New measurements of exotic form of magnesium suggest surprising shape-shift


This instrumentation at Japan’s Radioactive Isotope Beam Factory in Wako, Japan, was utilized in an experiment to develop an exotic magnesium isotope. Credit: RIKEN Nishina Center for Accelerator-Based Science

Simply over a years ago researchers pressed magnesium atoms to new limitations, jamming additional neutrons into their nuclei towards—and perhaps reaching—the optimum limitation for this aspect.


Now, a global group led by researchers at the Department of Energy’s Lawrence Berkeley National Lab (Berkeley Laboratory) has actually replicated this exotic system, called magnesium-40, and obtained new and surprising ideas about its nuclear structure.

“Magnesium-40 sits at an intersection where there are a lot of questions about what it really looks like,” stated Heather Crawford, a personnel researcher in the Nuclear Science Department at Berkeley Laboratory and lead author of this research study, released online Feb. 7 in the Physical Evaluation Letters journal. “It’s an extremely exotic species.”

While the number of protons (which have a favorable electrical charge) in its atomic nucleus specifies a component’s atomic number—where it rests on the table of elements—the number of neutrons (which have no electrical charge) can vary. The most typical and steady type of magnesium atom discovered in nature has 12 protons, 12 neutrons, and 12 electrons (which have an unfavorable charge).

Atoms of the very same aspect with various neutron counts are called isotopes. The magnesium-40 (Mg-40) isotope that the scientists studied has 28 neutrons, which might be the optimum for magnesium atoms. For a provided aspect, the optimum number of neutrons in a nucleus is described as the “neutron drip line—if you try to add another neutron when it is already at capacity, the extra neutron will immediately “drip” out of the nucleus.

“It’s extremely neutron-rich,” Crawford stated. “It’s not known if Mg-40 is at the drip line, but it’s surely very close. This is one of the heaviest isotopes that you can currently reach experimentally near the drip line.”

The shape and structure of nuclei near the drip line is especially intriguing to nuclear physicists due to the fact that it can teach them basic features of how nuclei act at the extremes of presence.

“The interesting question in our minds all along, when you get so close to the drip line, is: ‘Does the way that the neutrons and protons arrange themselves change?'” stated Paul Fallon, a senior researcher in Berkeley Laboratory’s Nuclear Science Department and a co-author of the research study. “One of the major goals of the nuclear physics field is to understand the structure from the nucleus of an element all the way to the drip line.”

Such a basic understanding can notify theories about explosive procedures such as the production of heavy aspects in star mergers and surges, he stated.

The research study is based upon experiments at Japan’s Radioactive Isotope Beam Factory (RIBF), which lies at the RIKEN Nishina Center for Accelerator-Based Science in Wako, Japan. Scientist integrated the power of 3 cyclotrons—a type of particle accelerator initially established by Berkeley Laboratory creator Ernest Lawrence in 1931—to produce very-high-energy particle beams taking a trip at about 60 percent of the speed of light.

New measurements of exotic form of magnesium suggest surprising shape-shift
An image of the secondary beam “cocktail” produced at a cyclotron center in Japan for a research study of Mg-40, an exotic isotope of magnesium. The X axis reveals the mass-to-charge provision, and the Y axis reveals the atomic number. This image was included on the cover of the journal Physical Evaluation Letters. Credit: H.L. Crawford et al., Phys. Rev. Lett. 122, 052501, 2019

The research study group utilized an effective beam of calcium-48, which is a steady isotope of calcium with a magic number of both protons (20) and neutrons (28), to strike a turning disk of several-millimeters-thick carbon.

Some of the calcium-48 nuclei crashed into the carbon nuclei, sometimes producing an aluminum isotope called aluminum-41. The nuclear physics experiment separated out these aluminum-41 atoms, which were then carried to strike a centimeters-thick plastic (CH2) target. The effect with this secondary target knocked a proton far from some of the aluminum-41 nuclei, developing Mg-40 nuclei.

This 2nd target was surrounded by a gamma-ray detector, and scientists had the ability to examine ecstatic states of Mg-40 based upon the measurements of the gamma rays given off in the beam-target interactions.

In addition to Mg-40, the measurements likewise caught the energies of ecstatic states in other magnesium isotopes, consisting of Mg-36 and Mg-38.

“Most models said that Mg-40 should look very similar to the lighter isotopes,” Crawford stated. “But it didn’t. When we see something that looks very different, then the challenge is for new theories to capture all of this.”

Due to the fact that the theories now disagree with what was seen in the experiments, new estimations are required to discuss what is altering in the structure of Mg-40 nuclei compared to Mg-38 and other isotopes.

Fallon stated that numerous estimations suggest that Mg-40 nuclei are really warped, and perhaps football-shaped, so the 2 included neutrons in Mg-40 might be buzzing around the core to form a so-called halo nucleus instead of being integrated into the shape displayed by surrounding magnesium isotopes.

“We speculate on some of the physics, but this has to be confirmed by more detailed calculations,” he stated.

Crawford stated that extra measurements and theory deal with Mg-40, which close-by isotopes might assist to favorably determine the shape of the Mg-40 nucleus, and to discuss what is triggering the modification in nuclear structure.

Scientists kept in mind that the nuclear physics Center for Rare Isotope Beams, a new DOE Workplace of Science User Center that is under building at Michigan State University, integrated with the Gamma-Ray Energy Tracking Range (GRETA) being developed at Berkeley Laboratory, will allow more research studies of other aspects near the nuclear drip line.


Check Out even more:
Observation of all of a sudden warped neutron-rich magnesium nuclei triggers rethink of nuclear shell structure

More details:
H. L. Crawford et al, First Spectroscopy of the Near Drip-line Nucleus Mg40, Physical Evaluation Letters (2019). DOI: 10.1103/PhysRevLett.122.052501

Journal referral:
Physical Evaluation Letters

Supplied by:
Lawrence Berkeley National Lab

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