The Chemistry of Superheavy Elements

Experiments with superheavy elements

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This isotope, lawrencium, displayed a half-life of 11 hours, which is extraordinarily long for an atom of such a heavy element. Previously known isotopes of lawrencium had fewer neutrons and were much less stable. Lawrencium has protons and neutrons, hinting at as-yet-undiscovered magic numbers that may be used to form new elements. Which configurations might possess magic numbers?

The answer depends who you ask, because it's a matter of calculation and there's not standard set of equations. Some scientists suggest there might be an island of stability around , , or protons and neutrons. Others suggest a spherical nucleus with neutrons, but , , or protons might work best.

Unbihexium element is "doubly magic" because its proton number and neutron number are both magic number. However you roll the magic dice, data obtained from the synthesis of elements , , and point toward increasing half-life as the neutron number approached Some researchers believe the best island of stability might exists at much larger atomic numbers, like around element number protons.

Although scientists might be able to form new stable isotopes of known elements, we don't have the technology to go much past work which is currently underway. It's likely a new particle accelerator will need to be constructed that would be capable of focusing onto a target with greater energy.

Maximum production rates are on the order of a few atoms per day at most, and are even less for the heavier ones. Second, the atoms decay quickly through radioactive processes — in the present case within about 10 seconds, adding to the experiment's complexity. A strong motivation for such demanding studies is that the very many positively charged protons inside the atomic nuclei accelerate electrons in the atom's shells to very high velocities — about 80 percent of the speed of light.

According to Einstein's theory of relativity, the electrons become heavier than they are at rest. Consequently, their orbits may differ from those of corresponding electrons in lighter elements, where the electrons are much slower. Such effects are expected to be best seen by comparing properties of so-called homologue elements, which have a similar structure in their electronic shell and stand in the same group in the periodic table.

This way, fundamental underpinnings of the periodic table of the elements — the standard elemental ordering scheme for chemists all around the world — can be probed. Chemical studies with superheavy elements often focus on compounds, which are gaseous already at comparatively low temperatures.

This allows their rapid transport in the gas phase, benefitting a fast process as needed in light of the short lifetimes. To date, compounds containing halogens and oxygen have often been selected; as an example, seaborgium was studied previously in a compound with two chlorine and two oxygen atoms — a very stable compound with high volatility. However, in such compounds, all of the outermost electrons are occupied in covalent chemical bonds, which may mask relativistic effects.

The search for more advanced systems, involving compounds with different bonding properties that exhibit effects of relativity more clearly, continued for many years. Initial tests were carried out at the TRIGA Mainz research reactor and were shown to work exceptionally well with short-lived atoms of molybdenum. Alexander Yakushev from the GSI team explains: "A big challenge in such experiments is the intense accelerator beam, which destroys even moderately stable chemical compounds.

Exploring the superheavy elements at the end of the periodic table

To overcome this problem, we first sent tungsten, the heavier neighbor of molybdenum, through a magnetic separator and separated it from the beam. Chemical experiments were then performed behind the separator, where conditions are ideal to study also new compound classes. Theoretical studies starting in the s predicted these to be rather stable. Seaborgium is bound to six carbon monoxide molecules through metal-carbon bonds, in a way typical of organometallic compounds, many of which exhibit the desired electronic bond situation the superheavy element chemists were dreaming of for long.

Hiromitsu Haba, team leader at RIKEN, explains: "In the conventional technique for producing superheavy elements, large amounts of byproducts often disturb the detection of single atoms of superheavy elements such as seaborgium. Using the GARIS separator, we were able at last to catch the signals of seaborgium and evaluate its production rates and decay properties. In , the two groups teamed up, together with colleagues from Switzerland, Japan, the United States, and China, to study whether they could synthesize a superheavy element compound like seaborgium hexacarbonyl.

In two weeks of round-the-clock experiments, with the German chemistry setup coupled to the Japanese GARIS separator, 18 seaborgium atoms were detected. The gaseous properties as well as the adsorption on a silicon dioxide surface were studied and found to be similar to those of the corresponding hexacarbonyls of the homologs molybdenum and tungsten — very characteristic compounds of the group-6 elements in the periodic table — adding proof to the identity of the seaborgium hexacarbonyl.

The measured properties were in agreement with theoretical calculations, in which the effects of relativity were included. Hideto En'yo, the director of RNC says: "This breakthrough experiment could not have succeeded without the powerful and tight collaboration between fourteen institutes around the world.

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Frank Maas, the director of the HIM, says "The experiment represents a milestone in chemical studies of superheavy elements, showing that many advanced compounds are within reach of experimental investigation. The perspectives that this opens up for gaining more insight into the nature of chemical bonds, not only in superheavy elements, are fascinating. Following this first successful step along the path to more detailed studies of the superheavy elements, the team already has plans for further studies of yet other compounds, and with even heavier elements than seaborgium.

Soon, Einstein may have to show the deck in his hand with which he twists the chemical properties of elements at the end of the periodic table.

