For a long time, it has been predicted that some heavy barium nuclei will appear pear-shaped. Until recently, however, experimental confirmation was not possible, as these nuclei typically only survive for a few seconds. The existence of this strange shape has now been demonstrated through the use of radiation beam acceleration and breakthroughs in new detector technology.
This experiment demonstrated a significant improvement in the ability of radioactive ion beams by successfully accelerating the extraction of fission fragments from a strong California fission source. It also provides scarce data on strange excitation modes in atomic nuclei, which are important for deciphering the fundamental forces that work within atomic nuclei.
For decades, nuclear theorists have predicted that neutron rich barium isotopes near mass number 144 are concentrated in one of only two to three regions of the periodic table, where the atomic nucleus may actually exhibit a pear-shaped shape in the ground state, or more generally, a reflective asymmetric shape. However, for a long time, due to the short lifetime of these isotopes, which typically decay in a few seconds or less, it has been considered impossible to experimentally verify this property in barium nuclei.
But now, a team of scientists from the United States, Britain, and France has conducted a state-of-the-art experiment in the Argonne National Laboratory, finally directly measuring the shape of these atomic nuclei for the first time, providing support for theoretical predictions made decades ago.
To perform this challenging measurement, researchers collected a beam of radioactive barium ions from the fission debris of the California atomic nucleus (CARIBU source) and accelerated it (ATLAS accelerator) to a carefully adjusted energy to study the nuclear excitation generated by electromagnetic interaction in the bombardment of a pilot target.
A new generation of gamma ray tracking detectors and matched pixel avalanche charged particle detectors are used to study the radiation of excited atomic nuclei. These data provide an in-depth understanding of the nuclear structure of barium isotopes. The results show that these nuclei exhibit a pear shape, even larger than originally predicted by theory.
Barium carbonate is an inorganic compound with the molecular formula BaCO3. Like most alkaline earth metal carbonates, it is a white salt that is insoluble in water. It is a mineral called witherite. In a commercial sense, it is one of the most important barium compounds.
