Scientists may have reached a new level of understanding when it comes to the question of how heavy metallic elements originated, thanks to an isotope of tin. By bombarding tin-132 with neutrons, researchers have been able to gather some details on how unstable nuclei incorporate new nucleons. Aside from new knowledge about the behavior of unstable atoms, the experiment may also give some insight into how stars can create many of the heavy elements, including gold and platinum.

Tin-132 is a "double magic" isotope of tin, meaning it is significantly more stable than the next size up, tin-133, thanks to its proton and neutron counts. Tin-132 is pretty unstable, with a half-life of only 40 seconds, but giving it one more neutron (tin-133) makes it significantly more unstable. Magic nuclei hate it when new neutrons crash their party.

Because tin-132 is so short-lived, researchers have tapped it as good approximation for ions that take part in a process known as rapid neutron capture. The rapid neutron capture process, or r-process, is thought to take place inside of supernovae or collisions of neutron stars, and it sounds like an alchemist's dream—it lets heavy elements like iron turn into new ones like gold, and may account for the origin of many heavy elements.

The r-process works like this: huge amounts of neutrons fly around in a supernova and collect in nuclei, making them extremely unstable. Eventually, the atom decays and converts a neutron into a proton, turning it into a new element.

The problem with the r-process theory is that scientists are fuzzy on the details of what neutron capturing might look like in an unstable atom, because capture and decay would both happen so fast. To get a better picture, they'd need to throw neutrons at an unstable atom that already doesn't want any more neutrons. If researchers could get the neutrons to stick, even briefly, they could see how an unstable atom deals with them.

To accomplish this, researchers bombarded a uranium-carbide target with protons to induce fission. This resulted in deuterons, particles consisting of a proton and neutron, chipping off the target. Researchers then collided these deuterons with a stream of negative tin-132 ions to get the tin-132 to connect with one of the deuterons.

Once they hit each other, a tin-132 ion would take the neutron from the deuteron and send the proton spinning away. A detector then caught the protons and measured their quantum states, allowing researchers to infer the state the neutron occupied as it attached briefly to the tin ion.

Contrary to normal behavior, the tin ions did not always shuffle their new neutron into the lowest possible energy slot. Instead, the ions regularly placed the neutron in one of three excited states within the nucleus, including one state that has never been experimentally observed before. This indicates that the r-process, while not straightforward, may actually be fairly predictable.

The experiment seems pretty specialized, but researchers are hoping they can extrapolate tin-132's neutron collection behavior to other unstable nuclei, like the ones that may actually take part in the r-process inside of stars. If unstable ions do place neutrons into excited slots without filling the lower energy slots below them first, knowing this would allow scientists to make better guesses about how exactly the r-process happens.

If the r-process checks out, researchers will have a pretty good guess as to the origin of several of the heavy elements. Future experiments may include studying iron's rapid neutron capture behavior, as well as a small-scale r-process simulation.

Nature, 2010. DOI: 10.1038/nature09048 (About DOIs).