if you look at the extended periodic table there are several place holders for predicted but undiscovered elements. unbibium (Ubb) is one such element until some scientists (see bellow) published a paper on their discovery of Ubb. Ubb is a g-series element homologous to the same f-series element Thorium (Th) in the same period (2), having a +4 oxidation state.
Ubb was not synthesized. instead it was found in a sample of purified natural Thorium. mass measurements were made of various atomic species. the paper describes their observations.
some extracts from the original paper
The question “how heavy can a nucleus be” is a fundamental problem in nuclear physics. Experimentally, elements up to Z=118 have been produced synthetically by heavy-ion reactions, with the half-lives of the Z=106 to 118 nuclei ranging from a few minutes to about a millisecond. However, in a recent study of natural Th substances, long-lived isomeric states with estimated half-lives t½ ≥ 108 y, 16 to 22 orders of magnitude longer than their corresponding ground states (g.s.), have been observed in the neutron-deficient Th nuclei. It has been hypothesized that they might belong to the recently discovered class of long-lived high spin isomeric states in the second minimum
(superdeformed (SD) minimum) and/or in the third minimum (hyperdeformed (HD) minimum) of the nuclear potential energy when plotted as a function of deformation. This result motivated us to search for long-lived superactinide elements in natural materials.
According to the extended periodic table, the superactinides are classified as homologues of the actinides, with elements 122 and 124 placed as eka-Th and eka-U, respectively. As a working hypothesis, it is reasonable to assume that if any of the superactinide elements exists in nature they might be carried along with Th and/or U substances. Here we report evidence for the existence of a nucleus with atomic mass number 292 that was found in natural Th with
an estimated half-life of &gr;108 y and an abundance of (1-10)×10-12 relative to 232Th. Its measured mass matches the predictions for the mass of an isotope with atomic number Z=122 and also some isobars of neighbouring elements. Based on theoretical chemical predictions it is argued that it is probably element 122. Preliminary results of this work have been presented previously.
In principle, natural minerals like monazite, which is the usual source material for Th, would be the most promising materials to study. However, background was the main obstacle when looking for isotopes with relative abundance of (1-10)×10-11 in natural materials. Therefore, purified natural Th was used in our measurements.
In the present work, we performed accurate mass measurements for masses 287 to 294 in Th solutions. Evidence was obtained for the existence of an isotope with a mass that matches the predictions for atomic mass number 292 and Z around 122. Here we describe this observation.
In summary, mass spectral evidence has been obtained for the existence of a long-lived superheavy isotope with an atomic mass number of 292 and t½ ≥ 108 y. Based on predicted chemical properties of element 122, it is probable that the isotope is 292, but a somewhat higher Z cannot absolutely be excluded. Because of its long lifetime, it is deduced that a long-lived isomeric state rather than the normal g.s. was observed at A=292. The hypothesis that it is a high spin SD or HD isomeric state is discussed.
abstract of the paper
Evidence for a long-lived superheavy nucleus with atomic mass number A=292 and atomic number Z=~122 in natural Th
A. Marinov, I. Rodushkin, D. Kolb, A. Pape, Y. Kashiv, R. Brandt, R.V. Gentry, H.W. Miller
(Submitted on 24 Apr 2008)
Evidence for the existence of a superheavy nucleus with atomic mass number A=292 and abundance (1-10)×10-12 relative to 232Th has been found in a study of natural Th using inductively coupled plasma-sector field mass spectrometry. The measured mass matches the predictions [1,2] for the mass of an isotope with atomic number Z=122 or a nearby element. Its estimated half-life of t½ ≥ 108 y suggests that a long-lived isomeric state exists in this isotope. The possibility that it might belong to a new class of long-lived high spin super- and hyperdeformed isomeric states is discussed.