Ancient stars made extraordinarily heavy elements

How heavy can an element be? An international team of researchers has found that ancient stars were capable of producing elements with atomic masses greater than 260, heavier than any element on the periodic table found naturally on Earth. The finding deepens our understanding of element formation in stars.

We are, literally, made of star stuff. Stars are element factories, where elements constantly fuse or break apart to create other lighter or heavier elements.

When we refer to light or heavy elements, we're talking about their atomic mass.

Broadly speaking, atomic mass is based on the number of protons and neutrons in the nucleus of one atom of that element.

The heaviest elements are only known to be created in neutron stars via the rapid neutron capture process, or r-process.

Picture a single atomic nucleus floating in a soup of neutrons.

Suddenly, a bunch of those neutrons get stuck to the nucleus in a very short time period -- usually in less than one second -- then undergo some internal neutron-to-proton changes, and voila!

A heavy element, such as gold, platinum or uranium, forms.

The heaviest elements are unstable or radioactive, meaning they decay over time.

One way that they do this is by splitting, a process called fission.

"The r-process is necessary if you want to make elements that are heavier than, say, lead and bismuth," says Ian Roederer, associate professor of physics at North Carolina State University and lead author of the research.

Roederer was previously at the University of Michigan.

"You have to add many neutrons very quickly, but the catch is that you need a lot of energy and a lot of neutrons to do so," Roederer says.

"We have a general idea of how the r-process works, but the conditions of the process are quite extreme," Roederer says.

"We don't have a good sense of how many different kinds of sites in the universe can generate the r-process, we don't know how the r-process ends, and we can't answer questions like, how many neutrons can you add? Or, how heavy can an element be? So we decided to look at elements that could be made by fission in some well-studied old stars to see if we could start to answer some of these questions."

The team took a fresh look at the amounts of heavy elements in 42 well-studied stars in the Milky Way.

The stars were known to have heavy elements formed by the r-process in earlier generations of stars.

By taking a broader view of the amounts of each heavy element found in these stars collectively, rather than individually as is more common, they identified previously unrecognized patterns.

Those patterns signaled that some elements listed near the middle of the periodic table -- such as silver and rhodium -- were likely the remnants of heavy element fission.

The team was able to determine that the r-process can produce atoms with an atomic mass of at least 260 before they fission.

"That 260 is interesting because we haven't previously detected anything that heavy in space or naturally on Earth, even in nuclear weapon tests," Roederer says.

"But seeing them in space gives us guidance for how to think about models and fission -- and could give us insight into how the rich diversity of elements came to be."

Read more at Science Daily

Pushing the boundaries of chemistry: Properties of heaviest element studied so far measured at GSI/FAIR

An international research team has succeeded in gaining new insights into the chemical properties of the superheavy element flerovium -- element 114 -- at the accelerator facilities of the GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt. The measurements show that flerovium is the most volatile metal in the periodic table. Flerovium is thus the heaviest element in the periodic table that has been chemically studied. With the results, published in the journal Frontiers in Chemistry, GSI confirms its leading position in the study of the chemistry of superheavy elements and opens new perspectives for the international facility FAIR (Facility for Antiproton and Ion Research), which is currently under construction.

Under the leadership of groups from Darmstadt and Mainz, the two longest-lived flerovium isotopes currently known, flerovium-288 and flerovium-289, were produced using the accelerator facilities at GSI/FAIR and were chemically investigated at the TASCA experimental setup. In the periodic table, flerovium is placed below the heavy metal lead. However, early predictions had postulated that relativistic effects of the high charge in the nucleus of the superheavy element on its valence electrons would lead to noble gas-like behavior, while more recent ones had rather suggested a weakly metallic behavior. Two previously conducted chemistry experiments, one of them at GSI in Darmstadt in 2009, led to contradictory interpretations. While the three atoms observed in the first experiment were used to infer noble gas-like behavior, the data obtained at GSI indicated metallic character based on two atoms. The two experiments were unable to clearly establish the character. The new results show that, as expected, flerovium is inert but capable of forming stronger chemical bonds than noble gases, if conditions are suitable. Flerovium is consequently the most volatile metal in the periodic table.

