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Performing Chemistry in Floating Droplets

Performing Chemistry in Floating Droplets

Could chemists be ready to ditch the venerable test tube, the very symbol of chemistry in the minds of many people? Maybe not quite yet, but Caltech’s Jack Beauchamp is working on it.

Beauchamp is doing work in what he calls “lab-in-a-drop” chemistry, in which chemical reactions are performed within a drop of liquid suspended in midair through acoustic levitation.

Acoustic levitation works by creating areas of high and low pressure in the air through the use of ultrasonic transducers. These transducers act like tiny but powerful speakers that operate at a frequency above what human ears can hear. The sonic energy emitted by these transducers is focused in such a way that the high- and low-pressure zones they create form “traps” that can hold small objects in place in the air. An object placed in one of the low-pressure zones is held there by the high-pressure zones that surround it. An acoustic levitator of this sort can be constructed for about $75 from off-the-shelf parts using 3D-printing techniques.

An animated gif showing a hand place a pellet in the levitator. Graphics showing high- and low-pressure zones are superimposed.

Credit: Caltech

In a new paper, Beauchamp and his colleagues describe the use of the technique to study how a skin-cancer drug works at a chemical level. The research, he says, represents the first successful use of acoustic levitation as a “wall-less” reactor in a detailed study of chemical reactions.

In the work, Beauchamp and his team coated a droplet of water with lipids, biomolecules that make up cell membranes. They then applied an anti-cancer drug to the droplet and used a mass spectrometer to “sniff” the chemical signature given off by the droplet as the drug reacted with the lipid when illuminated with a red laser pointer.

In the experiment, the researchers added a small amount of one of two lipids, cardiolipin and POPG (1-palmitoyl-2-oleoyl-sn-glycero-3-phospho-(1′-rac-glycerol)), to each drop of water. The lipids migrated to the surface of the droplet, where they organized to form a thin film that is similar in composition to the cell membrane of a living cell.

With the membrane established, a chemical called temoporfin was added to the droplet. Temoporfin, a ring-like molecule, is excited by red light. In this state, the temoporfin transfers energy to molecular oxygen, forming an excited electronic state that easily oxidizes molecules it comes into contact with, including those that make up cell membranes. This makes temoporfin useful as a treatment for some skin cancers. A doctor could apply the drug to a cancerous lesion and then illuminate it with red light, which easily shines through tissues. As the compound is illuminated and excited, it oxidizes vital cellular materials, including lipids, proteins, and nucleic acids, triggering cell death.

It was this cancer-killing process that Beauchamp wanted to study. “When you’re doing this chemistry, you’d like to be able to carry out these reactions under conditions where you don’t have any contact of the liquid with surfaces,” he says. “We achieve this goal by performing chemistry in a levitated droplet.”

The acoustic levitator allowed Beauchamp and his team to suspend in midair a 1 millimeter droplet of water containing a mixture of the lipid and temoporfin. The droplet was then illuminated by red laser light, exciting the temoporfin and causing it to oxidize the molecules of the membrane layer.

As this oxidation was occurring, a pair of high-voltage electrodes placed near the droplet pulled minute amounts of material off the droplet and into the sensor of a mass spectrometer, which provided readings that allowed researchers to deduce the molecular structures of compounds within the drop. By continually monitoring these readings, the researchers were able to see how the compounds on the surface became progressively more oxidized. By looking at these reaction products, Beauchamp says the research team could determine how the oxidation processes work.

“As far as I know, we’re the only people doing serious chemistry this way, examining the kinetics and mechanism of the reactions involved” Beauchamp says.

Acoustic levitation could find use in other fields as well, he says. As an example, he cites the research of Caltech’s Joe Parker, an assistant professor of biology and biological engineering who studies the symbiotic relationship between certain species of ants and beetles. Beauchamp says it would be possible to levitate an ant and a beetle in close proximity to one another and then use the apparatus to analyze the pheromones they emit.

