lifetıme Secret of a
How long a neutron lives
holds clues to the cosmos
By Rebecca Cheung
In the nuclear family, the neutron is clearly the black sheep. Unlike its sibling the proton, the neutron is eccentrically — and irritatingly — neutral. Because they have
no electrical charge, neutrons are hard
to guide and focus using electric fields.
And unlike protons, which can be liberated by igniting hydrogen gas, the neutron is stubbornly sequestered within
the atomic nucleus, making it especially
hard to interact with one-on-one.
When a neutron “dies,” it decays into a
proton. An electron and an antineutrino
are emitted in the process.
says Geoffrey Greene, a physicist at the
University of Tennessee, Knoxville and
Oak Ridge National Laboratory who has
been working on determining the neutron’s lifetime for three decades.
Right now, teams with two very different approaches — one working with
beams of neutrons and another that uses
bottles to trap them — are t weaking their
experiments in hopes of determining
this elusive property.
Dying to know
Neutrons are usually bound in a nucleus,
where they can stay as long as the nucleus
remains intact. But neutrons free from
nuclear confinement are unstable: The
weak nuclear force compels them to
break apart and die.
At the end of its life, a neutron turns
into a proton, a process known as beta
decay. When the proton appears, two
more particles fly away: the small, neg-
atively charged electron (the beta par-
ticle) and a ghostlike particle known as
an antineutrino. This decay process is the
same one that occurs when carbon- 14, the
radioactive isotope used in carbon dating,
decays into the stable nitrogen- 14.
