What are mirror cores

Mirror cores

A proton carries a positive elementary charge, a neutron is - as the name suggests - electrically neutral. So much for the external differences, because the mass of the particles differ by a mere one per thousand. So it is actually not particularly surprising that the properties of atomic nucleus pairs, in which one partner has as many neutrons as the other protons - and vice versa, are very similar. The pairs are therefore called mirror cores.

Tritium nuclei (one proton, two neutrons), for example, form such a pair with helium-3 (two protons, one neutron). The radioactive isotope of carbon 14C (six protons, eight neutrons) and oxygen-14 (eight protons, six neutrons) is another example. In both pairs, however, the number of neutrons and protons does not differ that much: in the first case it is a matter of first-order mirror nuclei, in the second case of second-order ones. But what about nuclei that have a particularly large number of neutrons or protons? Do such mirror cores differ more? Mirror cores that are so "distant" would be a good test for symmetry.

A research team from the Florida State University in Tallahassee and the Michigan State University in East Lansing it was now possible on National Superconducting Cyclotron Laboratory to create and study such a pair. To do this, the researchers directed a beam of the stable isotope argon-36 onto a beryllium sample, including the unstable one
Argon-32 (18 protons, 14 neutrons) was created - one of the two partners that had to be investigated. To do this, however, the researchers led by Paul Cottle first had to sort out the argon-32 from the remaining debris, which they managed to do magnetically.

"It was like throwing a couple of plates in the air and picking the right size from them," remembers Thomas Glasmacher. But the juggling act succeeded, and so the team was finally able to direct a beam of argon-32 nuclei onto a piece of gold. Once there, they finally stimulated the atomic nuclei of the precious metal to the next higher energy level.

Now the researchers only had to compare this stimulus with that of the mirror core. Even silicon-32 (14 protons, 18 neutrons) was an unstable isotope, but with a half-life of around a hundred years, it was much easier to handle than volatile argon. In fact, the collisions with the silicon cores also provided a similar excitation probability, which - as expected - suggests a related core structure, but also almost disappointed the researchers: "You almost want a spectacular result, such as the collapse proton-neutron symmetry, "admits Kim Lister from Argonne National Laboratory. "But these exotic seeds behave disappointingly normal."