Atom-at-a-time laser resonance ionization spectroscopy of nobelium

Abstract

Optical spectroscopy of a primordial isotope has traditionally formed the basis for understanding the atomic structure of an element. Such studies have been conducted for most elements and theoretical modelling can be performed to high precision, taking into account relativistic effects that scale approximately as the square of the atomic number. However, for the transfermium elements (those with atomic numbers greater than 100), the atomic structure is experimentally unknown. These radioactive elements are produced in nuclear fusion reactions at rates of only a few atoms per second at most and must be studied immediately following their production, which has so far precluded their optical spectroscopy. Here we report laser resonance ionization spectroscopy of nobelium (No; atomic number 102) in single-atom-at-a-time quantities, in which we identify the ground-state transition SP. By combining this result with data from an observed Rydberg series, we obtain an upper limit for the ionization potential of nobelium. These accurate results from direct laser excitations of outer-shell electrons cannot be achieved using state-of-the-art relativistic many-body calculations that include quantum electrodynamic effects, owing to large uncertainties in the modelled transition energies of the complex systems under consideration. Our work opens the door to high-precision measurements of various atomic and nuclear properties of elements heavier than nobelium, and motivates future theoretical work.

Laser spectroscopy studies on nobelium

“…The lowest yield was available for 252 No with a cross section of about 400 nanobarn in the reaction 208 Pb( 48 Ca,2n) 252 No. Decay losses on the filament reduced efficiency to about three precent for this shorterlived nobelium isotope [33]. The isotope shift of the 1 S 0 -1 P 1 transition between 252,253,254 No was measured and the hyperfine splitting in 253 No was observed.…”

“…Nonetheless, the 1 S 0 -1 P 1 transition as well as several Rydberg states in the nobelium isotope 254 No have been identified for the first time recently [33]. An overall efficiency about six percent was achieved using a two-step laser excitation that could be boosted for a limited time by conditioning the filament.…”

“…However, quenching collisions led to the population of a metastable state, most likely the 3 D 1 state that is close to the 1 P 1 state that was excited by the first laser pulse. This behavior was explained by a rate equation model that describes the experimental data well and allows determining the energy of the 3 D 1 state indirectly [33,34]. However, Rydberg states could be excited by the second laser from either of the two states resulting in different series.…”

Isotope shifts from collinear laser spectroscopy of doubly charged yttrium isotopes

“…The most common high-resolution form of such spectroscopy is collinear laser spectroscopy, in which a laser beam and a radioactive ion beam are overlapped in a parallel geometry. Collinear laser spectroscopy is used at many different facilities; examples include ISOLDE (CERN, Switzerland) [4], JYFL (Jyväskylä, Finland) [5], NSCL (Michigan, USA) [6], and TRIUMF (Vancouver, Canada) [7], with complementary techniques for heavy elements [8,9]. For this work, beams of neutron-rich isotopes of yttrium are uniquely available at the JYFL IGISOL IV facility.…”

Superheavy Nuclei in the Quark-Meson-Coupling Model

“…Thus experimental data on quadrupole moments of superheavy elements may provide important information, leading to some distinction between the two classes of model to be used in the superheavy region. The recent progress in laser resonance ionization spectroscopy [31,32] offers a prospect that electromagnetic moments, charge radii and isotope shifts of superheavy isotopes will be accessible experimentally in the near future.…”