Quest Aims to Create Bigger Atoms and New Kinds of Matter (LiveScience.com)

A quest is underway to create larger and larger atoms with more

protons and neutrons than ever before.

By building these super-heavy elements, scientists are not

just creating new kinds of matter - they are probing the subatomic world and

learning about the mysterious forces that hold atoms together.

"Of course discovering something new is always very

interesting, but the main motivation is, we don't understand how nuclei work

out in these extreme limits," said Dawn Shaughnessy, a chemist at Lawrence

Livermore National Laboratory in Livermore, Calif.

The scientists are also working toward a tantalizing goal:

They hope to discover a theoretical "island of stability" where ultra-large

elements all of a sudden become easier to make. While most extremely heavy

atoms disintegrate in fractions of a second, theory predicts that once

elements reach a magic number of protons and neutrons, they become relatively

stable again. Finding these magic numbers could also provide revealing clues

about how atoms work.

Heaviest one yet

So far, the heaviest element ever created has 118 protons.

The number of protons in an atom - called the atomic number - determines what

kind of element it is. So hydrogen means any atom

with one proton, while oxygen is an atom with eight protons, or atomic number

eight.

Generally, an atom has close to

equal numbers of protons and neutrons, but this isn't always the case. And an

oxygen atom can gain or lose neutrons but remain oxygen, as long as it has

eight protons.

The heaviest element found in

nature - uranium - has 92 protons. Everything heavier is man-made.

Shaughnessy's team, in collaboration with scientists at the

Joint Institute for Nuclear Research (JINR) in Dubna, Russia, discovered five

of the heaviest elements known, including element 118. Their other conquests

include elements 113, 114, 115, and 116.

Some of their latest work indicates they may be creeping

closer to the island of stability. They can tell by measuring how long their

atoms last before decaying, or breaking up into smaller atoms.

Most super-heavy elements last only microseconds or

nanoseconds before decaying; it's hard for atoms with so many protons and

neutrons to hold together. But some jumbo elements, with numbers of protons or

neutrons that are close to the magic numbers, can last seconds or minutes. For

example, early tests of the element 114 suggested it may have a half-life as

long as 30 seconds. A half-life is the time it takes for half of the substance

to decay.

"Even though we're not quite to the region of stability

yet, we see things that can last tens of seconds, close to minutes," Shaughnessy

told LiveScience. "For these kinds of things, a minute is like an eternity."

Finding elements that are relatively long-lived is exciting,

not just because it hints at the island of stability, but because it provides a

better chance for scientists to learn more about the element.

"Once you make a few atoms of something, and if they

live in the few-seconds range, you can do chemistry on it," Shaughnessy

said. "You can discover its fundamental chemical properties."

Smashing atoms

To create their monster elements, the teams use a particle

accelerator called a cyclotron to speed up beams of calcium nuclei to about

10 percent of the speed of light. Then they smash these calcium ions into a

target of stationary atomic nuclei.

For example, to create element 118 the researchers collided

calcium, which has 20 protons, with californium, the element with 98 protons.

Usually, the bombarding particles will just bounce off the target, but once in

a while, two nuclei will stick together and create what's called a composite

nucleus. Since 98 and 20 add up to 118, the resulting fused nucleus was the

element 118.

To find just a handful of the ultra-heavy elements, the

teams had to run their experiments for months.

"In a six-month experiment, we may see three to ten

atoms," Shaughnessy said.

The scientists rig up special detectors primed to look for the

element they're hoping to create. The detectors look for the right energy

signature predicted for their goal element, while using magnets to divert any

other particles.

Both the Lawrence Livermore-JINR team, and a competing

German team, have been searching for element 120, but so far have struck out.

"We both ended up not finding anything, so we think we're

hitting the limit of our current capability," Shaughnessy said. "As

we go higher and higher, the event rate will get even smaller. You either have

to run longer experiments or you have to improve technology sensitivity on how

you detect these things." (The event rate refers to how often the target

element will form.)

Magic numbers

The researchers think they may be honing in on the fabled

magic numbers that create stable atoms.

Element 114 lasted longer than any of the super-heavy

elements just below it with fewer protons. Element 116 also had a relatively

long half-life, but then element 118 turned out to be less stable, lasting less

than a millisecond before decaying.

This tells the researchers they might be getting close -

especially to the magic number of protons. The magic number of neutrons is

still thought to be a ways off.

"The question is how far away are we seeing the effect?"

Shaughnessy said. "We know we're not at the island of stability, but we

are seeing longer half-lives."

The numbers of particles that can easily pack into an atom's

nucleus is thought to depend on the complex arrangement of both protons

and neutrons within the nucleus.

Just as electrons in an atom have energy states, protons and

neutrons also have energy levels. Each energy level can hold a certain number

of protons or neutrons; when a nucleus' highest energy levels are full, the

particle is stable.

Scientists think the magic numbers are the numbers of

protons and neutrons that completely fill a set of energy levels. An atom in

this configuration would feel relatively secure, and wouldn't want to lose any

protons or neutrons to decay into a smaller atom.

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