The technique could have other applications as well. In collaborative studies with Caltech’s John Seinfeld, Louis E. Nohl Professor of Chemical Engineering, Beauchamp previously revealed details of the complex environmental chemistry that leads to the formation of organic aerosols in the atmosphere in studies using droplets hanging on the end of a capillary. With the new levitation methodology, that capillary would no longer be required.

The paper describing Beauchamp’s research, titled “Mass Spectrometric Study of Acoustically Levitated Droplets Illuminates Molecular-Level Mechanism of Photodynamic Therapy for Cancer Involving Lipid Oxidation,” appears in the April 23 issue of Angewandte Chemie, the flagship journal of the German Chemical Society. Beauchamp’s co-authors include Chaonan Mu, Jie Wang, and Xingxing Zhang of Nankai University, and Kevin J. Barraza, a postdoctoral scholar in chemistry at Caltech.

Materials provided by the California Institute of Technology

Atomic motion while nucleation captured in 4-D for the first time

Researchers successful in capturing atomic motion in 4D for the first time

Transformations of physical states such as freezing, melting or evaporation begin with a process known as nucleation. In this step, several tiny clusters of molecules begin to coalesce. Nucleation is a very crucial step in diverse circumstances such as cloud formation or the onset of any neurodegenerative disease.

A group of researchers from UCLA have been successful in getting a view of nucleation – which has never been observed before. It depicts the arrangement of atoms in four-dimensional atomic resolution( three space and one time dimension). The study has been published in the Nature journal and it differs a lot from the statements of the classical theory of nucleation mentioned in textbooks.

Jianwei “John” Miao, a professor of physics and astronomy at UCLA, also the lead author of the study mentioned that this has been a historic achievement as researchers not only could locate the individual atoms but also monitor the real-time motion in 4D. Jianwei Miao is also the deputy director of the STROBE National Science Foundation Science and Technology Center.

Scientists from universities such as the University of Colorado, Boulder, University of Buffalo and University of Nevada, Reno collaborated to build a powerful and effective imaging technique previously developed by the research group of Miao. This is called atomic electron tomography and it uses the highly advanced electron microscope located at Molecular Foundry in Berkeley Lab. It captures a sample using electrons and then the sample is rotated to create amazing 3D images of atoms in a way similar to CAT scan.

For the process, researchers took nanoparticles of an iron-platinum alloy and heated it to 520 degrees Celsius. They took the images after an interval of 9 minutes, 16 minutes and 26 minutes. This temperature marks the transition of alloy between different solid phases.

Even though the alloy looks similar in both phases, a deeper look reveals different 3D arrangements. Due to heating, the structure changes from a haphazard arrangement to a more ordered one. The phase change is similar to the process of solving a Rubik’s cube, where the solved cube has arranged colours unlike the random arrangement of the unsolved one.

Scientists tracked a group of 33 nuclei for observing the change. Through this painstaking process, they found out that nuclear formed irregular shapes as opposed to round shapes predicted by the classical theory. The nuclei do not have a sharp boundary but they possess jumbled arrangement closer to the surface.

Classical nucleation theory also states that once a nucleus reaches a specific size, it only grows larger from there. But the process seems to be far more complicated than that: In addition to growing, nuclei in the study shrunk, divided and merged; some dissolved completely.

These diversions from the classical nucleation theory can open up a new area of study of chemical and biological phenomena.

Researchers pioneer method to purify water using solar energy

Researchers pioneer method to purify water using solar energy

As the global population grows, fresh water supplies are more precious than ever. While scientists and engineers know how to purify water, making those methods sustainable and energy efficient is another question.

One promising approach is solar-driven distillation, or solar steam generation, which can help us get fresh water from wastewater or seawater. Researchers have used this method to successfully distill small batches of purified water, but they are still searching for a way to do this on a large scale.

Researchers at the University of Chicago’s Pritzker School of Molecular Engineering and UChicago-affiliated Argonne National Laboratory were part of a team that developed a pioneering new method of solar steam generation that could help bring this technology into the real world. The materials can be grown on top of wood, fabric or sponges in an easy, one-step process, and show promise for large-scale manufacturing.

