Heaviest proton emitter astatine-188 detected Premium

International collaboration led by University of Jyväskylä detects and measures proton emission from heaviest proton emitter 188At isotope.

Thirty years after bismuth emitting a proton was detected and measured in 1996, an international collaboration led by researchers at the University of Jyväskylä, Finland, detected and measured the half-life of the heaviest proton emitter 188At (astatine) isotope, which decayed by emitting a proton. While isotopes often undergo radioactive decay by emitting alpha, beta, and gamma particles, rarely do they emit a proton.

The study was published in the journal Nature Communications.

“The measured half-life for the 188At is 190 microseconds, which defines the time scale for the proton emission,” Henna Kokkonen, the first and one of the corresponding authors from the University of Jyväskylä said in an email to The Hindu.

“For a nucleus with given proton and neutron numbers, if we keep on adding more protons, we will reach a limit where the last-added proton would simply drip away. Such proton-rich nuclei often decay by emitting a proton, which is a rare process and is measured with highly specialised experimental facilities and corroborated with state-of-the-art theoretical descriptions,” explained Paramasivan Arumugam, Professor in the Department of Physics at IIT Roorkee, a coauthor of the paper. “This might be occurring naturally but this was the first time that an Astatine isotope decaying by proton emission was detected and measured in a lab.”

To a question why the emission of a proton by Astatine was not detected and measured earlier, Dr. Kokkonen said: “Studies of the nuclei at this area of the nuclear chart are extremely challenging and require highly selective equipment to perform the experiments. The nuclei are challenging to produce, since the production rate is very low. The measurement techniques and the analysis have advanced significantly during the past years allowing us to study more and more exotic nuclei.”

The heaviest Astatine (At) nucleus, with an atomic number 85, was produced in a fusion-evaporation reaction by irradiating a silver target with a strontium ion beam. Of the several nuclei that were formed when the strontium beam hit the silver target, the 188At isotope was identified using a Recoil-Ion Transport Unit (RITU) recoil separator. After the emission of the proton, the 188At isotope has 84 protons and 103 neutrons.

“When the 188-astatine emits the proton, it becomes 187-polonium isotope, which has a half-life of only 1.4 milliseconds. The 187-polonium isotope then decays via alpha decay into 183-lead and so on, until it reaches a stable nucleus,” Dr. Kalle Auranen, the other corresponding author from the University of Jyväskylä, said in an email.