Exotic Nuclei

We produce and study molecules containing rare and exotic nuclei for applications in fundamental symmetries, nuclear structure, nuclear astrophysics, and fundamental chemistry.

There are many unique reasons to study molecules with short-lived, radioactive nuclei.  To name just a few:

• Sensitivity to fundamental symmetry violations, such as those discussed on our Research Overview page, scales rapidly with the number of proton number, meaning that heavier species are intrinsically more sensitive.  At some point, sufficiently heavy species become short-lived and radioactive.

• Certain unstable nuclei, in particular actinides, have an exotic "pear shape" (octupole deformation) in their mass distribution, which significantly enhances sensitivity to fundamental symmetry violations in the nucleus.

• The electrons in an atom or molecule can be used as sensitive probes of the nucleus, for example the mass, charge, shape, magnetism, and more.  Comparing nuclei with extreme numbers of neutrons or protons enables high precision measurement comparison of these properties, but also requires access to nuclei which are not stable.

• The observation of nuclei created in space, for example in supernovae, gives information about important astrophysical processes.  Nuclei which are unstable provide a natural time-stamp about when and therefore where it was produced - if the nucleus is still around, we know that it must have been created not much longer ago than its half-life. 

• The chemical properties of the heaviest atoms and molecules are challenging to study, both experimentally and theoretically, leaving regions of the periodic table which are relatively unexplored.

Despite the many applications, the experimental study of molecules with short-lived nuclei remains extremely limited.  The challenges stem from the fact that studying ever regular molecules with precision is difficult - even the "simplest" molecules have a surprisingly complex structure, many of interest are chemically unstable, and their spectra become rapidly more complicated as their temperature increases.  The steps needed to chemically synthesize, cool, and study molecules with high precision is challenging, even for species containing stable nuclei which can be purchased from chemical supply companies by the kilogram. 

We have adapted and extended our methods for synthesizing, cooling, and precisely studying polyatomic molecules to those containing radioactive nuclei.  This enables rapid, broadband, high precision, gas-phase spectroscopy starting with extremely small (few microgram) quantities of chemical precursors.

Radium-Containing Molecules

One of the most interesting radioactive species for molecular studies is radium.  It has a highly deformed nucleus with large amplification of the effects of fundamental symmetries, and makes laser-coolable polyatomic molecules which enables the application of advanced quantum control.  We currently create RaOH molecules in a cryogenic buffer gas cell by combining laser ablation of microgram-scale radium-226 samples with excited state chemistry by driving the radium 1S0-3P1 line.  We then perform spectroscopy on the resulting cold (4 K) molecules using laser-induced fluorescence.

Relevant publications:

• Review: Opportunities for Fundamental Physics Research with Radioactive Molecules
  G. Arrowsmith-Kron et al., arXiv:2302.02165 (2023)

• CP-violation sensitivity of closed-shell radium-containing polyatomic molecular ions
  K. Gaul, N. R. Hutzler, P. Yu, A. M. Jayich, M. Iliaš, A. Borschevsky
  arXiv:2312.11687 (2023)

• Relativistic coupled-cluster calculations of RaOH pertinent to spectroscopic detection and laser cooling
  C. Zhang,   P. Yu, C. J. Conn, N. R. Hutzler,  L. Cheng
  Phys. Chem. Chem. Phys. 25, 32613 (2023)

• Intensity-borrowing mechanisms pertinent to laser cooling of linear polyatomic molecules
  C. Zhang, N. R. Hutzler, L. Cheng
  J. Chem. Theory Comput. 19, 4136 (2023)

• Probing Fundamental Symmetries of Deformed Nuclei in Symmetric Top Molecules
  P. Yu, N. R. Hutzler
  Phys. Rev. Lett. 126, 023003 (2021)

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