Despite a new measurement, the neutron’s lifetime is still puzzling

neutron lab experiment

LIFETIME ACHIEVEMENT  To make a new measurement of the neutron’s lifetime, physicists confined neutrons within a chamber and counted the number that remained using an apparatus (shown) located at Los Alamos National Laboratory in New Mexico.

Courtesy Los Alamos National Lab

A genie in a bottle might grant you a wish, but neutrons trapped in a bottle aren’t so accommodating.

Outside of an atomic nucleus, the neutral particles eventually decay into other particles. But scientists aren’t sure exactly how long neutrons stick around for before their demise: Two types of neutron lifetime measurements disagree. One type of estimate, made with a beam of neutrons, finds a lifetime about nine seconds longer than another technique, which involves trapping neutrons in a “bottle” and later counting how many remain.

Now, physicists have made a new, more precise bottle measurement of the neutron’s lifetime, pegging it at 877.7 seconds, or around 14.6 minutes, a team reports online May 6 in Science. Although the new measurement fixes some of the pitfalls of earlier experiments, it still disagrees with the beam experiments.

The impasse is hindering attempts to understand the infant universe, causing problems for calculations of how atomic nuclei formed after the Big Bang. Scientists can’t yet explain the difference, but some have speculated that weird new particles could be to blame.

Physics writer Emily Conover has a Ph.D. in physics from the University of Chicago. She is a two-time winner of the D.C. Science Writers’ Association Newsbrief award.

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