Finland just synthesized the heaviest proton-emitting isotope ever seen

In a modest underground lab in Jyväskylä, Finland, something very strange and very heavy was born.

It wasn’t forged in a massive collider. It didn’t require kilometers of magnets or billions of dollars in funding. What emerged, instead, was an atom shaped like a sliced watermelon—and it may be rewriting the rules of nuclear structure.

Meet Astatine-188, the heaviest atomic nucleus ever observed that can emit a proton. It lives for less than a millisecond, bends expectations like soft clay, and challenges decades-old models that physicists once held as near-certain.

You can also read:

• They fused carbon like stars do — And caught it on camera
• The dream of wireless power is back—and this time, it might actually work !

A nucleus that shouldn’t exist, but does anyway

The new isotope, ¹⁸⁸At, has 85 protons and 103 neutrons. That technically makes it one of the lightest known isotopes of astatine—but paradoxically, it is now the heaviest proton emitter ever discovered. That’s not just a quirky footnote. It forces theorists to rethink how protons bind inside the nucleus, especially in borderline-stable configurations.

The production method was classic but effective. Researchers at the University of Jyväskylä fired a beam of strontium-84 ions at a natural silver target (¹⁰⁷Ag). The resulting nuclear reaction—specifically a fusion-evaporation process—caused three neutrons to be ejected, leaving behind a rare and highly unstable isotope: ¹⁸⁸At.

Detection was achieved using the RITU recoil separator, a device that filters atoms based on their mass and trajectory. Only a few ¹⁸⁸At nuclei are created per hour, buried in a storm of irrelevant nuclear debris.

A nuclear watermelon: prolate and proud

Here’s where the real weirdness begins. This atom doesn’t look like a sphere. It doesn’t even try. Its nucleus is stretched—technically “prolate”—resembling an oval melon standing on its end.

This geometry is more than aesthetic. It changes how particles behave inside the nucleus. Most notably, it should make proton emission less likely. Theoretical models, up until now, did not expect this configuration to allow a proton to escape. Yet, ¹⁸⁸At does it anyway.

The emission likely involves subtle shifts in the binding energy of the valence proton, that final proton teetering on the edge of nuclear stability. The fact that it escapes suggests we’ve been underestimating how deformation affects nuclear decay.

Proton emission: the unicorn of decay modes

In the zoo of radioactive decay, proton emission is rare. It only occurs in nuclei that are so proton-rich, they start ejecting them like passengers from an overloaded bus.

Before now, the heaviest known proton emitter was Bismuth-185, discovered back in 1996. Astatine-188 has now shattered that record.

Proton emission is fascinating because it involves quantum tunneling: the proton shouldn’t have enough energy to escape the nuclear potential barrier, but somehow it does, teleporting through the wall like a subatomic Houdini.

Chasing ghosts with precision instruments

Detecting an atom that exists for less than one millisecond is like photographing a lightning bolt with a pinhole camera. The team used a chain of ultra-sensitive detectors to isolate the short-lived signature of a proton being emitted.

Each proton release is subtle—a tiny blip in a sea of signals. The RITU separator focuses the atomic fragments, allowing researchers to trap the rare nucleus and analyze its decay before it vanishes.

The challenge wasn’t just technical. It was also statistical. Only a handful of useful events occurred amid billions of unwanted reactions.

From a master’s thesis to international headlines

At the center of this story is Henna Kokkonen, a doctoral researcher whose work is drawing worldwide attention. She had already helped identify another astatine isotope—¹⁹⁰At—during her master’s studies in 2023.

Now she’s leading the charge into nuclear terra incognita. “You don’t discover a new nucleus every day,” she remarked. Her work combines high-risk experimental setups with the kind of patience usually reserved for clockmakers.

More than a physics milestone, the discovery is a reminder: the atomic nucleus is still full of surprises.

Shaking the theoretical foundations—again

The implications of ¹⁸⁸At go far beyond Jyväskylä. Nuclear structure models, which attempt to predict decay patterns and binding energies, will have to be re-evaluated. That matters not just for lab experiments, but for understanding how elements behave in neutron stars or during stellar nucleosynthesis.

The shape, decay, and structure of this one exotic isotope may hint at new types of interactions between protons in high-mass nuclei. The equations that govern such systems may need correction—not tweaks, but revisions of core terms and assumptions.

When a real-world experiment contradicts the best theories, the theories must bend.

Technical snapshot of 188At

In a world of megascale physics experiments, sometimes the most disruptive insights come from the smallest, shortest-lived atoms. Astatine-188 reminds us: the nucleus is neither quiet nor solved.

Reference:

Kokkonen, H., Auranen, K., Siwach, P. et al. New proton emitter ¹⁸⁸At implies an interaction unprecedented in heavy nuclei. Nat Commun 16, 4985 (2025). https://doi.org/10.1038/s41467-025-60259-6

Source Image: Background of the atom hologram showing the remix of scientific technology from the hand of man (Freepik)

Share on Facebook

Post on X

Follow us

Save