Reaching for neutron stars: Research group finds predictive framework, thick skin of atomic nucleus

November 30, 2017 by Chuck Finder, Washington University in St. Louis
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. Credit: Shutterstock

For more than a decade, a cross-disciplinary team of chemists and physicists in Arts & Sciences at Washington University in St. Louis has been chasing the atomic nucleus. With progressive studies, they moved up the element chain to Calcium-48, an extremely rare solid commodity that has more neutrons than protons and, as such, carries a hefty price tag of $100,000 per gram.

It is a quirky material, with this particular study taking Washington University chemists Robert J. Charity and Lee G. Sobotka from Duke's Triangle Universities Nuclear Laboratory to the Department of Energy's Los Alamos (N.M.) National Laboratory.

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

Ultimately, three grams of Ca-48 helped to produce a double-edged finding for Charity and co-author Willem H. Dickhoff, professor of physics. Their team discovered both a framework to predict where neutrons will inhabit a nucleus and a way to predict the thickness of a nucleus.

In their research published Nov. 29 in Physical Review Letters, they predicted how the neutrons would create a thick skin, and that this skin of Ca-48—3.5 femtometers (fm) in radius—measured 0.249 + 0.023 fm.

To convert that into centimeters, it would measure 2.49×10-14 cm. The researchers say the key finding is that the skin is thicker and more -rich than previously believed.

"That links us to astrophysics and, in particular, neutron-star physics," Dickhoff said of the research results. "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 stars, where there are many more neutrons relative to protons.

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

For Charity, Dickhoff and co-authors Hossein Mahzoon, PhD '15, a lecturer in physics at Truman State University in Kirksville, Mo., and Mack Atkinson, a PhD candidate in physics at Washington University, the chase continues.

They watch with interest as Ca-48 is scheduled to undergo the cleanest skin-thickness test available via the electron accelerator at the Thomas Jefferson National Accelerator Facility in Newport News, Va.

Moreover, they proceed to move up the element chain of neutron-rich nuclei to what Charity called the "famous nucleus" of Lead-208. Michael Keim, a senior in physics, is spearheading a study of Lead-208.

"It will give us an experimental handle on whether our analysis is really predictive," Dickhoff said. "We think we have a good argument why we think it has a thick skin. There is a large group of people … who predict a smaller skin. This is directly relevant for the understanding of the size of . It is not yet crystal clear how big a neutron star is—its radius."

How they made their analysis and reached this predictive framework is part of their decade-long pursuit as well. Their chemistry-physics group subscribes to "dispersion relations," which Sobotka, who is a professor of chemistry and of physics, explained simply: "It's what tells you not to laugh before you are tickled. That means causality is properly taken into account."

In short, they analyze all energies simultaneously rather than focusing on one single energy.

Since first publishing together in 2006, they have used the dispersive optical model (DOM) developed a quarter-century ago by Claude Mahauxa, a nuclear theorist from Belgium. They expanded upon it—across energy domains and isotopes—so they could attempt to predict where the nuclear particles are.

"We had to make the technical step to include the sensitivities of particles," Dickhoff said. He used his hands to illustrate the center and then the rest of a nucleus: "If they are here, they were also influenced by everywhere else. Which we call 'nonlocality.' Without that, you cannot make these predictions."

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?" Charity said. It gives them skin in the skin game.

"When you put extra neutrons in, it doesn't like that, right?" Charity said of the . "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?"

"We know where the protons are," Dickhoff added. "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."

Their nonlocal DOM framework—a decade-plus in the making—uses computer modeling and computations as well as the lab experimentation. It allows them to "make a prediction that is well founded and taken seriously," Dickhoff said. "Next, we will have a measurement for Lead-208."

Explore further: Researchers study unusual and extremely short-lived species of hydrogen

More information: Neutron Skin Thickness of 48Ca from a Nonlocal Dispersive Optical-Model Analysis. Phys. Rev. Lett. doi.org/10.1103/PhysRevLett.119.222503

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19 comments

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Chris_Reeve
Nov 30, 2017
This comment has been removed by a moderator.
jonesdave
3.9 / 5 (7) Nov 30, 2017
Parker, E. N., Reflections on Macrophysics and the Sun, Solar Physics 176: 1997, p.219-247


This would be the same E.N. Parker who authored this?

The Solar-Flare Phenomenon and the Theory of Reconnection and Annihiliation of Magnetic Fields. (1963)
http://adsabs.har....8..177p

Chris_Reeve
Nov 30, 2017
This comment has been removed by a moderator.
jonesdave
5 / 5 (5) Nov 30, 2017
Ah, you got me. I forgot that people who are one time correct are ALWAYS correct. Please forgive, the world is simpler than I have imagined.