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Explore further. More from Atomic and Condensed Matter.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more. Slamming neon element 10 into uranium, for example, yields nobelium But the odds of fusion and survival decrease markedly as atoms grow heavier because of increased repulsion between the positively charged nuclei, among other factors. Creating most elements in the superheavy realm beyond therefore requires special tricks.

Oganessian developed one in the s: cold fusion. Unrelated to the notorious nuclear power work of the s, Oganessian's cold fusion involves uniting beam and target atoms that are more similar in size than those in traditional elementmaking. Doing that is harder than it sounds because the beam and target nuclei are both positively charged and therefore repel each other. Incoming atoms need enough speed to overcome that repulsion, but not so much that they blow the resulting superheavy nucleus apart.

Compared with previous accelerators, the SHEF has a more intense beam, which is accelerated to roughly one-tenth the speed of light in a tight space. But the method ran into limitations as the odds of fusion and survival dropped precipitously. Starting in , a team at the RIKEN Institute in Wako, Japan, tried to use cold fusion to create element , firing zinc element 30 onto bismuth They got one atom the next year and another in , which they celebrated in their control room with cheers, beers, and sake.

Then, the agony started. Needing one more atom to confirm the discovery, the RIKEN team reran the experiment in and None appeared. They tried again in and Not until —7 years later— did they detect another. Getting beyond required a different approach, hot fusion, which Flerov scientists had developed in the late s. Hot fusion uses higher beam energies and relies on a special isotope with a large excess of neutrons, calcium Neutrons stabilize a superheavy atom by diluting the repulsive force of protons, which would otherwise tear the nucleus apart.

But the investment paid off. RIKEN sweated for 9 years to find three atoms of Dubna snagged that many atoms of within 6 months, a discovery Oganessian and colleagues celebrated in their control room with cheers, beers, and shots of spirits.

Transuranium element - Wikipedia

At that point, producing the next few superheavies was largely arithmetic. Calcium is element 20, and calcium plus americium element 95 yielded element Calcium plus curium 96 yielded element , and so on. After , however, things stalled again. Fusion requires several milligrams of the target element, and producing enough einsteinium element 99 to make element is impossible with today's technology. Some researchers proposed replacing calcium with titanium, which has two more protons, and then firing it at elements 97 and 98 to produce and , respectively. But for technical reasons, the likelihood of fusion is just one-twentieth as high with titanium as with calcium.

For most accelerators, that drops the odds of success into the realm of RIKEN's experiments to create —God's statistics all over again. The SHEF was built to overcome those obstacles. In contrast to the grease monkey feel of the older Flerov accelerators, the SHEF is pristine: Bubble wrap still covers the door handles, and for now the floors are spotless. An office at the Flerov Laboratory of Nuclear Reactions in Dubna, Russia, preserves decades-old instruments—and an outdated periodic table. Overall, the SHEF is a fusion of the brawny and the delicate.

The beam originates in an ion source and accelerator that stands two stories high, bigger than some dachas in town. The ion source fires off 6 trillion atoms per second, 10 to 20 times as many as other elementmaking accelerators. The cyclotron's ton magnet was fabricated in in Kramatorsk, Ukraine, near the front line of the recent war with Russia, says Alexander Karpov, a Flerov physicist. The city endured heavy shelling and other military action then, and Karpov says lab personnel were nervous that the magnet would be damaged or destroyed.

After accelerating the beam to roughly one-tenth the speed of light, the cyclotron directs it toward the delicate part of the operation: micrometer-thin metallic foils with target atoms plated onto them. Those foils are mounted onto a disk roughly the size of a CD, which spins to keep cool. If it didn't, the beam would fry a hole in it. If fusion occurs, the resulting superheavy atom sails through the foil. Unfortunately, the foil is so thin that gobs of other particles slip through as well, producing a blizzard of extraneous noise.

That's when the separator comes into play. It consists of five magnets painted the same bright red as a fire truck and collectively weighing twice as much as one—64 tons. Despite the bulk, the magnets are aligned to within 0. The separator, like the beam source, gives the SHEF an advantage. Earlier separators were tuned to superheavy atoms with a narrow range of speed, charge, and direction; those that deviated too much ended up in the beam dump.

The new separator is more generous, giving a pass to two to three times as many superheavy atoms. After slaloming through the separator, an atom arrives at a silicon-germanium detector, which records the atom's position and time of arrival and then starts to monitor it.

Superheavy atoms decay by emitting a series of alpha particles—bundles of two protons and two neutrons. Releasing an alpha changes the atom's identity: element becomes , which becomes , and so on. That decay chain is what allows scientists to identify, retroactively, which element they've created.

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Each alpha particle in the chain flies off with a characteristic energy. So if the detector spots an alpha with the right energy—and, crucially, sees that it emerged from the same point on the detector where a superheavy atom just landed—it begins to watch closely for more alphas. To aid that search, the detector automatically shuts off the cyclotron beam to reduce the amount of cruft flying around. The shutdown also triggers a loud beep in the SHEF's control room, where a few probably bored scientists will be sitting.

On a recent visit to another control room here, two graduate students were watching a schlocky sci-fi monster flick. The bell is a moment of excitement amid the monotony.

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