October 19th, 2006 23:31 EST
U.S. Energy Department, Russian Scientists Discover Element 118
New element in periodic table provides insight into the makeup of the universe
In experiments conducted at JINR between February and June 2005, the researchers used a particle accelerator to bombard the synthetic element californium with billions and billions of charged calcium atoms, called calcium ions.
The result was ununoctium, the temporary name for a “superheavy” element that is expected to be a gas like xenon, krypton or radon when its chemical properties are finally studied. It would lie just below radon on the periodic table of elements.
“We put 1019 calcium ions – that’s a one followed by 19 zeros [10,000,000,000,000,000,000] – through this target over the span of three months,” Livermore team leader Ken Moody told the Washington File October 17, “and made three atoms of element 118.”
Moody added, “Anything we can learn about the building blocks that put the world together has to be an important discovery, and finding out the ultimate number [of elements] that can possibly exist is sort of the goal.”
ATOMS AND ELEMENTS
An element is a substance that cannot be broken down into a simpler substance by ordinary chemistry -- heat, light, acids -- and every material thing in world is made up of combinations of about 90 elements.
Atoms, the smallest units of matter that have all the characteristics of an element, contain three main "subatomic" particles -- protons, neutrons and electrons. Protons and neutrons exist in an atom's center, called the nucleus. Lightweight electrons exist in a cloud that surrounds the nucleus. Each atom's weight equals its protons plus its neutrons.
The periodic table lists elements horizontally in order of their atomic number (number of protons in the nucleus), and vertically in order of the number of electrons around the nucleus.
The heaviest element found in nature in sizeable quantities is uranium, which in its most common form contains 92 protons and 146 neutrons. Superheavy elements like 118, also called transuranic elements, are heavier than uranium and do not exist in nature -- they can be created only in nuclear reactors or particle accelerators. (See related article.)
The more protons and neutrons there are in a nucleus of an atom, the less stable the atom, so superheavy elements usually exist only for tiny fractions of seconds. That was the prevailing theory until the 1960s, when nuclear physicists predicted the existence of something called the “island of stability.”
This concept introduced the possibility that certain elements could have particularly stable “magic numbers” of protons and neutrons and, unlike other superheavy elements, would be much more stable and slower to decay.
The magic number, they said, would begin with element 114, which would have 114 protons and 184 neutrons.
“The island is just an area where the nuclei are extra stable,” Moody explained, “because of these quantum mechanical rules that give neutrons and protons more binding energy and [the energy] helps hold the nucleus together and resist fission” -- the splitting apart of the nucleus.
Quantum mechanics is a physical science dealing with the behavior of matter and waves on the scale of atoms and subatomic particles.
THE ISLAND OF STABILITY
The Livermore-Dubna team, in a 1998 experiment, made nuclei with 114 protons but nothing approaching 184 neutrons.
When the researchers created element 114, they expected the atoms to have half-lives (the time it takes for half the atoms in a sample to decay) of microseconds, or even nanoseconds, but the atoms had half-lives of several seconds.
“That maybe doesn’t sound like much to the layperson,” Moody said, “but it was an absolutely astounding finding for us.”
In later years, attempting to create nuclei with 184 neutrons, they produced elements 115, 116 and now 118.
“Every time we do that, we get farther from the proton number and lose ground, but we get closer to the neutron number and gain ground,” Moody said.
“What you could say is that we’re sort of exploring the shore of this island of extra stability that has peaked out and we can’t actually get to the peak,” Moody said. “I don’t know if our feet are dry or wet, but we’re in the sand on the beach and we can certainly see that something very interesting is going on, but we haven’t reached the center of the effect.”
To reach the center, he added, may take the next great leap in technology. In 2007, the team plans to attempt creation of element 120 by bombarding a plutonium target with iron isotopes.
“We’re getting close to the edge, we’re at the precipice and we’re looking out and trying to find out where the edge is where nothing can exist anymore,” Moody said. “It’s kind of exciting to be close after all these years.”
Additional information about element 118 is available at the DOE Lawrence Livermore National Laboratory Web site.