Unoctseptium, Uos, is the temporary name for element 187. Nuclides of this element are likely to be possible. While the structures are possible, this element can't form.

NUCLEAR PROPERTIES

No predictions for half-life or decay modes are available for elements with Z > 175. It is possible to determine a boundary in the (Z,A) {or (Z,N)} plane outside of which no nuclides are possible, as detailed in "The Final Element", this wiki.

A nuclear drop containing 187 protons and more than 633 neutrons must decay by neutron emission with a half-life under 10^-14 sec. A drop with 187 protons and fewer than 288 neutrons must decay by spontaneous fission with a half-life under 10^-14 sec. Nuclear drops in the band from Uos 820 to Uos 475 are not required to decay either by neutron emission or by fission, so it is possible they will survive the 10^-14 sec needed for them to become nuclides.

The boundary described above was arrived at by applying large factors of safety to quantities which have been predicted. By looking at which factors apply to a particular (Z,A) point, it is possible to make a qualitative guess how likely it is that (Z,A) is a nuclide. Details of this method are given in "Nuclear Guesswork", this Wiki. What follows should not be considered predictions, only guesses as to what might be. Likelihood that a nuclide can exist are given in four categories: likely, unlikely, improbable, and not impossible.

Nuclear drops in the bands Uos 820 to Uos 796 and Uos 716 to Uos 691 are likely to decay by neutron emission but are stable against fission. Nuclides in these bands are unlikely. Drops in the bands Uos 795 to Uos 717 and Uos 690 to Uos 684 are likely to decay by neutron emission and require a moderate amount of structural correction energy. Nuclides in these bands are improbable. Drops in the band Uos 595 to Uos 586 are unlikely to decay by neutron emission and are stable against fission. Nuclides in this band are likely. Drops in the bands Uos 683 to Uos 596 and Uos 585 to Uos 541 are unlikely to decay by neutron emission and require a moderate amount of structural correction energy. Nuclides in these bands are unlikely. Drops in the band Uos 540 to Uos 475 are unlikely to decay by neutron emission but require large structural correction. Nuclides in this band are improbable.

OCCURRENCE

FORMATION

Uos 595 to Uos 586 are likely to be nuclides. Depending on the neutron dripline's actual location, nuclei in this A range may form when material over 700 - 800 meters deep is ejected from a neutron star during a merger. (See "Neutron Star", this Wiki.). Uos is too far from the neutron dripline for any of its isotopes to form directly, and most beta-decay chains from nuclides with suitable A terminate in fission at lower Z. It is, theoretically, possible for Uos 588 to Uos 586, to form via beta decay, but attrition due to fission and beta+neutron(s) decays make actual formation impossible in practice.

It is implausible that neutron capture can form any Uos isotope.

PERSISTENCE

Since Uos can't form, how long it lasts is irrelevant.

ATOMIC PROPERTIES

The nuclear charge of Uos is so great that stationary-state orbital theory cannot describe its electrons. In addition, both nuclear size and nuclear shape may affect its electron structure. If these effects are small, and if the assumptions made in "Period 9 Elements" (this wiki) are valid, Uos will be a 9th period active metal.

REFERENCES

References are given in the articles cited.

(05-28-20)

Community content is available under CC-BY-SA unless otherwise noted.