Our last blog entry detailed the process of fluid displacive drying and resin embedding to make sediment pucks. Once these are sliced into desired sections and polished they are inserted inside a machine that scans the samples for elemental composition. Elemental analysis is one of the various multi-proxy analysis techniques we are employing for the paleoclimate reconstruction of the amazon rainforest. Charcoal Analysis, Grain Size analysis and Loss On Ignition Organic Content Analysis are some other proxies we experiment for in our Paleoclimate wet lab. But our most priced tool is the iXRF machine, which is equipped to analyse solids, liquids and powders for elemental composition. The iXRF is multifunctional and continues to be used across fields from forensics testing, pharmaceuticals, currency notes fraud and even lead contamination testing.
How does the iXRF machine really work?
The machine has a an x-ray machine that emits x-ray fluorescence energy onto the surface of the sample. X-rays are a part of the electromagnetic spectrum and are often used in the health industry for imaging. X-ray fluorescence (XRF) is the production of x-rays in the electron orbits when inner electrons are displaced to emit XRF. The iXRF machine is fitted with an analyzer that emits these X-Rays onto the sample and as they hit atoms in the sample, the specimen releases fluorescent X-Rays. The machine is equipped to detect and measure different frequencies from the emitted rays and match them to the elements present in the sample. Each elemental fluorescent x-ray has a distinct frequency.
For our elemental analysis we use line scan data from sediment puck samples. X-ray linescans are created by acquiring X-ray data and ultimately elemental data at evenly spaced points along a horizontal line on a sample. X-ray line scans are excellent tools for determining variations in elemental composition in a block of sediment.It’s non invasive and non-disruptive such that the resin embedded sediment can be reused multiple times for accuracy or other imaging information.
Operating the iXRF
The iXRF can be operated in a vacuum, air or helium for liquid samples analysis. Settings are adjusted to the desired level e.g high count rates will improve the quality of the output data. Point dwell time is the acquire time per point on the sample. Resolution is the number of points on the line from which the x-ray data will be acquired. Increasing both produces higher quality graphics and data but lengthens the acquire time. Setting elemental properties, allows you to select the elements you want to be acquired. Intensity and concentrations, conc displays the values in weight percent.
Basic pointers for using the iXRF.
- The chamber has multiple cameras that allow you to observe the sample from different angles. The spot camera and the overview camera
- The stage is motorized such that you can control it from the screen and move the X,Y or Z axes to position the sample as close to the detector as possible.
- Position the sample at the center of the stage.
- Once the doors are closed, make sure the vacuum is turned on.
- Then before you proceed with a linescan, map scan or spectral analyses make sure the machine dashboard lights signals that the vacuum, shutter and x-rays are on.
We have been acquiring line scans from previously prepared sediment pucks and we will be plotting the data and analysing it to infer possible environmental changes. Next week we will be combining our new elemental data with charcoal data as well as observed environmental changes to infer possible patterns of paleodroughts in the Amazon rainforests near lakes like Ayauchi.
Comments
Post a Comment