Not all matter around us is stable. Some substances undergo radioactive decay to form more stable isotopes. Using advanced equipment at the Texas A&M University Cyclotron Institute, scientists have observed for the first time a unique radioactive decay of oxygen-13, producing three helium nuclei, a proton and a positron.
Scientists have now observed a new decay pattern for the first time. In this decay, a lighter form of oxygen - oxygen-13 (which has 8 protons and 5 neutrons) - decays by splitting into 3 helium nuclei (atoms without surrounding electrons), 1 proton, and 1 positron (the antimatter version of an electron).
Scientists observe this decay by watching individual atomic nuclei break apart and measuring the products of the breakup.
Scientists have previously observed interesting patterns in radioactive decay, a process known as "beta-plus decay." In this process, protons turn into neutrons and release some of the energy produced by emitting positrons and antineutrinos. After the initial beta decay, the resulting nucleus can have enough energy to boil away extra particles, making itself more stable.
This new decay mode is the first observation of beta decay releasing three helium nuclei (alpha particles) and a proton. The findings allow scientists to understand the decay process and the properties of the nucleus before decay.
An image of particles produced after a nucleus undergoes beta decay of this new decay mode. The resulting nucleus splits into three helium nuclei (α) and one proton (p), which come from a decay point (red circle). Image source: Courtesy of J.Bishop
In this experiment, researchers used the Cyclotron Institute at Texas A&M University to produce a beam of high-energy (about 10% of the speed of light) radioactive nuclei. They sent this beam of radioactive material (oxygen-13) into a device called the Texas Active Target Time Projection Chamber (TexATTPC). This material stops inside the detector, which is filled with carbon dioxide gas, and decays after about 10 milliseconds by emitting a positron and a neutrino (beta-plus decay).
The researchers implanted oxygen-13 into the detector nucleus by nucleus and waited for it to decay, then used TexATTPC to measure any particles that boiled off after beta decay. Next, they used a computer program to analyze the data to determine the trails the particles left in the gas. In this way, they were able to identify a rare event (occurring only once in every 1,200 decays) in which four particles are released after beta decay.