I was advised to go by train as the parking at the university is apparently horrendous with the £0.6 Billion refurbishment going on! Surprisingly it was pretty dry in Leeds so the one mile walk to the Engineering section of the campus wasn't too bad.
Deep in the bowels of the Engineering Faculty run by School of Chemical and Process Engineering and the School of Earth and Environment is LEMAS. It is situated in the basement for a particular reason, minimal vibration.
As there was a gold theme for today I brought along, with the gold nugget; a gold ring, a gold stater and a gold quarter noble to show the scientists other items recovered that were crafted in gold just for curiosity on their part.
I was warmly greeted by Dr Richard Walshaw who very kindly agreed to analyse the nugget using a brand new state-of-the-art Scanning Electron Microscope (SEM) that was currently being commissioned. What a piece of kit it was too! The SEM is a Tescan Vega3 XM and has a magnification of up to 1,000,000x!
There were several rooms, each with some impressive technology and large monitors, attended by students under the wings of the doctors and professor there.
Normally, samples are ground down to a perfectly flat surface and mounted in a stable solid such as resin. Gold is sprayed onto the surface of the sample to create a conductive current when bombarded with electrons.
With the gold nugget being so valuable this was not possible so it was attached to its analysing plinth with adhesive copper tape to create a path to earth.
The nugget was mounted onto the SEM table inside the machine which was fully controlled via a desktop PC connected to three monitors. The image resolution is 8K for the SEM and 4K for the x-ray detector. What is impressive is the depth-of-field (DoF) resolution of the images.
The heavy steel door was closed and the vacuum was induced, the table and specimen were still clearly visible via a CCTV camera inside the chamber.
Once in a state of vacuum the electron beam was energised and the Secondary Electrons (SE) mode was selected and the electrons accelerated to scan speed. This creates a topographical image such as you see on usual SEM images in magazines and TV. The classic one is the ant carrying a microchip.
Several scans at varying speeds and settings were taken with the SEM image on monitor one, the internal chamber image on monitor two and the analytics on monitor three.
If you think the above is brain scattering it was even worse/better being there watching all the bits move inside the chamber, the noises of the vacuum in action, the real-time graphs showing the chemical elements of everything on the nugget and the brilliant narration from Dr Walshaw all at the same time.
Just as I thought I was getting to grips with the initial psychological storm I was hit with another; "I'm now going to analyse it using Electron Backscatter Diffraction (EBSD). With that came a brief explanation on how the electrons are scattered after hitting the targeted sample surface and then analysed by a separate x-ray detector within the chamber.
With the nugget being so uneven, an accurate analysis result may be hard to achieve so would be quantitative. It will however show the makeup of all the elements on the nugget including the soil forced into the crevices of the gold.
The brighter the area on the image the higher up the atomic scale the sample with gold being the brightest, The dark areas are the non-conductive elements such as the quartz and silica (soil and clay).
The results will be emailed in the next week or so showing the full breakdown of the elements present. From what I could see there was gold (obviously), traces of silver, iron, carbon, Oxygen, zinc and copper to name a few. A big surprise was that sea-salt was also present!
It was now three hours since entering the lab and Dr Walshaw had an appointment to keep at 1pm. He was interested in the colour difference in the stater and the quarter noble and asked if I wouldn't mind coming back at 2pm so he could check out the coins. I didn't need asking twice!
On Dr [Name Withheld] return it was back to the preparation room for the coins to be mounted on double-sided adhesive carbon pads. Again, this for the electrons to find a path to earth.
The chamber was vented after powering down the electrons and the nugget swapped places with the coins.
First up was the stater and one of the pellets selected for analysis as there may be a fairly flat area for the SEM to target. The SEM zoomed into the pellet and carried on zooming in until minute scratches on the surface of the pellet could be seen. I thought "wow" until the SEM zoomed into the scratch which looked like the Grand Canyon!
Zooming out again a flat area was identified and several parts of the area were targeted for the electrons to strike.
As the fire button was hit a graph appeared on the third screen showing the breakdown of the elements present. Mostly gold with a larger amount of silver and small amounts of copper and other trace elements.
Again, the full results will follow soon.
The gold hammered quarter noble of Edward III was next in the firing line literally. The surprise here was that the coin came back as pure gold with virtually no silver content at all!
It was now 4:20pm and the machine was vented and shut down for the day and what a lovely long day it was too starting at 10am!
The lab are next going to test some 3D software with the new SEM and I was asked if I could come back with the stater at some point as it would make a good specimen to try out. As though I'd say no!
All the images of the day can be seen here.
Acknowledgements to Dr Richard Walshaw and Dr Robert Chapman of Leeds University's LEMAS Centre.