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Register a new userIsotope Shifts in the 7s$rightarrow$8s Transition of Francium: Measurements and Comparison to textit{ab initio} Theory
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We observe the electric-dipole forbidden $7srightarrow8s$ transition in the francium isotopes $^{208-211}$Fr and $^{213}$Fr using a two-photon excitation scheme. We collect the atoms online from an accelerator and confine them in a magneto optical trap for the measurements. In combination with previous measurements of the $7srightarrow7p_{1/2}$ transition we perform a King Plot analysis. We compare the thus determined ratio of the field shift constants (1.230 $pm$ 0.019) to results obtained from new ab initio calculations (1.234 $pm$ 0.010) and find excellent agreement.
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Generally, turn-to-turn fluctuations of synchrotron radiation power in a storage ring depend on the 6D phase-space distribution of the electron bunch. This effect is related to the interference of fields radiated by different electrons. Changes in the relative electron positions and velocities inside the bunch result in fluctuations in the total emitted energy per pass in a synchrotron radiation source. This effect has been previously described assuming constant and equal electron velocities before entering the synchrotron radiation source. In this paper, we present a generalized formula for the fluctuations with a non-negligible beam divergence. Further, we corroborate this formula in a dedicated experiment with undulator radiation in the Integrable Optics Test Accelerator (IOTA) storage ring at Fermilab. Lastly, possible applications in beam instrumentation are discussed.
The large reported $E2$ strength between the $2^+$ ground state and $1^+$ first excited state of $^8$Li, $B(E2; 2^+ rightarrow 1^+)= 55(15)$ e$^2$fm$^4$, presents a puzzle. Unlike in neighboring $A=7-9$ isotopes, where enhanced $E2$ strengths may be understood to arise from deformation as rotational in-band transitions, the $2^+rightarrow1^+$ transition in $^8$Li cannot be understood in any simple way as a rotational in-band transition. Moreover, the reported strength exceeds textit{ab initio} predictions by an order of magnitude. In light of this discrepancy, we revisited the Coulomb excitation measurement of this strength, now using particle-$gamma$ coincidences, yielding a revised $B(E2; 2^+ rightarrow 1^+)$ of $25(8)(3)$ e$^2$fm$^4$. We explore how this value compares to what might be expected in rotational, Elliott SU(3), and textit{ab initio} descriptions, including no-core shell model (NCSM) calculations with various internucleon interactions. While the present value is a factor of $2$ smaller than previously reported, it remains anomalously enhanced.
With increasing demand for accurate calculation of isotope shifts of atomic systems for fundamental and nuclear structure research, an analytic energy derivative approach is presented in the relativistic coupled-cluster theory framework to determine the atomic field shift and mass shift factors. This approach allows the determination of expectation values of atomic operators, overcoming fundamental problems that are present in existing atomic physics methods, i.e. it satisfies the Hellmann-Feynman theorem, does not involve any non-terminating series, and is free from choice of any perturbative parameter. As a proof of concept, the developed analytic response relativistic coupled-cluster theory has been applied to determine mass shift and field shift factors for different atomic states of indium. High-precision isotope-shift measurements of $^{104-127}$In were performed in the 246.8-nm (5p $^2$P$_{3/2}$ $rightarrow$ 9s $^2$S$_{1/2}$) and 246.0-nm (5p $^2$P$_{1/2}$ $rightarrow$ 8s $^2$S$_{1/2}$) transitions to test our theoretical results. An excellent agreement between the theoretical and measured values is found, which is known to be challenging in multi-electron atoms. The calculated atomic factors allowed an accurate determination of the nuclear charge radii of the ground and isomeric states of the $^{104-127}$In isotopes, providing an isotone-independent comparison of the absolute charge radii.
We report new precision measurements of the $^{20}$Ne--$^{22}$Ne isotope shift for several transitions, as well as state-of-the-art, textit{ab initio} field-shift calculations. Our results are combined with historical measurements in a global fit to obtain the isotope shifts of all fifty low-lying neon levels with high precision. These level shifts show a wealth of electronic, nuclear, and relativistic phenomena. Relying on the analogy between mass shift and fine-structure operators, we explain this plethora of neon level-shifts utilizing a small number of effective parameters in a global parametric investigation. This investigation provides a birds-eye view on the isotope shift phenomena in noble gasses. From this vantage point, we reinterpret every effort made to calculate neon mass-shifts textit{ab initio}, and show that a remarkable agreement between experiment and theory is obtained.
We report a measurement of the ratio of electric dipole transition matrix elements of cesium for the $6p,^2P_{1/2} rightarrow 7s,^2S_{1/2}$ and $6p,^2P_{3/2} rightarrow 7s,^2S_{1/2}$ transitions. We determine this ratio of matrix elements through comparisons of two-color, two-photon excitation rates of the $7s,^2S_{1/2}$ state using laser beams with polarizations parallel to one another vs. perpendicular to one another. Our result of $R equiv langle 7s ^2S_{1/2} || r || 6p ^2P_{3/2} rangle / langle 7s ^2S_{1/2} || r || 6p ^2P_{1/2} rangle = 1.5272 (17)$ is in excellent agreement with a theoretical prediction of $R=1.5270 (27)$. Moreover, the accuracy of the experimental ratio is sufficiently high to differentiate between various theoretical approaches. To our knowledge, there are no prior experimental measurements of $R$. Combined with our recent determination of the lifetime of the $7s,^2S_{1/2}$ state, we determine reduced matrix elements for these two transitions, $langle 7s ^2S_{1/2} || r || 6p ^2P_{3/2} rangle = -6.489 (5) a_0$ and $langle 7s ^2S_{1/2} || r || 6p ^2P_{1/2} rangle = -4.249 (4) a_0$. These matrix elements are also in excellent agreement with theoretical calculations. These measurements improve knowledge of Cs properties needed for parity violation studies and provide benchmarks for tests of high-precision theory.
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