Physicists have discovered two new isotopes

Scientists at the Institute of Modern Physics (IMP) under the Chinese Academy of Sciences (CAS), along with their collaborators, have developed two novel isotopes – osmium-160 and tungsten-156. This finding provides new insights into the structure of nucleosomes and suggests that lead-164 may have enhanced stability as a doubly nucleosome.

The study was published in Physical review letters and highlighted as an editors' recommendation.

The „magic numbers” of protons and neutrons make a nucleus particularly stable. Traditional magic numbers are 8, 20, 28, 50, 82 and 126. In previous studies, researchers found that traditional magic numbers were disappearing and new magic numbers were appearing in the nuclide table, rich in neutrons.

Do other traditional magic numbers disappear in highly neutron-deficient nuclear regions? Further study is of great importance to enrich and improve nuclear theories and to deepen our understanding of nuclear forces.

Experimental achievements and discoveries

In this study, the researchers conducted experiments at the Gas-Filled Recoil Separator-Spectrometer for Heavy Atoms and Nuclear Systems (SHANS) located at the Heavy Ion Research Center in Lanzhou, China.

Using a fusion evaporation reaction, researchers synthesized osmium-160 and tungsten-156 for the first time. They measured the α-particle energy and the half-life of osmium-160, an α-emitting isotope. Meanwhile, they determined that the daughter nucleus, tungsten-156, was a β⁺ emitter with a half-life of 291 ms.

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

Atomic Theory and Implications for Stability

„This trend is interpreted as evidence of a strengthening of the 82-neutron shell closure towards the proton trip line, which is supported by the increase in neutron-shell gaps predicted in theoretical models,” said Dr. Yang Huabin from IMP. Author of the paper.

Also, the researchers suggested that the enhanced stability of the 82-neutron shell closure may be due to its increasing proximity to the doubly magic nucleus lead-164, a stable nucleus with 82 protons and 82 neutrons. Although lead-164 is predicted beyond the proton-trip line, the enhanced shell effect has the potential to convert it into a bound or semi-bound nucleus.

Reference: “Discovery of new isotopes ¹⁶⁰Oz and ¹⁵⁶W: Revealing Improved Stability of N=82 Shell Closure on the Neutron Deficient Side” by 15 February 2024, Physical review letters.
DOI: 10.1103/PhysRevLett.132.072502

The study was conducted in collaboration with the University of Chinese Academy of Sciences, Guangdong Laboratory of Advanced Energy Science and Technology, Shandong University, Sun Yat-sen University, Guangxi Normal University, Dongji University and Institute of Theoretical Physics of CAS.