/sarc


F***d up, didn't you Christopher? Parker-Sweet? Magnetic reconnection? Lol.
Chris_Reeve
Nov 30, 2017
This comment has been removed by a moderator.
Nik_2213
5 / 5 (5) Nov 30, 2017
So Parker was very wrong ??
jonesdave
5 / 5 (4) Nov 30, 2017
(/sarc means sarcasim, jonesdave)


And you just quoted a bloke who was essentially one of the founders of MRx! Along with Dungey. Tell me again; what is the EU stance on MRx? Hypocrisy, much?
cantdrive85
1 / 5 (5) Nov 30, 2017
jonesdumb can't grasp that someone can be both right about some things and dreadfully wrong about others. Newton spent much of his life pontificating upon alchemy and the occult. He also stated;
"Gravity explains the motions of the planets, but it cannot explain who set the planets in motion. God governs all things and knows all that is or can be done."
So jonesdumb, is he right about everything or nothing? Moron!
Captain Stumpy
5 / 5 (3) Dec 01, 2017
@idiot pseudoscience eu cult member chris/hannes
(/sarc means sarcasim, jonesdave)
[sic]
for starters, it is "sarcasm" - spell check is free

for two, the most important thing in your paragraph you idiotically posted was the following word: "Reflections"

IOW - these are his personal opinions, also known as a Self-report or attitudinal statement
http://www.auburn...ion.html

by definition, it is not fact but a subjective perspective
it also cannot be all-inclusive nor definitive of all reality

had you even been topically familiar with the scientific method you would notice that this author is speaking directly about why the eu idiots cling to their "seriously and often passionately held" beliefs when there is direct validated evidence proving them wrong, such as reconnection

[not sarc]
yep
1 / 5 (3) Dec 02, 2017
@captain hypocrite consensus stooge ignorant of history
Direct validated evidence? Like connections between high redshifted and low redshifted galaxies?
Your main stream pseudoscience faith based in a miracle is weak sauce full of dark matter nonsense and defies physics and common sense.
antialias_physorg
5 / 5 (1) Dec 02, 2017
an extremely rare solid commodity that has more neutrons than protons

Just to clarify this: Having more neutrons than protons is not what makes an element a rare commodity. Every element heavier than calcium has more neutrons than protons (and some lighter ones, too).
What makes Ca-48 rare is that it has 8 more neutrons than calcium usually does.
Da Schneib
not rated yet Dec 02, 2017
@mac is arguing against data again.
Da Schneib
not rated yet Dec 02, 2017
@mac you just made a counter-claim against the claims of the current article. The claims in the current article are based not solely upon simulations, but also upon measurements, that is, data. You oppose a two-year-old article based only on simulations.

You're arguing against data again precisely as I said.
Da Schneib
not rated yet Dec 02, 2017
@mac, if you're wrong it's not my problem. I just point it out. Your problem is you keep being wrong the same way.

A preprint version of the article is available on arXiv at: https://arxiv.org...6719.pdf

Figures 1 and 2 are particularly of note since they both show experimental data to compare with the simulations and check their accuracy.
Da Schneib
1 / 5 (1) Dec 02, 2017
@mak double magic nuclei are only tools in this experiment. They're experimental equipment. Are you now arguing against using experimental equipment? Maybe you think we should all learn by osmosis, or meditation, or nationalism, or bigotry, or books by stone age sheep herders, or something.
Captain Stumpy
5 / 5 (1) Dec 02, 2017
@yep, you're still a pseudoscience idiot cult member
Direct validated evidence? Like connections between
wow!
apparently, you missed the whole MRx debate your idiot cult has repeatedly posted everywhere on the web!

perhaps you should read up before commenting further?
Ah, never mind! You're in a cult so that will never happen!
high redshifted and low redshifted galaxies?
just because you don't understand it doesn't mean no one else does
Your main stream pseudoscience faith based in a miracle is weak sauce full of dark matter nonsense and defies physics and common sense
[sic]
again - just because you don't understand doesn't mean no one does

this is for you as a starter to learning about science - the foundation is necessary before you move on to the hard stuff: http://www.readingbear.org/
milnik
1 / 5 (2) Dec 03, 2017
Again, one more proof is that science does not know the structure of the universe. From here it can be seen that the science and the sequence of the formation of celestial bodies are not known in science, and therefore they are trying to do something that will resemble a neutron star. This can not be achieved at our level or on any planet.
I will help you:
The order of formation of celestial bodies: the formation of a quark gluon plasma from the substance AETHER, which is filled with an infinite universe, a magnetar, a pulsar, a neutron star, supernova, gas gowns, celestial bodies like planets and suns, and when critical mass and critical gravity on certain groups of matter, then there is a black hole in which matter returns to the form of Aether from which matter is formed, These are renewable cycles.
milnik
1 / 5 (2) Dec 03, 2017
Again, one more proof is that science does not know the structure of the universe. From here it can be seen that the science and the sequence of the formation of celestial bodies are not known in science, and therefore they are trying to do something that will resemble a neutron star. This can not be achieved at our level or on any planet.
I will help you:
The order of formation of celestial bodies: the formation of a quark gluon plasma from the substance AETHER, which is filled with an infinite universe, a magnetar, a pulsar, a neutron star, supernova, gas gowns, celestial bodies like planets and suns, and when critical mass and critical gravity on certain groups of matter, then there is a black hole in which matter returns to the form of Aether from which matter is formed, These are renewable cycles.
milnik
1 / 5 (2) Dec 03, 2017
Secondly, what are neutrons and how do they occur? When forming matter in the form of a "solid state", a particle of 3kg (3 quarts and three gluon binders) is formed, and the deposition "liquid state" of matter-free gluons is formed.
When a gluon occurs in a 3kg particle, a neutron occurs, and when the gluon decays in the neutron, then the electrons begin to circulate around the remainder (proton) and the first atom is formed.
Are you satisfied with the education?

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