“Solar steam generation techniques are still mostly focused on lab use now,” said Zijing Xia, a graduate student at Pritzker Molecular Engineering and lead author of the research. “We want to find an easy way to fabricate solar steam generators at relatively low cost.”

The results of their innovative work were recently published in the journal Advanced Materials Interfaces.

“We want to find an easy way to fabricate solar steam generators at relatively low cost.”

—Graduate student and study lead author Zijing Xia

In the search for solar steam systems, researchers have already tried various materials which convert light to heat, such as carbon materials, plasmonic metals and semiconductors. But many of these options have relatively low efficiency, among other challenges, and so the search continues for a truly transformative method.

A high-performance solar steam generator will ideally combine several characteristics. It should be buoyant on water, be able to absorb a broad spectrum of light, convert light to heat efficiently and be able to transfer that heat to water. Unfortunately, many previously studied methods lack the porous structure needed to facilitate the heat transfer to water.

“Most existing methods cannot be easily engineered to produce steam-generating devices with both arbitrary control over the shape and high photothermal efficiency,” Xia said.

What sets Xia’s method apart is the use of a porphyrin covalent organic framework, or POF. A newly discovered class of materials, POFs can grow uniformly on the surface of a variety of materials with different levels of porosity, and they show high performance for water evaporation. POFs also have unique light-harvesting characteristics beneficial for new applications.

In the lab, POFs successfully grew on the inner and outer surfaces of every tested material. And every template showed favorable photothermal properties, indicating that POF-based materials are promising candidates for solar steam generation. The POF membrane was able to capture more than 95% of light across the majority of the spectrum of sunlight.

The most promising result of the research, Xia said, was the POFs’ ability to grow at the surface of many different kinds of materials, including membranes, fabrics, sponges and wood. The wood showed particularly strong performance, with researchers measuring roughly 80% light-to-steam conversion efficiency.

Solar Steam Illustration

An illustration of water evaporation through the POF‐based materials. (Credit: Zijing Xia et al)

The ability of POFs to grow on many types of materials makes them easily adaptable for use with locally available materials. This versatility, coupled with the easy, one-step fabrication process, could make the method practical for large-scale production.

The POF-based approach proved highly effective in a lab setting, and the research team plans to conduct further experiments outside the lab to observe the practical performance of POFs.

So far, the research suggests POFs could help drive the sustainable water purification systems of the future.

“POF-based interface engineering design shows promise for large-scale purification methods, and it could also be used for desalination, wastewater treatment and beyond,” Xia said.

Other authors of the paper include PME graduate students Ruben Z. Waldman and Chao Zhang, PME professor and Argonne scientist Shrayesh Patel, and Argonne scientist and PME fellow Seth Darling. Additional authors include Zhaowei Chen of Argonne, Hao-Cheng Yang of Sun Yat-sen University and Yusen Zhao of UCLA.

Citation: “Porphyrin Covalent Organic Framework (POF)-Based Interface Engineering for Solar Steam Generation.” Zijing Xia et al. Advanced Materials Interfaces. Doi: 10.1002/admi.201900254

Funding: The Advanced Materials for Energy-Water Systems (AMEWS) Center

Materials provided by the University of Chicago

The Bukobot Reprap 3D Printer

Graphene based ink that could be used for printing energy storage devices

Scientists have developed an ink based on graphene nanosheets and also demonstrated that this ink can be used for printing 3D structures. This ink based on graphene can be produced on a large scale at very low costs in an eco-friendly manner. This can result in the wide-scale development of a large variety of printable energy storage equipment.

The group of researchers led by Jingyu Sun and Zhongfan Liu from Soochow University and  Beijing Graphene Institute respectively have published a study on their work in ACS Nano journal.

Sun said that their work makes use of the green synthesis of graphene nanosheets that are nitrogen-doped on a salt template with the help of chemical vapour deposition. This gives the room for exploring derived inks in the field of printable energy storage in a greater way.

