Scientists in Finland have discovered and measured the heaviest known nucleus that undergoes proton emission. In the process, scientists have discovered a rare isotope, 188-astatine. It has a unique watermelon-like shape, and this might unveil new kinds of nuclear interactions.
This is the first time in thirty years that the heaviest nucleus decaying via proton emission has been measured. The previous such discovery was achieved in 1996.
Radioactive decay of atomic nuclei has been a pillar in the world of nuclear physics since the beginning of nuclear research. Now, in the Accelerator Laboratory of the University of Jyväskylä, Finland, the heaviest nucleus decaying via proton emission has been measured. In proton emission, the nucleus emits a proton to achieve stability. It is a form of radioactive decay.
The new nucleus that has been discovered is the lightest known isotope of astatine. 188-At has 85 protons and 103 neutrons. These exotic nuclei are incredibly challenging and tough to study due to their short lifespan and low production cross sections. This leads to the requirement of precise techniques.
“The nucleus was produced in a fusion-evaporation reaction by irradiating natural silver target with 84Sr ion beam,” says Academy Research Fellow Kalle Auranen from the University of Jyväskylä. “The new isotope was identified using the detector setup of the RITU recoil separator.”
Alongside experimental results, the study expanded a theoretical model to interpret the gathered data. According to the model, the nucleus is highly prolate or watermelon-shaped.
The features of the nucleus indicate a trend change in the binding energy of the valence proton. This is perhaps explained by an interaction that has not been seen before in heavy nuclei.
The study is a direct follow-up of the master’s thesis of Doctoral Researcher Henna Kokkonen from the University of Jyväskylä, in which she discovered the atomic nucleus—190-At. Isotope discoveries are rare worldwide, and Kokkonen considers this an opportunity to make history a second time.
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