We have identified a brand new isotope of the rarest element in the crust of our planet.

190astatin, containing 85 protons and 105 neutrons, is the lightest isotope of astatin ever discovered and could help physicists better understand the process of alpha decay, the structure of atomic nuclei and their limits.
"Studies on new nuclei are important for understanding the structure of atomic nuclei and the limits of known matter," says physicist Henna Kokkonen from the University of Jyväskylä in Finland.

Astatine is highly radioactive and extremely unstable. It occurs in nature only as a kind of stepping stone, as a product of the decay of heavier elements, which in turn decay rapidly to lighter elements. The most stable isotope of astatine is 210astatin, which has a half-life of just over 8 hours; most of its isotopes have half-lives of less than a few seconds.

This is why it is so rare in nature; only one gram can be found on our planet at any one time. It forms, ejects protons and neutrons until it becomes a stable element, such as bismuth or radon, which then falls away again. Because it is so short-lived, its properties are largely inferred and not known with certainty.
We don't even know for sure whether it is a halogen or a metalloid. It is a rather strange element, there is no doubt about that. But studying it can help us understand not only the element itself, but also the deformation of the nuclei of different isotopes and radioactive decay.

The research was carried out using an apparatus called a gas-filled recoil separator, which is used to conduct fusion-evaporation experiments. This is when heavy ions are accelerated towards target nuclei to turn them into heavier elements, which then decay by the alpha process, ejecting alpha particles consisting of two protons and two neutrons (basically helium) until they stabilise.
The researchers fired 84strontium at target silver atoms and analysed the resulting decay products. It was not 190astatin they were looking for, but 190astatin they found.
"In my thesis, I analysed experimental data, including the new isotope," Kokkonen explains.

Previously, the most neutron-deficient isotope of the element we knew was 192astatin. The researchers analysed the new discovery and compared it with predictions from atomic mass models to see if it could tell us anything new about astatine.
It seems quite consistent with what we know about the element and its alpha decay. The isotope has a half-life of just 1 millisecond and an energy level of 7,750 kiloelectronvolts, which is quite normal. The decay is also not energetically hindered, which means it is abrupt, not delayed, which can only occur in some radioactive isotopes of heavy elements.
"I got to know the work of the Nuclear Spectroscopy group during my thesis process and summer internships," says Kokkonen. "Now I am very happy to be working in the group towards my PhD degree."

 

Source: https://www.sciencealert.com/