Flerovium is thus the heaviest chemical element whose character has been studied experimentally. With the determination of the chemical properties, GSI/FAIR confirm their leading position in the research of superheavy elements. "Exploring the boundaries of the periodic table has been a pillar of the research program at GSI since the beginning and will be so at FAIR in the future. The fact that a few atoms can already be used to explore the first fundamental chemical properties, giving an indication of how larger quantities of these substances would behave, is fascinating and possible thanks to the powerful accelerator facility and the expertise of the worldwide collaboration," elaborates Professor Paolo Giubellino, Scientific Managing Director of GSI and FAIR. "With FAIR, we are bringing the universe into the laboratory and explore the limits of matter, also of the chemical elements."

Six weeks of experimentation

The experiments conducted at GSI/FAIR to clarify the chemical nature of flerovium lasted a total of six weeks. For this purpose, four trillion calcium-48 ions were accelerated to ten percent of the speed of light every second by the GSI linear accelerator UNILAC and fired at a target containing plutonium-244, resulting in the formation of a few flerovium atoms per day.

The formed flerovium atoms recoiled from the target into the gas-filled separator TASCA. In its magnetic field, the formed isotopes, flerovium-288 and flerovium-289, which have lifetimes on the order of a second, were separated from the intense calcium ion beam and from byproducts of the nuclear reaction. They penetrated a thin film, thus entering the chemistry apparatus, where they were stopped in a helium/argon gas mixture. This gas mixture flushed the atoms into the COMPACT gas chromatography apparatus, where they first came into contact with silicon oxide surfaces. If the bond to silicon oxide was too weak, the atoms were transported further, over gold surfaces -- first those kept at room temperature, and then over increasingly colder ones, down to about -160 °C. The surfaces were deposited as a thin coating on special nuclear radiation detectors, which registered individual atoms by spatially resolved detection of the radioactive decay. Since the decay products undergo further radioactive decay after a short lifetime, each atom leaves a characteristic signature of several events from which the presence of a flerovium atom can unambiguously be inferred.

One atom per week for chemistry

"Thanks to the combination of the TASCA separator, the chemical separation and the detection of the radioactive decays, as well as the technical development of the gas chromatography apparatus since the first experiment, we have succeeded in increasing the efficiency and reducing the time required for the chemical separation to such an extent that we were able to observe one flerovium atom every week," explains Dr. Alexander Yakushev of GSI/FAIR, the spokesperson for the international experiment collaboration.

Six such decay chains were found in the data analysis. Since the setup is similar to that of the first GSI experiment, the newly obtained data could be combined with the two atoms observed at that time and analyzed together. None of the decay chains appeared within the range of the silicon oxide-coated detector, indicating that flerovium does not form a substantial bond with silicon oxide. Instead, all were transported with the gas into the gold-coated portion of the apparatus within less than a tenth of a second. The eight events formed two zones: a first in the region of the gold surface at room temperature, and a second in the later part of the chromatograph, at temperatures so low that a very thin layer of ice covered the gold, so that adsorption occurred on ice.

From experiments with lead, mercury and radon atoms, which served as representatives of heavy metals, weakly reactive metals as well as noble gases, it was known that lead forms a strong bond with silicon oxide, while mercury reaches the gold detector. Radon even flies over the first part of the gold detector at room temperature and is only partially retained at the lowest temperatures. Flerovium results could be compared with this behavior.

Apparently, two types of interaction of a flerovium species with the gold surface were observed. The deposition on gold at room temperature indicates the formation of a relatively strong chemical bond, which does not occur in noble gases. On the other hand, some of the atoms appear never to have had the opportunity to form such bonds and have been transported over long distances of the gold surface, down to the lowest temperatures. This detector range represents a trap for all elemental species. This complicated behavior can be explained by the morphology of the gold surface: it consists of small gold clusters, at the boundaries of which very reactive sites occur, apparently allowing the flerovium to bond. The fact that some of the flerovium atoms were able to reach the cold region indicates that only the atoms that encountered such sites formed a bond, unlike mercury, which was retained on gold in any case. Thus, the chemical reactivity of flerovium is weaker than that of the volatile metal mercury. The current data cannot completely rule out the possibility that the first deposition zone on gold at room temperature is due to the formation of flerovium molecules. It also follows from this hypothesis, though, that flerovium is chemically more reactive than a noble gas element.

