arXiv subjects

Patrick R. Stollenwerk

Publications and source records attributed to Patrick R. Stollenwerk.

8 recordsLinked to original sources

arXiv2025

The Auger-Meitner Radioisotope Microscope: an instrument for characterization of Auger electron multiplicities and energy distributions

We describe a new instrument, the Argonne Auger Radioisotope Microscope (ARM), capable of characterizing the Auger electron emission of radionuclides, including candidates relevant in nuclear medicine. Our approach relies on event-by-event ion-electron coincidence, time-of-flight, and spatial readout measurement to determine correlated electron multiplicity and energy distributions of Auger decays. We present a proof-of-principle measurement with the ARM using X-ray photoionization of stable krypton beyond the K-edge and identify a bifurcation in the electron multiplicity distribution depending on the emission of K-LX electrons. Extension of the ARM to the characterization of radioactive sources of Auger electron emissions is enabled by the combination of two recent developments: (1) cryogenic buffer gas beam technology to introduce Auger emitters into the detection region with well-defined initial conditions, and (2) large-area micro-channel plate detectors with multi-hit detection capabilities to simultaneously detect multiple electrons emitted in a single decay. The ARM will generate new experimental data on Auger multiplicities that can be used to benchmark atomic relaxation and decay models. This data will provide insight into the low-energy regime of Auger electrons where intensity calculations are most challenging and experimental data is limited. In particular, accurate multiplicity data of the low-energy regime can be used to inform oncological dosimetry models, where electron energies less than 500 eV are known to be most effective in damaging DNA and cell membranes.

physics.ins-det↗

arXiv2025

Enhancing reactivity of SiO$^+$ ions by controlled excitation to extreme rotational states

Optical pumping of molecules provides unique opportunities for control of chemical reactions at a wide range of rotational energies. This work reports a chemical reaction with extreme rotational excitation of a reactant and its kinetic characterization. We investigate the chemical reactivity for the hydrogen abstraction reaction SiO$^+$ + H$_2$ $\rightarrow$ SiOH$^+$ + H in an ion trap. The SiO$^+$ cations are prepared in a narrow rotational state distribution, including super-rotor states with rotational quantum number $\it{(j)}$ as high as 170, using a broad-band optical pumping method. We show that the super-rotor states of SiO$^+$ substantially enhance the reaction rate, a trend reproduced by complementary theoretical studies. We reveal the mechanism for the rotational enhancement of the reactivity to be a strong coupling of the SiO$^+$ rotational mode with the reaction coordinate at the transition state on the dominant dynamical pathway.

physics.atom-ph↗

arXiv2024

A VUV light source for enhanced production of metastable krypton and xenon beams

We demonstrate excitation of metastable krypton and xenon beams using a vacuum ultraviolet lamp and directly compare the performance of this method to metastable excitation based on a radiofrequency-driven plasma discharge. In our apparatus, lamp-based metastable excitation outperforms the plasma discharge across a wide range of beam flux values relevant for Atom Trap Trace Analysis (ATTA). Moreover, we do not observe significant degradation in lamp performance after over 160 hours of operation. We find that lamp-based excitation is particularly advantageous at the smallest and largest beam fluxes tested, demonstrating the utility of this approach both for improving krypton ATTA and for enabling the detection of radioactive xenon isotopes using ATTA. Finally, we demonstrate an additional enhancement to lamp-based metastable excitation efficiency and stability by applying an external magnetic field.

physics.atom-ph↗

arXiv2021

Precisely Spun Super Rotors

Improved optical control of molecular quantum states promises new applications including chemistry in the quantum regime, precision tests of fundamental physics, and quantum information processing. While much work has sought to prepare ground state molecules, excited states are also of interest. We demonstrate a broadband optical approach to pump trapped SiO$^+$ molecules into pure super rotor ensembles maintained for many minutes. Super rotor ensembles pumped up to rotational state $N=67$, corresponding to the peak of a 9400 K distribution, had a narrow $N$ spread comparable to that of a few-kelvin sample, and were used for spectroscopy of the previously unobserved C$^2Π$ state. Significant centrifugal distortion of super rotors pumped up to $N=230$ allowed probing electronic structure of SiO$^+$ stretched far from its equilibrium bond length.

