Reaching for Neutron Star

Scientists found the predictive framework, thick skin of atomic nucleus.

Reaching for Neutron Star
Crab Nebula in the constellation Taurus contains a pulsar at its core that is a younger neutron star, the very type brought into clearer focus by a Physics Review Letters study by researchers at Washington University in St. Louis. Elements of this image are furnished by NASA. (Photo: Shutterstock)

Its been more than a decade, Scientists at the Washington University in St. Louis is following the atomic nucleus. With continuous advancements in studies, they now moved up the element chain to Calcium-48.

Calcium-48 is an uncommon strong item that has a bigger number of neutrons than protons. Moreover, it conveys a weighty sticker price of $100,000 per gram.

Co-author Charity, a research professor of chemistry in Arts & Sciences said, “If you leave it on a table, it turns to powder. Calcium oxidizes very quickly in air. It was a worry.”

Scientists used 3 grams of Calcium-48 and discovered both a framework that foresee where neutrons will occupy the nucleus and an approach to anticipating the skin thickness of the nucleus. By predicting how the neutrons would create a thick skin, they showed that this skin of Ca-48 — 3.5 femtometers (fm) in radius — measured 0.249 + 0.023 fm.

Scientists noted, “the skin is thicker and more neutron-rich than previously believed.”

Co-author Willem H. Dickhoff said, “That links us to astrophysics and, in particular, neutron star physics. The Los Alamos experiment was critical for the analysis we pursued. In the end, because it has this additional set of neutrons, it gets us to information that helps us to further clarify the physics of neutron star, where there are many more neutrons relative to protons.”

“And it gives us the opportunity to predict where the neutrons are in Ca-48. That is the critical information, which leads to the prediction of the neutron skin.”

Scientists later observed how Ca-48 is undergoing the cleanest skin-thickness test available via the electron accelerator. Furthermore, they proceed to move up the element chain of neutron-rich nuclei to the ‘famous nucleus’ of Lead-208.

In other words, they observed all energies simultaneously rather than focusing on one single energy.

For further observation, they used dispersive optical model (DOM). They expanded upon it — across energy domains and isotopes — so they could attempt to predict where the nuclear particles are.

Charity explained, “Heavy neutron-rich elements behave differently. So this team keeps ascending the heavyweight classes: Ca-40, Ca-48, Lead-208. How far can you go out along an isotope chain until losing neutrons? It gives them skin in the skin game.”

“When you put extra neutrons in, it doesn’t like that, right? It has to figure out how to accommodate these extra neutrons. It can put them evenly throughout the nucleus. Or it could put them on the surface. So the question is: Is this force stronger in the low-density region of the nucleus or weaker?”

Dickhoff said, “We know where the protons are. That is well established experimentally. But you can’t do that easily with neutrons. I simply want to know what a nucleon, a proton or a neutron, is doing. How is it spending its time? Nucleons are more interactive — they do other things than sit quietly in their orbits. That’s what this method can sort of tell us.”

“Through the DOM framework, we made a prediction that is well founded and taken seriously. Next, we will have a measurement for Lead-208.”