Discovery of four protons and four neutrons at the Riken RI Beam Factory in Tokyo, Japan for the production of O16, O28 and oxygen-24
Current theories state that atomic nuclei with certain numbers of protons and neutrons are inherently stable. This is because protons and neutrons fill up ‘shells’ in the nucleus. When a shell is filled with just the right number of protons or neutrons, it becomes massively difficult to add or take away particles. These numbers are thought to have included 2, 8, 20, 28, 50, 22 and 126 particles. The magic number of both protons and neutrons in a nucleus makes it more stable.
The strongest force in the Universe is the one that holds together the protons and neutrons in an atom’s nucleus. To unlock how elements are forged, the physics of neutron stars and more, scientists need to better understand this strong nuclear force, says Takashi Nakamura, a physicist at the Tokyo Institute of Technology. He and other researchers are testing theories about how atomic nuclei are held together by pushing them to extremes. Load lightweight nucleus such as oxygen with excess neutrons to see what happens.
O16 is doubly magic because of it’s eight protons and eight neutrons. It has long been predicted that Oxygen-28 with 8 protons and 20 neutrons would be doubly magic. But physicists have not been able to detect it before.
Observing O28 required several experimental feats. The Riken RI Beam Factory in Wako, Japan was the key to the entire operation. The scientists created a isotope of calcium-48 from firing a beam at a target. The nucleus of this isotope has more protons than vowels. The same number of plutonium and x-rays. After smashing F29 into a thick barrier of liquid hydrogen the scientists knocked a proton out of the nucleus and produced O28.
The rare form of oxygen was not long enough to be seen. Instead, the team detected its decay products: oxygen-24 plus four neutrons, a measurement that seemed impossible only a few years ago.
This is the first time that scientists have detected four at the same time, and it’s the only time that has been done before. He says they are like ghosts. It is impossible to wrangle neutrons with the same procedure that protons can go through, with no electrical charge. To observe individual neutrons, the team used a powerful detector built for that purpose, on loan from the GSI Helmholtz Centre for Heavy Ion Research in Darmstadt, Germany, in addition to Riken’s instruments. When the protons knock around the incoming neutrons are revealed. Nakamura says that the study’s lead author, Tokyo Institute of Technology physicist Yosuke Kondo, used simulations to help to verify these tricky measurements.
“They’ve really done their homework,” says Robert Janssens, a physicist at the University of North Carolina at Chapel Hill. They did all of the checks for you. It is a tour de force.
The Fate of the O28 Isotope and the Limits of Nucleology, Revealed by Janssens
Although the team wasn’t able to get an exact measurement of the lifetime of O28, Nakamura says that the isotope did not behave as if it were doubly magic — it fell apart almost as soon as it came into existence.
It is simple and complicated, according to Janssens. He said they didn’t know how many protons and neutrons you could put together in a nucleus. What is the limit in other words?