Isotope shift and search for metastable superheavy elements in astrophysical data

Abstract: Spectral lines belonging to the short-lifetime heavy radioactive elements up to Es ($Z$=99) have been found in the spectra of the Przybylski's star. We suggest that these unstable elements may be decay products of a "magic" metastable nucleus belonging to the the island of stability where the nuclei have a magic number of neutrons $N=184$. The laboratory-produced nuclei have a significantly smaller number of neutrons. To identify spectra of the $N=184$ isotopes of these nuclei and their neutron-reach superheavy decay products in astrophysical data we calculate the isotope shift which should be added to the laboratory - measured wavelenghs. The results for the isotopic shifts in the strongest optical electromagnetic transitions in No, Lr, Nh, Fl,and $Z$=120 elements are presented.

• The paper calculates isotope shifts using CI+MBPT methods to identify neutron-rich superheavy elements in astrophysical data.
• It proposes a multi-step approach combining laboratory dipole transition measurements with theoretical isotope shift adjustments.
• Findings support detecting the island of stability, potentially validating nuclear models and advancing our understanding of nucleosynthesis.

Isotope Shift and the Search for Metastable Superheavy Elements in Astrophysical Data

The research paper by Dzuba, Flambaum, and Webb presents an investigation into the isotope shifts necessary for detecting superheavy elements in astrophysical spectra. These elements are postulated to exist within the "island of stability," modeling elements like Fl (Z = 114), Ubn (Z = 120), and much heavier isotopes that are currently unsynthesized and only theoretically characterized. While heavy elements with Z > 98 are synthesized in laboratories, they are neutron-poor compared to those theorized to have a "magic" neutron number of N = 184, which contributes to their stability. The isotopes in question have not yet been discovered in nature, proposing a significant challenge and opportunity for nuclear physics.

The core objective of the study is the calculation of isotope shifts to detect superheavy elements in astrophysical spectra. The authors utilize a combination of Configuration Interaction and Many-Body Perturbation Theory (CI+MBPT) to compute the isotope shifts for elements ranging from No (Z = 102) to Ubn (Z = 120). This computational approach focuses predominantly on field shifts, assuming the mass shift can be neglected due to its relatively insignificant contribution in superheavy elements.

The authors recognize the difficulty of detecting these superheavy elements, given their dearth on Earth and the complexity inherent in their spectral analysis. A significant contribution of this work is the proposition of a multi-step approach aimed at addressing this challenge:

1. Laboratory Measurement of Dipole Transition Frequencies: Obtain frequency data of strong electric dipole transitions in laboratory-produced superheavy elements, which, while neutron-poor, provide a baseline.
2. Calculate Isotopic Shifts: Adjust these laboratory measurements with calculated isotope shifts to account for the target neutron-rich isotopes.
3. Search Astrophysical Data: Utilize these adjusted frequencies to search for signatures in astrophysical spectra.

The authors derive an analytical formula to estimate shifts between isotopes, utilizing the dependence of the nuclear radius on the nucleon number $A$, specifically $R_N \propto A^{1/3}$. They validate these formulaic results by comparing them against both theoretical calculations and available experimental data for lighter analogues, such as No, deriving isotope shift coefficients which correlate well with theoretical predictions.

The implications of this work are substantial for both theoretical and experimental nuclear physics. Discovering isotopes in the island of stability would validate theoretical models, significantly enhancing our understanding of nuclear matter under extreme conditions. Moreover, this could lead to advancements in understanding nucleosynthesis processes in high-energy astrophysical events like supernovae, where high neutron fluxes may lead to the creation of these elements. Furthermore, continued research in this area could foster the refinement of calculation methods and stimulate the development of experimental techniques to measure superheavy elements with greater accuracy.

Future work will likely dwell on refining the accuracy of isotope shift calculations, increasing the precision of transition frequency measurements, and improving methodologies for detecting these transitions in astrophysical data. Progress in these areas could eventually lead to the first observational evidence of superheavy elements in the cosmos, potentially offering insights into their formation and distribution in the universe. As the search for naturally occurring superheavy elements continues, these findings underscore the need for collaborative advances in both theoretical predictions and experimental astrophysical observations.