From NSLC at Michigan State University: “Double Trouble: First Sighting of 2p Decay Between IAS Isotopes” 

“A few months ago, Bob Charity, Lee Sobotka and a team of researchers saw something at NSCL that nobody had ever seen before. The nuclear physicists from Washington University in St. Louis detected a new twist on a very rare form of nuclear decay – the emission of two protons in a single step between excited states of a very peculiar sort: isobaric-analog states or IAS.

One of the many fundamental processes that researchers attempt to understand by conducting experiments at NSCL is nuclear decay. When a nucleus is unstable, it will decay by shedding energy in the form of expelling particles like protons and neutrons or bits of energy like gamma rays or photons. Some isotopes like carbon-14 can take thousands of years to decay while others last tiny fractions of a second.

Because these latter types exist for but a fleeting instant, they can only be found in nature in the places where they are made like stars, supernova, neutron stars and other astronomical phenomena. This is how the heavy elements are formed. Exploding stars pump so much energy into the particles that they form exotic nuclei that quickly decay into the stable elements we see every day.”

Quantum numbers are used to describe the energy and angular momentum of every particle in an atom. An isobaric-analog state is an excited state of a nucleus that has the exact same structure – or set of quantum numbers – as the ground state of another except, for example, one proton has become a neutron. In the figure above, the ground state of carbon-8 and the isobaric analog state in boron-8 have the exact same arrows in the exact same places pointing the exact same directions, but one red arrow (proton) in carbon-8 (top left) has become a blue arrow (neutron) in boron-8 IAS (top right). The “IAS” notation is necessary because this structure is an excited state in boron-8. In the ground state (bottom right) – or the state of lowest energy – one of the protons has an opposite spin, denoted by the red arrow pointing in the opposite direction.

Bob Charity (professor at WU) and Bec Shane (graduate student at WU).

See the full article here.