International and interdisciplinary collaboration as the key to understanding

The exotic plutonium target material for the production of the flerovium was provided in part by Lawrence Livermore National Laboratory (LLNL), USA. In the Department of Chemistry's TRIGA site at Johannes Gutenberg University Mainz (JGU), the material was electrolytically deposited onto thin titanium foils fabricated at GSI/FAIR. "There is not much of this material available in the world, and we are fortunate to have been able to use it for these experiments that would not otherwise be possible," said Dr. Dawn Shaughnessy, head of the Nuclear and Chemical Sciences Division at LLNL. "This international collaboration brings together skills and expertise from around the world to solve difficult scientific problems and answer long-standing questions, such as the chemical properties of flerovium."

"Our accelerator experiment was complemented by a detailed study of the detector surface in collaboration with several GSI departments as well as the Department of Chemistry and the Institute of Physics at JGU. This has proven to be key to understanding the chemical character of flerovium. As a result, the data from the two earlier experiments are now understandable and compatible with our new conclusions," says Christoph Düllmann, professor of nuclear chemistry at JGU and head of the research groups at GSI and at the Helmholtz Institute Mainz (HIM), a collaboration between GSI and JGU.

How the relativistic effects affect its neighbors, the elements nihonium (element 113) and moscovium (element 115), which have also only been officially recognized in recent years, is the subject of subsequent experiments. Initial data have already been obtained as part of the FAIR Phase 0 program at GSI. Furthermore, the researchers expect that significantly more stable isotopes of flerovium exist, but these have not yet been found. However, the researchers now already know that they can expect to find a metallic element.

Read more at Science Daily

Biologists construct a 'periodic table' for cell nuclei

One hundred fifty years ago, Dmitri Mendeleev created the periodic table, a system for classifying atoms based on the properties of their nuclei. This week, a team of biologists studying the tree of life has unveiled a new classification system for cell nuclei and discovered a method for transmuting one type of cell nucleus into another.

The study, which appears this week in the journal Science, emerged from several once-separate efforts. One of these centered on the DNA Zoo, an international consortium spanning dozens of institutions including Baylor College of Medicine, the National Science Foundation-supported Center for Theoretical Biological Physics (CTBP) at Rice University, the University of Western Australia and SeaWorld.

Scientists on the DNA Zoo team had been working together to classify how chromosomes, which can be several meters long, fold up to fit inside the nuclei of different species from across the tree of life.

"Whether we were looking at worms or urchins, sea squirts or coral, we kept seeing the same folding patterns coming up," said Dr. Olga Dudchenko, co-first author of the new study and a member of the Center for Genome Architecture at Baylor and CTBP.

Eventually, the team realized it was just seeing variants on two overall nuclear designs. "In some species, chromosomes are organized like the pages of a printed newspaper, with the outer margins on one side and the folded middle at the other," explained Dudchenko, who also is co-director of DNA Zoo. "And then in other species, each chromosome is crumpled into a little ball."

"So we had a puzzle," said Dr. Erez Lieberman Aiden, an associate professor of molecular and human genetics and Emeritus McNair Scholar at Baylor, co-director of the DNA Zoo and senior author on the new study. "The data implied that over the course of evolution, species can switch back and forth from one type to the other. We wondered: What is the controlling mechanism? Might it be possible to change one type of nucleus into another in the lab?" Aiden also is director of the Center for Genome Architecture and a senior investigator at CTBP.

Meanwhile, an independent team in the Netherlands had discovered something unexpected. "I was doing experiments on a protein called condensin II, which we knew plays a role in how cells divide," said Claire Hoencamp, co-first author of the study and a member of the laboratory of Dr. Benjamin Rowland at the Netherlands Cancer Institute. "But we observed the strangest thing: When we mutated the protein in human cells, the chromosomes would totally rearrange. It was baffling!"

The two teams met at a conference in the Austrian mountains, where Rowland presented his lab's latest work. They soon realized that Hoencamp had hit on a way to convert human cells from one nuclear type to another.

