Science News - USA (2021-11-20)

http://www.sciencenews.org | November 20, 2021 21

FROM TOP: FRIB; T. TIBBITTS T. TIBBITTS

Lithium-11 is just one example of what happens

when nuclei get weird. Such nuclei, Nunes says,

“have properties that are mind-blowing.” They

can become distorted into unusual shapes, such as

a pear (SN: 6/15/13, p. 14). Or they can be sheathed

in a skin of neutrons — like a peel on an inedible

nuclear fruit (SN: 6/5/21, p. 5).

A new tool will soon help scientists pluck these

peculiar fruits from the atomic vine. Research-

ers are queuing up to use a particle accelerator at

Michigan State to study some of the rarest atomic

nuclei. When it opens in early 2022, the Facility

for Rare Isotope Beams, or FRIB (pronounced

“eff-rib”), will strip electrons off of atoms to make

ions, rev them up to high speeds and then send

them crashing into a target to make the special

nuclei that scientists want to study.

Experiments at FRIB will probe the

limits of nuclei, examining how many

neutrons can be crammed into a

given nucleus, and studying what

happens when nuclei stray far

from the stable configurations

found in everyday matter. With

FRIB data, scientists aim to piece

together a theory that explains

the properties of all nuclei, even

the oddballs. Another central target:

pinning down the origin story for chemical

elements birthed in the extreme environments of

space.

And if scientists are lucky, new mind-blowing

nuclear enigmas, perhaps even weirder than

lithium-11, will emerge. “We’re going to have a new

look into an unexplored territory,” says nuclear

physicist Brad Sherrill, scientific director of FRIB.

“We think we know what we’ll find, but it’s unlikely

that things are going to be as we expect.”

Exploring instability

Atomic nuclei come in a dizzying number of vari-

eties. Scientists have discovered 118 chemical

elements, distinguished by the number of pro-

tons in their nuclei (SN: 1/19/19, p. 18). Each of

those elements has a variety of isotopes, differ-

ent versions of the element formed by switching

up the number of neutrons inside the nucleus.

Scientists have predicted the existence of about

8,000 isotopes of known elements, but only about

3,300 have made an appearance in detectors.

Researchers expect FRIB will make a sizable dent

in the missing isotopes. It may identify 80 percent

of possible isotopes for all the elements up through

uranium, including many never seen before.

The most familiar nuclei are those of the

roughly 250 isotopes that are stable: They don’t

decay to other types of atoms. The ranks of stable

isotopes include the nitrogen-14 and oxygen-16

in the air we breathe and the carbon-12 found in

all known living things. The number following

the element’s name indicates the total number of

protons and neutrons in the nucleus.

Stable nuclei have just the right combination

of protons and neutrons. Too many or too few

neutrons causes a nucleus to decay, sometimes

slowly over billions of years, other times in mere

fractions of a second (SN: 3/2/19, p. 32). To under-

stand what goes on inside these unstable nuclei,

scientists study them before they decay. In gen-

eral, as the proton-neutron balance gets more

and more off-kilter, a nucleus gets further from

Curious halo

Lithium-11’s nucleus

has a center packed with

protons and neutrons,

surrounded by two

neutrons in a broad halo.

If one of those three

components is removed,

the nucleus can’t stay

bound, what’s known as

a Borromean nucleus.

When it

switches on

in early 2022,

the Facility for

Rare Isotope Beams’

particle accelerator

(shown) will accelerate

beams of ions to about half

the speed of light.

With a new particle accelerator, scientists set their sights on

unexplored atomic territory By Emily Conover

Extreme

NUCLEI

Extreme

IN SEARCH OF

rare-isotope.indd 21rare-isotope.indd 21 11/3/21 11:21 AM11/3/21 11:21 AM