Synopsis: Neutron Capture Constraints

Physics 9, s66
Experiments place tighter bounds on neutron capture rates that play an important role in the production of heavy elements in the Universe.
Alan Stonebraker/APS

Heavy nuclei are typically forged in high-energy astrophysical events where neutrons collide and merge with nuclei. For highly unstable nuclei, researchers cannot directly measure this so-called neutron capture, so they must estimate the capture rates using highly model-dependent theories. A new study uses nuclear decay analysis to tightly constrain the neutron capture rate of the unstable nucleus nickel-69, which is an important stepping stone in building heavier nuclei.

Most elements heavier than iron can only form in a rapid neutron capture process, or r process, in which multiple capture events happen in a matter of seconds. Astrophysicists have proposed several situations where the r process may occur, such as in supernovae and neutron-star mergers. However, determining the output of heavy elements from each of these events will require better estimates of capture rates.

For their neutron capture rate measurement, Sean Liddick from the National Superconducting Cyclotron Laboratory at Michigan State University and his colleagues have used the so-called β-Oslo method, which involves analyzing the 𝛾 rays emitted by a nucleus. This is the first time that this type of analysis has been used to study a relatively light nucleus integral to the r process. The researchers measured the 𝛾 rays emitted by a sample of nickel-70, which is the nucleus that forms when nickel-69 captures a neutron. From these data, the team calculated the neutron capture rate for nickel-69 with an uncertainty 10 times smaller than previous estimates. Inserting this more precise rate into numerical simulations of the r process, the researchers were able to place tighter constraints on the estimated yields of nuclei with atomic mass between 70 and 130.

This research is published in Physical Review Letters.

–Michael Schirber

Michael Schirber is a Corresponding Editor for Physics based in Lyon, France.


Subject Areas

Nuclear Physics

Related Articles

Neutrino Detectors for National Security
Nuclear Physics

Neutrino Detectors for National Security

Detecting neutrinos offers a new way to monitor the potential bomb materials inside a nuclear reactor, but the technology’s practicality remains uncertain. Read More »

Synopsis: Gold Nucleus is Wobbly
Nuclear Physics

Synopsis: Gold Nucleus is Wobbly

A rare kind of nuclear spinning motion has been detected in an isotope of gold. Read More »

Synopsis: Earth As a Neutrino Source
Geophysics

Synopsis: Earth As a Neutrino Source

The Borexino experiment has doubled its data on neutrinos generated inside Earth, providing new constraints on geological models of the mantle. Read More »

More Articles