"When we looked at the genomes being studied at the DNA Zoo, we discovered that evolution had already done our experiment many, many times! When mutations in a species break condensin II, they usually flip the whole architecture of the nucleus," said Rowland, senior author on the study. "It's always a little disappointing to get scooped on an experiment, but evolution had a very long head start."

The team decided to work together to confirm condensin II's role. But then the COVID-19 pandemic struck, and much of the world shut down.

"Without access to our laboratories, we were left with only one way to establish what condensin II was doing," Hoencamp said. "We needed to create a computer program that could simulate the effects of condensin II on the chain of hundreds of millions of genetic letters that comprise each human chromosome."

The team turned to Dr. José Onuchic, the Harry C. and Olga K. Wiess Chair of Physics at Rice. "Our simulations showed that by destroying condensin II, you could make a human nucleus reorganize to resemble a fly nucleus," said Onuchic, co-director of CTBP, which includes collaborators at Rice, Baylor, Northeastern University and other institutions in Houston and Boston.

The simulations were performed by a team within Onuchic's lab at CTBP, led by postdoctoral fellow and co-first author Dr. Sumitabha Brahmachari, working with Dr. Vinicius Contessoto, a former postdoc at CTBP, and Dr. Michele Di Pierro, a CTBP senior investigator and currently an assistant professor at Northeastern University.

"We began with an incredibly broad survey of 2 billion years of nuclear evolution," Brahmachari said. "And we found that so much boils down to one simple mechanism, that we can simulate as well as recapitulate, on our own, in a test tube. It's an exciting step on the road to a new kind of genome engineering -- in 3D!"

Read more at Science Daily

Discoveries at the edge of the periodic table: First ever measurements of einsteinium

 Since element 99 -- einsteinium -- was discovered in 1952 at the Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) from the debris of the first hydrogen bomb, scientists have performed very few experiments with it because it is so hard to create and is exceptionally radioactive.A team of Berkeley Lab chemists has overcome these obstacles to report the first study characterizing some of its properties, opening the door to a better understanding of the remaining transuranic elements of the actinide series.

Published in the journal Nature, the study,"Structural and Spectroscopic Characterization of an Einsteinium Complex,"was co-led by Berkeley Lab scientist Rebecca Abergel and Los Alamos National Laboratory scientist Stosh Kozimor, and included scientists from the two laboratories, UC Berkeley, and Georgetown University, several of whom are graduate students and postdoctoral fellows. With less than 250 nanograms of the element, the team measured the first-ever einsteinium bond distance, a basic property of an element's interactions with other atoms and molecules.

"There's not much known about einsteinium," said Abergel,who leads Berkeley Lab'sHeavy Element Chemistry groupand is an assistant professor in UC Berkeley's Nuclear Engineering department. "It's a remarkable achievement that we were able to work with this small amount of material and do inorganic chemistry. It's significant because the more we understand about its chemical behavior, the more we can apply this understanding for the development of new materials or new technologies, not necessarily just with einsteinium, but with the rest of the actinides too. And we can establish trends in the periodic table."

Short-lived and hard to make

Abergel and her team used experimental facilities not available decades ago when einsteinium was first discovered -- theMolecular Foundryat Berkeley Lab and theStanford Synchrotron Radiation Lightsource (SSRL)at SLAC National Accelerator Laboratory, both DOE Office of Science user facilities -- to conduct luminescence spectroscopy and X-ray absorption spectroscopy experiments.

But first, getting the sample in a usable form was almost half the battle. "This whole paper is a long series of unfortunate events," she said wryly.

The material was made at Oak Ridge National Laboratory's High Flux Isotope Reactor, one of only a few places in the world that is capable of making einsteinium, which involves bombarding curium targets with neutrons to trigger a long chain of nuclear reactions. The first problem they encountered was that the sample was contaminated with a significant amount of californium, as making pure einsteinium in a usable quantity is extraordinarily challenging.

So they had to scrap their original plan to use X-ray crystallography -- which is considered the gold standard for obtaining structural information on highly radioactive molecules but requires a pure sample of metal -- and instead came up with a new way to make samples and leverage element-specific research techniques. Researchers at Los Alamos provided critical assistance in this step by designing a sample holder uniquely suited to the challenges intrinsic to einsteinium.