A major goal in the research of graphene is to make the production of graphene possible at a wide scale assuring both high quality and affordable costs. The production methods used so far resulted in a low quality of graphene with a high number of structural defects and chemical based impurities. Thus it has not been possible to prepare good quality graphene inks.

In this new technique, researchers have used NaCl crystals for growing nitrogen-doped graphene nanosheets with the help of chemical vapour deposition technique as a result of which nitrogen and carbon molecules diffuse on the surface of NaCl crystals. NaCl was chosen due to its wide availability, low cost and high water solubility. For removing sodium chloride, the coated crystals are dipped in water as a result of which NaCl dissolves leaving behind the very pure nitrogen-doped graphene cages. The last step involves giving treatment to the cages with ultrasound as a result of which they transform to two-dimensional nanosheets that are nearly 5-7 layers of graphite in thickness.

These nanosheets have very fewer defects and they are of the perfect size for printing as they are of 5 micrometres in length, whereas the bigger flakes block the nozzle. For putting to test, the actual effectiveness of the ink, a large number of 3D structures were built using the inks. Scientists used the ink as a conductive additive for electrode and then used the composite ink for printing flexible electrodes to be used in supercapacitors with a large power density.

Additionally, scientists also used the ink for printing interlayers for the Li-S batteries. These batteries showed better-enhanced performance with increased conductivity.

network periodic table

Mathematicians propose an alternate way of arranging the elements of periodic table

A periodic table is a very convenient way of arranging the elements which occur in nature. Elements are stored in boxes next to each other and it helps in cataloguing our universe quite efficiently. However, it might not be the only method in which the elements can be arranged or even the best way of arrangement.

Many designs of the periodic table have been provided before and now mathematicians from Max Planck Institute have provided elaborate mathematical techniques for arranging the elements with the help of complex hypergraphs rather than the basic way which is currently used worldwide. Through this method, researchers claim that periodic elements can be adapted in several ways and thus giving many kinds of interpretations in which elements are classified based on the ordering, where every single one of them is correct. The study has been published in the Proceedings of Royal Society journal

The periodic table used presently was devised by a Russian scientist named Dmitri Mendeleev in the year 1869. Based on the 63 elements which were known at that time, he put forward a technique of arranging them. Currently, elements are sorted on the basis of the atomic number, which means the number of protons that occur in the nucleus of an atom.

Along with the atomic number of the element, the atomic weight, the element’s atomic symbol and a colour subgrouping it with other elements of similar properties are also provided. However, in the case of many arrangements, scientists have different opinions on where they are located in the periodic table. The researchers claim that through this hypergraph technique elements can be arranged in several flexible configurations. When arranged on the basis of atomic number within the hypergraph, elements can still be classified in many ways within the organised hypergraph such as water solubility, geological deposits where elements are found etc.

This system, based on chemical bonds, rearranges the elements in a new way. Some elements remain grouped together, such as halogens, because they bond the same way; but others are separated, like silicon and carbon, which, when bonded, form very different compounds.

Mathematician Guillermo Restrepo has compared this solution provided by the team to a sculpture. The shadow cast depends on the direction of light. He said that the periodic tables are the different shadows which are cast. Because of which, there are so many different ways for creating the tables.

Below is the proposed periodic table which is 90 degrees rotated version of the above image

network periodic table

A periodic table of chemical bonds: Each of the 94 circles with chemical element symbols represents the bond that the respective element forms with an organic residue. The bonds are ordered according to how strongly they are polarized. Where there is a direct arrow connection, the order is clear: Bonds of hydrogen, for example, are more polarized than bonds of boron, phosphorus, and palladium. The same applies to rubidium in comparison to caesium, which has particularly low polarized bonds and is therefore at the bottom of the new periodic table. If there is no direct arrow between two elements, they may still be comparable – if there is a chain of arrows between them. For example, the bonds of oxygen are more polarized than the bonds of bromine. Bonds represented by the same colour have the same binding behaviour and belong to one of the 44 classes. Credit: Guillermo Restrepo, MPI for Mathematics in the Sciences

There are three defined conditions for establishing the periodic table. Firstly, it has to be ordered which means the elements have to be catalogued. Second, the arrangement has to be according to a certain property, like the atomic number and the final condition is that there needs to be a criterion for grouping such as chemical similarity. Restrepo said that if the above conditions are satisfied then periodic tables can be created for many other chemical entities and even for elements outside chemistry.

