsten-156 for the first time using the thermonuclear evaporation reaction. They measured the energy of α particles and the half-life of osmium-160, an α-emitting isotope. Meanwhile, they determined that the daughter nucleus, named tungsten-156, was β.⁺ Emitter with a half-life of 291 ms.

With the newly measured α-decay data, the researchers deduced the reduced α-decay width for osmium-160 and compared it to other nuclei with 84 neutrons but fewer protons. They discovered a surprising trend: The higher the number of protons, the lower the decay rate.

Nuclear theory and implications for stability

The first author of the article is Dr. from IMP. “This trend is interpreted as evidence of increasing closure of the 82-neutron shell towards the proton flux line, which is supported by the increase in neutron-shell gaps predicted in theoretical models,” said Yang Huabin. .

Additionally, the researchers suggested that the increased stability of the 82 neutron shell could be explained by its increased proximity to the double magic lead-164 nucleus, which would be a stable nucleus containing 82 protons and 82 neutrons. Although Pb-164 is predicted to follow the proton drop line, the enhanced shell effect has the potential to make it a bound or semi-bound nucleus.