Friday, April 10, 2015

How Do You Solve a Problem Like Lawrencium?

You'd figure an element with a half-life of 27 seconds shouldn't cause that much trouble. But some recent experiments with the heavy radioactive element lawrencium have been giving scientists some furrowed brows as they try to figure out just where the heck it belongs on the well-known periodic table.

Lawrencium -- named after Ernest Lawerence, who invented the cyclotron particle accelerator -- is one of those elements that doesn't appear in nature. That's because of that short half-life issue. "Half-life" is a term that scientists use to describe how long it takes for half of the atoms in any given amount of an element to decay into another element. If you put a pound of plutonium-238 in the cupboard today (which you probably shouldn't), you would open your cupboard door in late 2107 to find half a pound of plutonium-238 and some other stuff. With a half-life of 27 seconds, lawrencium is here today and gone well before tomorrow. These elements have existed in nature but have long since decayed into their other forms.

But by using high-energy particle accelerators and shooting exotic elements at each other, some of these rare atoms can be created long enough to be studied. So we can take a quick look at lawrencium and how it behaves. The experiments described in the Nature story resulted in an ionized form of lawrencium, which is what physicists and chemists call it when an element that still has all its protons and neutrons misplaces an electron somewhere.

The problem is that lawrencium shouldn't have ionized as it did, if it matches the other elements in its area of the periodic table. Rather than just being a random listing of those elements, the periodic table is designed to show relationships among them. Elements in certain columns will react in similar ways in similar experiments, for example, even though they are distinct elements. Some scientists say the results of the lawrencium experiment, which showed it ionizing at a very low energy level, should group it with elements on one side of the periodic table, but others point to reasons why the same experiments ought to group it on another side.

Of course, all the fuss over an element that requires a massively expensive particle accelerator and some other artificially-created elements just to show up for a few seconds would seem to be much ado about nothing. After all, few of us have to retain much knowledge about the periodic table once we've moved on from chemistry class, and those that do always seem to have a great pull-down version at the front of the classroom to which they can refer. But the periodic table was drawn the way it was because of relationships that exist among elements. In other words, the elements produced the format of the chart, not the other way round. So an element that doesn't fit where it might otherwise seem to means there are some things that still need to be figured out about the world.

And that's always interesting news. Or at least it should be.

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