Synthesis of osmium-160 and tungsten-156 reveals insights into shell closure and stability in neutron-deficient nuclei

At the Institute of Modern Physics (IMP) of the Chinese Academy of Sciences (CAS), scientists and their collaborators have synthesized two novel isotopes—osmium-160 and tungsten-156—marking a significant advancement in our understanding of nuclear structures. This breakthrough, detailed in a publication in Physical Review Letters and recognized as an Editors' Suggestion, has unveiled intriguing insights, hinting at the potential doubly magic nature of lead-164 and its heightened stability.

The concept of “magic numbers” in denotes specific configurations of protons and neutrons that endow atomic with exceptional stability. Conventionally, these magic numbers include 8, 20, 28, 50, 82, and 126. However, recent investigations have challenged the permanence of these traditional magic numbers, particularly on the -rich side of the chart of nuclides, raising questions about their disappearance in the extremely neutron-deficient nuclear realm. This calls for further to refine nuclear theories and deepen our comprehension of nuclear forces.

The experimental endeavors were conducted at the gas-filled recoil separator, Spectrometer for Heavy Atoms and Nuclear Structure (SHANS), located at the Heavy Ion Research Facility in Lanzhou (HIRFL), China. Employing the fusion evaporation reaction, researchers successfully synthesized osmium-160 and tungsten-156 for the first time. They meticulously measured the α- and half-life of osmium-160, an α-emitting isotope, while also identifying tungsten-156 as a β+ emitter with a half-life of 291 milliseconds.

A notable revelation from the study emerged when researchers analyzed the α-decay data of osmium-160. They observed a striking trend: an inverse relationship between proton number and decay rate among nuclei with 84 neutrons but varying proton counts. This suggests a reinforcement of the 82-neutron shell closure towards the proton drip line, corroborated by the predicted increase in neutron-shell gaps according to theoretical models.

Dr. Yang Huabin from IMP, the lead author of the paper, elaborated on this trend, highlighting its implications for the stability of nuclei. Additionally, researchers proposed that the bolstered stability of the 82-neutron shell closure may stem from its proximity to the potentially doubly magic nucleus, lead-164, comprising 82 protons and 82 neutrons. Despite lead-164 being projected beyond the proton-drip line, the augmented shell effect holds promise for its attainment of a bound or quasi-bound state.

This groundbreaking research not only expands our knowledge of nuclear structures but also underscores the intricate interplay between theory and experimentation in unraveling the mysteries of the atomic realm.

Source: Chinese Academy of Sciences

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