Scientists observe nucleus decay into four particles

What we know about beta decay

Nuclear scientists have previously observed multiple types of nuclear decay. One such process is beta-plus decay, where a proton turns into a neutron and emits energy in the form of a positron and an antineutrino.

A positron is an antimatter version of an electron, while the antineutrino is the antimatter counterpart of a neutrino.

After the initial decay, the resulting nucleus can have enough extra energy to lead to an emission of a few more particles, helping it reach a more stable state. This additional decay was observed for the first time by the researchers at Texas A&M University.

The experiment

The research team used the cyclotron at the university to produce a beam of radioactive nuclei at high energies. The Cyclotron is another name for a particle accelerator and was used to accelerate nuclei to speeds matching 10 percent that of light.

For their experiment, the team used oxygen-13, an isotope of oxygen with eight protons and five neutrons, and sent it at accelerated speeds inside the Texas Active Target Time Projection Chamber (TexAT TPC).

The chamber of the TexAT TPC is filled with carbon dioxide, which stops the accelerated beam of oxygen-13. Ten milliseconds after entering the chamber, oxygen-13 decays by emitting a positron and a neutrino.

Since the researchers were able to deliver molecules of oxygen-13, one nucleus at a time, into the detector, they were able to observe its decay and measure any particles that boiled off following the beta decay. They analyzed the data with a computer program to identify particles in the gas.

The team observed that the nucleus split into three helium nuclei without any electrons revolving around them: a proton and a positron. It was the very first time this type of observation was made. It was difficult to observe since such decay is relatively rare and occurs only once every 1,200 decays.

The findings from the experiment can help researchers learn more about the decay process and properties of the nucleus prior to the decay.

The research findings were published in the journal Physical Review Letters.

Abstract:

The β-delayed proton decay of 13O has previously been studied, but the direct observation of β-delayed 3αp decay has not been reported. Rare 3αp events from the decay of excited states in 13N⋆ provide a sensitive probe of cluster configurations in 13N. To measure the low-energy products following β-delayed 3αp decay, the Texas Active Target (TexAT) time projection chamber was employed using the one-at-a-time β-delayed charged-particle spectroscopy technique at the Cyclotron Institute, Texas A&M University. A total of 1.9×105 13O implantations were made inside the TexAT time projection chamber. A total of 149 3αp events were observed, yielding a β-delayed 3αp branching ratio of 0.078(6)%. Four previously unknown α-decaying excited states were observed in 13N at 11.3, 12.4, 13.1, and 13.7 MeV decaying via the 3α+p channel.