Atom Trap Trace Analysis

Multi-Tracer Groundwater Dating in Southern Oman Using Bayesian Modeling

Spurensuche in der Umwelt

https://www.pro-physik.de/physik-journal/november-2021

Dating glacier ice of the last millennium by quantum technology

Radiometric dating with ³⁹Ar covers a unique time span and offers key advances in interpreting environmental archives of the last millennium. Although this tracer has been acknowledged for decades, studies so far have been limited by the low abundance and radioactivity, thus requiring huge sample sizes. Atom trap trace analysis, an application of techniques from quantum physics such as laser cooling and trapping, allows us to reduce the sample volume by several orders of magnitude compared with conventional techniques. Here we show that the adaptation of this method to ³⁹Ar is now available for glaciological applications, by demonstrating the entire process chain for dating of alpine glacier ice by argon trap trace analysis (ArTTA). Ice blocks as small as a few kilograms are sufficient and have been obtained at two artificial glacier caves. Importantly, both sites offer direct access to the stratigraphy at the glacier base and validation against existing age constraints. The ice blocks obtained at Chli Titlis glacier at 3,030 m asl (Swiss Alps) have been dated by state-of-the-art microradiocarbon analysis in a previous study. The unique finding of a bark fragment and a larch needle within the ice of Schaufelferner glacier at 2,870 m asl (Stubai Alps, Austria) allows for conventional radiocarbon dating. At both sites the existing age information based on radiocarbon dating and visual stratigraphy corroborates the ³⁹Ar ages. With our results, we establish argon trap trace analysis as the key to decipher so far untapped glacier archives of the last millennium.

Ar-39 dating with small samples provides new key constraints on ocean ventilation

Ocean ventilation is the integrated effect of various processes that exchange surface properties with the ocean interior and is essential for oxygen supply, storage of anthropogenic carbon and the heat budget of the ocean, for instance. Current observational methods utilise transient tracers, e.g. tritium, SF6, CFCs and 14C. However, their dating ranges are not ideal to resolve the centennial-dynamics of the deep ocean, a gap filled by the noble gas isotope 39Ar with a half-life of 269 years. Its broad application has been hindered by its very low abundance, requiring 1000 L of water for dating. Here we show successful ³⁹Ar dating with 5 L of water based on the atom-optical technique Atom Trap Trace Analysis. Our data reveal previously not quantifiable ventilation patterns in the Tropical Atlantic, where we find that advection is more important for the ventilation of the intermediate depth range than previously assumed. Now, the demonstrated analytical capabilities allow for a global collection of ³⁹Ar data, which will have significant impact on our ability to quantify ocean ventilation.

Bichromatic force on metastable argon for atom-trap trace analysis

For an efficient performance of atom-trap trace analysis, it is important to collimate the particles emitted from an effusive source. Their high velocity limits the interaction time with the cooling laser. Therefore, forces beyond the limits of the scattering force are desirable. The bichromatic force is a promising candidate for this purpose which is demonstrated here on metastable argon-40. The precollimated atoms are deflected in one dimension and the acquired Doppler shift is detected by absorption spectroscopy. With the experimentally accessible parameters, it was possible to measure a force three times stronger than the scattering force. Systematic studies on its dependence on Rabi frequency, phase difference, and detuning to atomic resonance are compared to the solution of the optical Bloch equations. We anticipate predictions for a possible application in atom-trap trace analysis of argon-39 and other noble gas experiments, where a high flux of metastable atoms is needed.

Groundwater dating with Atom Trap Trace Analysis of 39Ar

We report on the realization of Atom Trap Trace Analysis for ³⁹Ar and its first application to dating of groundwater samples. The presented system achieves an atmospheric ³⁹Ar count rate as high as 3.58 ± 0.10 atoms/h allowing for the determination of the ³⁹Ar concentration in less than a day. We demonstrate that the measured count rates are proportional to the ³⁹Ar concentration by intercomparison with Low-Level Counting results and by measurements on prepared argon samples with defined concentration. For a geophysical application, we degas three different groundwater samples and gas chromatographically extract the argon. The ³⁹Ar ages inferred from the count rates extend over the accessible dating range and are in agreement with the Low-Level Counting results as well as with complementary isotope data.

Single spontaneous photon as a coherent beamsplitter for an atomic matter-wave

In spontaneous emission an atom in an excited state undergoes a transition to the ground state and emits a single photon. Associated with the emission is a change of the atomic momentum due to photon recoil. Photon emission can be modified close to surfaces and in cavities. For an ion, localized in front of a mirror, coherence of the emitted resonance fluorescence has been reported. Previous experiments demonstrated that spontaneous emission destroys motional coherence. Here we report on motional coherence created by a single spontaneous emission event close to a mirror surface. The coherence in the free atomic motion is verified by atom interferometry. The photon can be regarded as a beamsplitter for an atomic matter-wave and consequently our experiment extends the original recoiling slit Gedanken experiment by Einstein to the case where the slit is in a robust coherent superposition of the two recoils associated with the two paths of the quanta.

Towards the realization of atom trap trace analysis for ³⁹Ar

We present our study of the realization of atom trap trace analysis for ³⁹Ar, an ultra-sensitive detection method for rare isotopes based on laser cooling. We report on the experimental determination of the hyperfine spectrum of the relevant cooling transition. A high-intensity, optically collimated beam of metastable argon atoms has been set up, and fluorescence detection of single ⁴⁰Ar atoms ina magneto-optical trap is realized. The deduced efficiencies of each stage lead to an expected ³⁹Ar count rate of six atoms per hour in the final setup.

 

 

Hyperfine spectroscopy of the 1s5−2p9 transition of 39Ar

We report on the first experimental determination of the hyperfine structure of the 1s₅-2p₉ transition in ³⁹Ar . We give a detailed description of the sample preparation, spectroscopy cell cleaning, and spectroscopic setup. The resulting set of parameters consists of the hyperfine constants of the levels involved and the isotopic shift between ³⁹Ar and ⁴⁰Ar . With the achieved precision all laser frequencies necessary for the implementation of atom trap trace analysis for ³⁹Ar , i.e., laser cooling and repumping frequencies, are now known.