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The doubly magic nucleus of lead-208-it spins, though it shouldn’t

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To deploy an astronomical analogy, in as much as the majority of nuclei are similar in outline to rocky objects like moons or asteroids, then the nuclei of lead-208 under certain conditions resemble planets surrounded by a dense atmosphere that can move around a rigid core.

The situation here is more interesting, because the neutrons and protons form their own shells in the nuclei, which are particularly stable for numbers of nucleons that are known as magic numbers.

Physicists call nuclei with completely filled proton and neutron shells doubly magic. Lead-208 is unique in this group because it is the most massive doubly magic nucleus.

“In a high-spin state-the effect of a deep inelastic collision-the nucleus is excited and is trying to return to the lowest energy state. It gets rid of its excess in several to a few dozen stages, each one emitting gamma radiation with an energy characteristic for its transition. By analyzing the energies of this radiation, we are able to obtain a lot of information about the structure of atomic nuclei and the processes taking place within them,” explains Dr. Lukasz Iskra.

In normal states, the nucleus occurs for picoseconds, whereas in one of the isomeric states, the nucleus was detected for up to 60 nanoseconds-that is, a thousand times longer.

Researchers assume that at high spins, a rigid core is formed in the nucleus of lead-208; the next highest elemental mass is the doubly magic nucleus, i.e. tin-132.


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Post Author: R. Mark Wilson

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