Cosmic Ray Isotopes Sciences at Dalhousie (CRISDal) Lab

Cosmogenic nuclides are used to determine exposure ages and erosion rates of landforms and sediments, and exhumation rates of catchment basins. Production rates of these radioisotopes in minerals exposed to cosmic rays are very low (i.e. tens of atoms per gram of mineral per year ), so the measurement of the radionuclides require accelerator mass spectrometry (AMS).

We use AMS facilities at

• ETH Zurich (¹⁴C)
• Lawrence Livermore National Laboratory (¹⁰BE and ²⁶AL)
• Purdue University PRIME Lab (³⁶CL and ¹⁰BE)
• A.E.Lalonde AMS Laboratory at uOttawa

Preparation of accelerator mass spectrometry targets takes a minimum of one week of mineral purification and an additional week to 10 days for target chemistry. In the case of ¹⁰Be, ²⁶Al, or ³⁶Cl the chemistry involves ion chromotography and controlled precipitations. For the ¹⁴C extraction from quartz we use a tube furnace and flux to melt the quartz and our custom built ultrahigh vacuum stainless steel extraction line to purify the ¹⁴CO₂ gas.

The wait times for accelerator mass spectrometry can be long (months), during which time the required elemental analyses are also completed, either by our in-house ICP-OES or by other instruments off campus. The time for data reduction and initial interpretation ranges from a few hours to a week. Projects that involve computation with available calculators or the development of new models or theory will take longer. We normally have samples in the quene for all isotopes.

For ¹⁰Be and ²⁶Al we average about 6 months before starting new samples. For
³⁶Cl we average about 4 months delay. For ¹⁴C we are still in development mode, so it is not possible to estimate the quene time.

Contact John Gosse for quene times, costs, and other submission questions. While our policy is first come first serve, we try to accomodate students with thesis deadlines.

Each year we train visiting students and research scientists in the sample preparation and interpretation of cosmogenic nuclide data. The benefits include development of isotope geochemistry laboratory skills, appreciation of experimental uncertainty, and the participation in preparing one's own samples. For safety and QA/QC resons it is not possible to allow untrained visitors to prepare their own targets in the first couple of batches. However, visitors who stay for months or return after being trained through a couple of batches can operate independently with limited supervision, depending on lab availability and scheduling.

The (CRISDal) Lab is interested in a range of (in some instances previously intractable) scientific problems in geomorphology and landscape evolution. These problems include stream incision and sediment flux, fault kinematics and seismic slip history, tectonic geomorphology, glacial geochronology, permafrost processes and ice dating, landslide and rock avalanche research, chronology for archeology and paleontology. We collaborate with researchers at universities and insititutions worldwide, and conduct service work for geological surveys (e.g. GSC Atlantic, GSC Ottawa, USGS, Norway).

In the past 7 years

• Alluvial fan chronostratigraphy in the Mojave Desert, Nevada, and Eastern California Shear Zone, Baja California for seismic, tectonic, and paleoclimate research.
• Age of landslides and faulted surfaces in the Andes, Himalayas, and Norway.
• Fault kinematics, crustal shortening, strain partitioning, or tectonic geomorphology in Chili, Argentina, Nepal, Tibet, Eastern California, Mexico, and Mongolia.
• Pliocene sedimentation, geochronology, and erosion in the Arctic, especially related to the Beaufort Formation.
• Glacial geology and geochronology in Baffin Island, Newfoundland and Labrador, Nova Scotia, Yukon, Andes, Mongolia, Ural Mountains.
• Chronology for Archeology and Paleontology in Mongolia and the Canadian Arctic.
• Fluvial incision history in the Grand Canyon, Southern Central Andes, and Mongolia
• Sediment flux measuements from rivers along the Texas gulf, Klondike region of the Yukon, western Canadian Arctic.