Then, contending with radioactive decay was another challenge. The Berkeley Lab team conducted their experiments with einsteinium-254, one of the more stable isotopes of the element. It has a half-life of 276 days, which is the time for half of the material to decay. Although the team was able to conduct many of the experiments before the coronavirus pandemic, they had plans for follow-up experiments that got interrupted thanks to pandemic-related shutdowns. By the time they were able to get back into their lab last summer, most of the sample was gone.

Bond distance and beyond

Still, the researchers were able to measure a bond distance with einsteinium and also discovered some physical chemistry behavior that was different from what would be expected from the actinide series, which are the elements on the bottom row of the periodic table.

"Determining the bond distance may not sound interesting, but it's the first thing you would want to know about how a metal binds to other molecules. What kind of chemical interaction is this element going to have with other atoms and molecules?" Abergel said.

Once scientists have this picture of the atomic arrangement of a molecule that incorporates einsteinium, they can try to find interesting chemical properties and improve understanding of periodic trends. "By getting this piece of data, we gain a better, broader understanding of how the whole actinide series behaves. And in that series, we have elements or isotopes that are useful for nuclear power production or radiopharmaceuticals," she said.

Tantalizingly, this research also offers the possibility of exploring what is beyond the edge of the periodic table, and possibly discovering a new element. "We're really starting to understand a little better what happens toward the end of the periodic table, and the next thing is, you could also envision an einsteinium target for discovering new elements," Abergel said. "Similar to the latest elements that were discovered in the past 10 years, like tennessine, which used a berkelium target, if you were to be able to isolate enough pure einsteinium to make a target, you could start looking for other elements and get closer to the (theorized)island of stability," where nuclear physicists have predicted isotopes may have half-lives of minutes or even days, instead of the microsecond or less half-lives that are common in the superheavy elements.

Read more at Science Daily

Periodic table still influencing today's research

The periodic table is still influencing research today.

This year marks the 150th anniversary of the Periodic Table, and the principles that drove Dmitri Mendeleev to construct his table are still influencing today's research advances.

In a special issue of Science, which celebrates this sesquicentennial anniversary, a Michigan State University scientist highlights some of the current research around the globe driven by Mendeleev's influence.

"Our goal was to showcase contemporary research being pursued around the world, including U.S. Department of Energy-supported research at MSU, that's working to realize new approaches to photoinduced chemical processes," said James McCusker, MSU chemist and review author.

McCusker's contribution focused on the process of light absorption that incorporates elements from the so-called "transition block" of the Periodic Table. Compounds from this class are involved in everything from solar energy conversation to organic synthesis.

"The effective capture and use of sunlight -- an inexhaustible, globally accessible and pollution-free energy source -- is critical for replacing fossil fuels and in mitigating climate change," McCusker said. "In order to realize this goal, one of the key processes that must occur following the absorption of light is the transfer of electrons, similar to what plants do in photosynthesis."

But unleashing this capability has proved challenging. That's due, in part, to the fact that the compounds that are very effective at converting light into useable charge require the use of some of the least-abundant elements on the planet. Take for example ruthenium and iridium, which are widely employed in chromophores that can carry out these light-enabled chemical processes.

"Ruthenium is one of the five or six least-abundant elements in Earth's crust and is simply not a viable option as the light-harvesting component for a globally scaled problem like solar fuel production," McCusker said. "We need to find replacements that are abundant on Earth, such as iron, to make global scalability possible. This is not an engineering or manufacturing problem, but one of fundamental science that has its origins in the very concepts that Mendeleev uncovered when he constructed the periodic table."

That's where some of MSU's DOE-supported research comes into play. McCusker's research is based on a confluence of synthetic organic and inorganic chemistries as well as a range of spectroscopic techniques.

"Of particular importance with regard to our solar energy conversion efforts is ultrafast time-resolved laser spectroscopy, which allows us to track the evolution of a chemical system less than one trillionth of a second after light has been absorbed," McCusker said. "The ability to combine synthesis and ultrafast spectroscopy in one laboratory is a critically important aspect of the research since it allows my students and I to make immediate connections between the composition of the molecules we prepare and their light-induced properties."

Read more at Science Daily