Paper sensor

A paper sensor detects food spoilage

Worldwide, nearly a third of all food is wasted. Much of it is still safe to eat, but consumers throw it away because it’s close to or beyond its printed expiration date. That waste could be mitigated if food were packaged with a sensor that monitored its spoilage in real time. But such a device would need to be low cost, easy to produce, and unambiguous to read. Toward that end, Firat Güder of Imperial College London in the UK and his colleagues have designed a paper sensor that detects the gases emitted during food decomposition.

At typical levels of humidity, a paper surface becomes coated with a thin layer of water, which absorbs water-soluble gases from the environment (right panel of the figure). The gas molecules contribute positive and negative ions that change the water’s electrical conductivity by an amount proportional to the gases’ concentration. To access that electrical information, Güder and his team drew electrodes on paper (left panel) with commercial carbon ink and a ballpoint pen. The device’s conductivity was sensitive to the concentration of ammonia and trimethylamine (TMA), two water-soluble gases associated with food spoilage.

Güder and his colleagues used the sensor to monitor the spoilage of a chicken breast and codfish at room temperature and codfish in the fridge. As the meats decomposed, they produced ammonia, TMA, and dimethylamine, and the sensor’s response increased by up to a factor of 10.

The team integrated the paper sensor into a commercial near-field-communication tag so it could talk to a smartphone. Below a threshold amount of ammonia, the sensor responded to the smartphone; above the threshold, the tag was unresponsive. In a practical application of the sensor, a manufacturer would set the threshold to an appropriate concentration for the product, and the consumer would check the freshness with their phone.

The sensor does have a couple of drawbacks. Its response depends strongly on humidity and doesn’t distinguish among species of water-soluble gases. But the humidity is stable in some environments, such as packaged food, or can be monitored separately, and chemical additives are able to tune water’s sensitivity for specific gases. (G. Barandun et al., ACS Sens., 2019, doi:10.1021/acssensors.9b00555; thumbnail photo credit: Lance Cheung/USDA.

Materials provided by American Institute of Physics

plastic wastes ocean

Researchers successfully convert plastic waste to jet fuel

A group of researchers at Washington State University has found a technique for converting the plastic waste products which are generated every day to jet fuel. Hanwu Lei of WSU and his colleagues have been successful in melting plastic waste at a very high temperature with the help of activated carbon, which is a processed carbon with a greater surface area to form jet fuel. The study has been published in the journal Applied Energy.

Lei, an associate professor at Department of Biological System Engineering in WSU commented that waste plastic is a major problem worldwide. But they have been able to recycle the plastic in a very simple way.

For the experiment, several low-density polythenes and a variety of waste plastic products such as water bottles, plastic bags were tested by the research group and they were ground to a very small size, around the range of three millimetres which is equal to the size of a rice grain. The granules of plastic were then kept above activated carbon, placed in a tube reactor at very high temperature, in the range of 430 to 571 degrees Celsius, which translates to 806 to 1060 Fahrenheit. The activated carbon plays the role of a catalyst which is a substance for increasing the rate of a chemical reaction without itself being consumed in it.

Lei remarked that since plastic is very difficult to be decomposed to smaller particles, the help of a catalyst has to be taken in order to break the chemical bonds. Plastics contain a very high amount of hydrogen, which is an important component in fuels.

Once the carbon catalyst has been used for one set of conversion, it can be again separated and reused for the next batch of conversion of plastics. If the catalyst loses its activity, it can be also be regenerated. Researchers tested several combinations of plastics and the best result obtained was a mixture of 85 per cent jet fuel and 15 per cent diesel fuel.

According to the estimates of Environmental Protection Agency, landfills located in the United States received close to 26 million tonnes of plastic in the year 2015. This is the most recent statistics which are available currently. Scientists estimate that at least 4.8 million tonnes of plastic enter the oceans in the world.

