Atom Trap Trace Analysis

In hydrology the age of water, i.e. the time between last equilibrium with atmosphere and the sampling of the water, is of great interest. With ocean circulations, climate reconstruction and groundwater management just a few possible applications are named. By measuring the concentration of a radioactive isotope, such as 14C, the age of a water sample can be determined.

The dating range of a radioactive isotope is given by its half-life (see table). For water that is between 50 and 1000 years old, there is a dating gap for which only one isotope is available: Argon 39.

The extremely low abundance of 39Ar (~10-15) presents a challenge in measuring its concentration. So far, it has been routinely accessible only by Low-Level-Counting (LLC) in the underground laboratory in Bern requiring a sample size of several tons of water and a measuring time of several weeks.

Atom Trap Trace Analysis (ATTA) is a novel detection method based on atom optical techniques that has been realized for rare Krypton isotopes. One million year old water in the Sahara was dated with that method. The aim of this project is the realization of ATTA for 39Ar.

Our apparatus achieves an atmospheric 39Ar -count rate of 4.1(3) atoms/h. Based on that, we dated a groundwater sample of the upper Rhine Graben to 360(68) years in a measuring time of one day.

The apparatus has the potential to measure 39Ar concentrations on small samples down to less than 1 ccSTP of Argon, corresponding to about 100 ml of air, 2.5 l of water or 1 kg of ice. This opens up the way for a broader application of 39Ar as a tracer e.g. in oceanography or glaciology, where the sample sizes are typically limited to 10 l of water or 1 kg of ice respectively.

We work in close collaboration with the group of Werner Aeschbach-Hertig at the institute for environmental physics. Within the scope of this project, they have developed the instruments for degassing water in the field as well as for the extraction of argon. Moreover, a technique for extracting argon out of small amounts (~1kg) of ice has been developed.

We are currently working on increasing and stabilizing the 39Ar-count rate, which includes the development of new atom-optical techniques as well as the design of the corresponding laser components and electronical/mechanical devices.

There are open positions for PhD students as well as for Master or Bachelor students. Some possible Bachelor or Master topics are:

Activation of a former metastable argon-source and construction of an argon-source testing facility (Bachelor or Master):

  • The argon-source is one of the most important parts at our ATTA-setup and has the potential for a lot of improvements. Not only the efficiency of the excitation but also a robust system is crucial for the analysis of environmental samples. Testing new ideas independently from the main apparatus requires a separate testing facility. Such a facility consists of a vacuum system operating the source and a laser probing the metastable flux. The topic can be extended by testing the first new source designs.
  • Krypton spectroscopy and integration of Kr-85 in the existing ATTA system (Master): 85Kr with a half-life of about 10 years is a good tracer to test atmospheric contamination during separation and processing of argon samples from much older sources. The cooling transitions of argon and krypton are close to each other and can be operated by only small changes of the laser system. The first step of this project is a spectroscopy of krypton to get a reference for the laser system, which than can be integrated in the ATTA setup.
  • Digital offset-lock and automatic switching between isotopes (Bachelor or Master): In order to achieve the right frequency-offset between the reference laser and the isotope dependent cooling laser, the beat signal of these two lasers is compared to a local oscillator. Aim of this thesis is to replace this oscillator by a digital solution to increase the stability. Automatic switching between isotopes should be possible then.
  • System for baking the vacuum chamber (Bachelor): Degassing of water from the walls of the vacuum system can reduce the efficiency of our ATTA-system. To reduce the water in the system, the complete vacuum system is backed out after every opening. To make this process much more efficient an automatically controlled baking system should be developed.

This is only a selection of possible projects. If you are interested don't hesitate to contact us:

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Lab Impressions:
Colorful lasers in the NaLi lab
Recent Publications:
DFG: Systematische Verbesserung von Atom Trap Trace Anlaysis für 39Ar und deren Anwendung zur Erstellung einer tausendjährigen Paläotemperaturzeitreihe aus Grundwasser
DFG: ArTTA-10mL: Ein Instrument für die 39Ar-Datierung von kleinen Eis- und Wasserproben
ERC Advanced Grant-Horizon 2020: EntangleGen- Entanglement Generation in Universal Quantum Dynamics
DFG: Test des schwachen Äquivalenzprinzips mit Antimaterie