physics.atom-ph↗

arXiv2020

Cooling of a Zero-Nuclear-Spin Molecular Ion to a Selected Rotational State

We demonstrate rotational cooling of the silicon monoxide cation via optical pumping by a spectrally filtered broadband laser. Compared with diatomic hydrides, SiO\+ is more challenging to cool because of its smaller rotational interval. However, the rotational level spacing and large dipole moment of SiO\+ allows direct manipulation by microwaves, and the absence of hyperfine structure in its dominant isotopologue greatly reduces demands for pure quantum state preparation. These features make $^{28}$Si$^{16}$O\+ a good candidate for future applications such as quantum information processing. Cooling to the ground rotational state is achieved on a 100 ms time scale and attains a population of 94(3)\%, with an equivalent temperature $T=0.53(6)$ K. We also describe a novel spectral-filtering approach to cool into arbitrary rotational states and use it to demonstrate a narrow rotational population distribution ($N\pm1$) around a selected state.

physics.atom-ph↗

arXiv2018

Prospects for Polar Molecular Ion Optical Probe of Varying Proton-Electron Mass Ratio

Molecules with deep vibrational potential wells provide optical intervals sensitive to variation in the proton-electron mass ratio ($μ$). On one hand, polar molecules are of interest since optical state preparation techniques have been demonstrated for such species. On the other hand, it might be assumed that polar species are unfavorable candidates, because typical molecule-frame dipole moments reduce vibrational state lifetimes and cause large polarizabilities and associated Stark shifts. Here, we consider single-photon spectroscopy on a vibrational overtone transition of the polar species TeH$^+$, which is of practical interest because its diagonal Franck-Condon factors should allow rapid state preparation by optical pumping. We point out that all but the ground rotational state obtains a vanishing low-frequency scalar polarizability from coupling with adjacent rotational states, because of a fortuitous relationship between rigid rotor spacings and dipole matrix elements. We project that for good choices of spectroscopy states, demonstrated levels of field control should make possible uncertainties of order $1 \times 10^{-18}$, similar to those of leading atomic ion clocks. The moderately long lived vibrational states of TeH$^+$ make possible a frequency uncertainty approaching $1 \times 10^{-17}$ with one day of averaging for a single trapped ion. Observation over one year could probe for variation of $μ$ with a sensitivity approaching the $1 \times 10^{-18}/\textrm{yr}$ level.

physics.atom-ph↗

arXiv2017

IP determination and 1+1 REMPI spectrum of SiO at 210-220 nm with implications for SiO$^{+}$ ion trap loading

The 1+1 REMPI spectrum of SiO in the 210-220 nm range is recorded. Observed bands are assigned to the $A-X$ vibrational bands $(v``=0-3, v`=5-10)$ and a tentative assignment is given to the 2-photon transition from $X$ to the n=12-13 $[X^{2}Σ^{+},v^{+}=1]$ Rydberg states at 216-217 nm. We estimate the IP of SiO to be 11.59(1) eV. The SiO$^{+}$ cation has previously been identified as a molecular candidate amenable to laser control. Our work allows us to identify an efficient method for loading cold SiO$^{+}$ from an ablated sample of SiO into an ion trap via the $(5,0)$ $A-X$ band at 213.977 nm.

physics.atom-ph↗

arXiv2016

Rotational State Analysis of AlH+ by Two-Photon Dissociation

We perform ab-initio calculations needed to predict the cross-section of an experimentally accessible (1+1') resonance-enhanced multiphoton dissociation (REMPD) pathway in AlH+. Experimenting on AlH+ ions held in a radiofrequency Paul trap, we confirm dissociation via this channel with analysis performed using time-of-flight mass spectrometry. We demonstrate the use of REMPD for rotational state analysis, and we measure the rotational distribution of trapped AlH+ to be consistent with the expected thermal distribution. AlH+ is a particularly interesting species for ion trap work because of its electronic level structure, which makes it amenable to proposals for rotational optical pumping, direct Doppler cooling, and single-molecule fluorescence detection. Potential applications of trapped AlH+ include searches for time-varying constants, quantum information processing, and ultracold chemistry studies.

physics.atom-ph↗