This new technique would help in making the best use of plastic and hence minimize its wastage. Lei said that almost 100 percent of the energy can be recovered from the plastic which is tested. The fuel which is obtained is of decent quality and the byproduct gases are of good quality as well. This process is even highly scalable.

Hope Diamonds

Ocean floor sediments recycle to form salty diamonds

As per the reports of a new study by a team of geoscientists from Macquarie University, Sydney, salt traces trapped in many diamonds reveal on analysis that the stones are produced from the seabeds which have been trapped inside the Earth’s crust for countless years.

A majority of the diamonds which are found on the surface of the Earth are formed in this manner while the others are formed due to the melt crystallisation quite deep in Earth’s mantle. In the experiments, researchers from Goethe Universität and Johannes Gutenberg Universität of Germany simulated the high pressures and temperatures which exist 200 kilometres deep inside the Earth. They found that the seawater which is present in the sediment at the ocean’s bottom reacts in the right way to form the salts which are present in the diamonds.

The study has been published in the journal Science Advances and it clears a major confusion about the way diamonds are formed. It was earlier thought that the salts within diamonds originated from the marine seawater. However, the research cleared that they originated from the marine sediment.

Diamonds are classified into gem diamonds and fibrous diamonds. Gem diamonds are fully composed of carbon in its purest form while fibrous diamonds contain the traces of elements such as sodium, potassium which can disclose a lot of information about the conditions in which their formation took place. Fibrous diamonds normally grow faster than gem diamonds which indicates that small samples of fluids are trapped during formation.

Samples of marine sediment were placed inside a vessel containing a rock called peridotite. It is the most common type of rock which is present in the mantle where diamonds are formed. Pressure and heat were increased and the adequate time to react with one another was given matching the conditions of the mantle.

At values of pressure lying between four and six gigapascals and temperatures in the range of 800 degrees to 1100 degree Celsius, which is equivalent to the depth of 120-180 kilometres inside Earth, salts were produced having the balance of sodium and potassium. It matched with the traces that are obtained inside diamonds.

Dr Michael Förster, lead author of the paper remarked that they have successfully demonstrated the sequence of steps which lead to the growth of diamonds and confirmed that the recycling of sediments in the ocean is responsible for it.


5CB Liquid Crystal

Scientists manufacture on demand designer atoms

In the near future, scientists may be able to create customised atoms as per one’s requirements with only a button’s click. It may sound like science fiction now but a team of researchers at the University of Colorado Boulder reported that they are slowly approaching the possibility of controlling and assembling particles known as “big atoms”.

The research has been published in the Nature journal. It is centred around the colloidal particles which after mixing with liquid crystals behave similar to the elements in the periodic table. These particles give researchers the ability to study the interaction of atoms like hydrogen, helium without having to zoom down to the level of atoms. Scientists demonstrated that for big atoms they could alter their charges with the help of only a switch. It means that particles which were earlier attracted to each other will now repel each other.

Ivan Smalyukh, a physics professor remarked that by having a vast amount of control, scientists can decide on how the particles assemble and which properties they possess. Essentially, it acts like a designer’s toolkit. This toolkit is initiated with a simple material, liquid crystals.

These elements are the ones responsible for brilliant images on our mobile, television screens and are composed of molecules such as rods which all point in one direction. However, in the past decade, researchers observed that if particles like microscopic silica grains are dropped in the liquid crystals, the ordered particles will get altered to make space for the newly added particles.

The remarkable thing is that the bending of the liquid crystals is analogous to the structures possessed by the electron shells in the atoms. The way the liquid crystals bend around the newly added element is very important as when an existent order is disturbed, additional energy is needed to make new arrangements. The problem which scientists faced till now is that they had very less control on the interactions of the big atoms.

