Physicists Synthesize New Isotopes of Osmium and Tungsten

A team of physicists in China has synthesized two new isotopes: osmium-160 and tungsten-156.

“Magic numbers of protons and neutrons can make an atomic nucleus particularly stable. The traditional magic numbers are 8, 20, 28, 50, 82 and 126,” said Dr. Huabin Yang, a physicist with the Institute of Modern Physics at the Chinese Academy of Sciences, and colleagues.

“In previous studies, physicists discovered the vanishing of traditional magic numbers and the emergence of new magic numbers on the neutron-rich side of the nuclide chart.”

“Will other traditional magic numbers disappear in extremely neutron-deficient nuclear regions?”

“Further exploration is of great significance to enrich and develop nuclear theories and to deepen our understanding of nuclear forces.”

In the new study, Dr. Yang’s team carried out the experiment at the gas-filled recoil separator-Spectrometer for Heavy Atoms and Nuclear Structure (SHANS) in Lanzhou, China.

Using the fusion evaporation reaction, the researchers synthesized two new isotopes: osmium-160 and tungsten-156.

They measured the α-particle energy and the half-life of osmium-160, which is an α-emitting isotope.

Meanwhile, they determined that the daughter nucleus, tungsten-156, is a β+ emitter with a half-life of 291 ms.

With the newly measured α-decay data, researchers derived the α-decay reduced width for osmium-160 and compared it with other nuclei with 84 neutrons but fewer protons.

They found a surprising trend: the higher the proton number, the lower the decay rate.

“This trend is interpreted as evidence for the strengthening of 82-neutron shell closure towards the proton drip line, which is supported by the increase of the neutron-shell gaps predicted in theoretical models,” Dr. Yang said.

“The enhanced stability of 82-neutron shell closure can be attributed to the increasing closeness to the doubly magic nucleus lead-164, which might be a stable nucleus with 82 protons and 82 neutrons.”

“Although lead-164 is predicted beyond the proton-drip line, the enhanced shell effect has the potential to make it a bound or quasi-bound nucleus.”

The study was published in the journal Physical Review Letters.

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H.B. Yang et al. 2024. Discovery of New Isotopes ¹⁶⁰Os and ¹⁵⁶W: Revealing Enhanced Stability of the N=82 Shell Closure on the Neutron-Deficient Side. Phys. Rev. Lett 132 (7): 072502; doi: 10.1103/PhysRevLett.132.072502