Smalyukh’s team used silica in the shape of a hexagon, coated them with a dye which rotates on being exposed to various light types and then added to the liquid crystals. On exposing the mixture to blue light, the molecules would bend in a specific pattern, while it would behave differently on using a different light. The best thing is that no sophisticated laser is needed for these interactions. A normal lamp with a filter is sufficient for it. Which means a bright sunny day is enough for observing the various interactions.

Researchers are quite excited to manipulate these particles by tweaking them in new ways for creating structures not existing in nature and dissolving them similarly.

schematic model of boron

Combination of experiments and calculations allows examination of boron’s complicated dance

In a study that combines experimental work and theoretical calculations made possible by supercomputers, scientists have determined the nuclear geometry of two isotopes of boron. The result could help open a path to precise calculations of the structure of other nuclei that scientists could experimentally validate.

Researchers at the U.S. Department of Energy’s (DOE) Argonne National Laboratory, in collaboration with scientists in Germany and Poland, determined the difference in a quantity known as the nuclear charge radius between boron-10 and boron-11. The nuclear charge radius indicates the size of an atomic nucleus — which often has relatively indistinct edges.

This is one of the most complicated atomic nuclei for which it is possible to arrive at these precise measurements experimentally and derive them theoretically.” — Argonne nuclear physicist Peter Mueller

Nuclear charge radii are difficult to compute with high precision for atoms much larger than boron because of the sheer number of neutrons and protons whose properties and interactions must be derived from quantum mechanics.

The nuclear theory builds from quantum chromodynamics (QCD), a set of physical rules that apply to quarks and gluons that compose the protons and neutrons within the nucleus. But trying to solve the nuclear dynamics using QCD alone would be an almost impossible task due to its complexity, and researchers have to rely on at least some simplifying assumptions.

Because boron is relatively light — with only five protons and a handful of neutrons — the team was able to successfully model the two boron isotopes on the Mira supercomputer and study them experimentally using laser spectroscopy. Mira is part of the Argonne Leadership Computing Facility (ALCF), a DOE Office of Science User Facility.

This is one of the most complicated atomic nuclei for which it is possible to arrive at these precise measurements experimentally and derive them theoretically,” said Argonne nuclear physicist Peter Mueller, who helped lead the study.

Looking at how the nuclear configurations of boron-11 (11B) and boron-10 (10B) differed involved making determinations at extraordinarily small length scales: less than a femtometer — one-quadrillionth of a meter. In a counterintuitive finding, the researchers determined that the 11nucleons in boron-11 actually occupy a smaller volume than the 10 nucleons in boron-10.

To look experimentally at the boron isotopes, scientists at the University of Darmstadt performed laser spectroscopy on samples of the isotopes, which fluoresce at different frequencies. While most of the difference in the fluorescence patterns is caused by the difference in the mass between the isotopes, there is a component in the measurement that reflects the size of the nucleus, explained Argonne physicist Robert Wiringa.

To separate these components, collaborators from the University of Warsaw and Adam Mickiewicz University in Poznan carried out state-of-the-art atomic theory calculations that precisely describe the complicated dance of the five electrons around the nucleus in the boron atom.

Earlier electron scattering experiments couldn’t really say for sure which was bigger,” Wiringa said. ​By using this laser spectroscopy technique, we’re able to see for certain how the extra neutron binds boron-11 more closely.”

The good agreement between experiment and theory for the dimensions of the nucleus allows researchers to determine other properties of an isotope, such as its beta decay rate, with higher confidence. ​The ability to perform calculations and do experiments go hand-in-hand to validate and reinforce our findings,” Mueller said.

The next stage of the research will likely involve the study of boron-8, which is unstable and only has a half-life of about a second before it decays. Because there are fewer neutrons in the nucleus, it is much less tightly bound than its stable neighbors and is believed to have an extended charge radius, Mueller said. ​There is a prediction, but only experiment will tell us how well it actually models this loosely bound system,” he explained.

An article based on the research, ​Nuclear Charge Radii of 10,11B,” appears in the May 10 issue of Physical Review Letters. In addition to Argonne’s Alessandro Lovato, researchers from two German and two Polish universities also collaborated.

Materials provided by Argonne National Laboratory