Using Electron Microscope On Coins

I got to use one a long time ago working with the early ANACS group. They are not what one thinks of when imagining a microscope. They are/were more like a big desk with some instrument panels (ala NASA flight desk) and an old CRT screen plus an oscilloscope and other monitoring gear. Today they are quite a bit smaller (and I assume faster, lighter and somewhat cheaper).



This is not the same SEM I used but it's the same model. There are two types of Electron Microscopes the Scanning Electron Microscope (SEM) and the Transmission Scanning Microscope (TEM) You would want to use the SEM on a coin as the TEM require the sample to be very thin, much thinner than a coin would be. The SEM produces a 3D scan of focused electron beams in an electrically charged low vacuum chamber across the surface area. Due to the very narrow electron beam, a SEM has a large depth of field yielding a nice 3D appearance, which is useful for understanding the surface structure of a sample. A wide range of magnifications is possible, from about 10 times (about equivalent to that of a powerful hand-lens) to more than 500,000 times, about 250 times the magnification limit of the best light microscopes. Most SEMs produced today have no trouble scanning a larger area like a 300mm Microchip, but back in the era of the ANACS SEM it was a different story, most SEMs could not handle a coin the size of a US Silver dollar or double eagle, so ANACS had one custom built for their needs.

Following are some scans from a 1980 Numismatist article showing the basic set-up I got to use and a 1983 book from the ANA, showing some of the images the SEM was capable of producing.





Now mind you this is NOT the ANACS of today, this was actually at the ANA Headquarters in Colorado Springs, Colorado, behind where the library is now located and downstairs where the Museum now houses the Harry Bass exhibit. This was pre AMOS Press purchase and sale.

ANA Certification Service (ANACS) started operations in 1972 in Washington D.C., in 1976 they relocated the service to Colorado Springs at the groups headquarters. In 1979 they ordered the custom built AMRAY SEM 1200B and it was delivered around 1980 to them. (That SEM in the first photo posted above) was sold used out of a lab in Ohio for the mighty sum of $343.00 a couple of years ago. It weighed 775 pounds or about 350 kilograms, not a small thing. I don't remember how much it was new but suffice to say it wasn't a cheap purchase by any means. Probably well into the mid to high 6 figures. There is also a typo in the Numismatist article on the SEM it is from Amray (Advanced METALS Research Corp. not "Medals").







As you can tell it was great for showing seams on added mint marks and flow line interruptions. Today though with advances in digital photography and optics, I believe we can produce similar quality images without the cost and trouble of going to a SEM, not to mention the cost of running and maintaining it over the years.

Today along with low cost XRF devices to analyze metal composition in coins and medals with a really good digital microscope and high quality macro DSLR you would save literally hundreds of thousands of dollars by not purchasing a SEM. Though it was certainly neat getting some hands on time with one back when they were still mostly a thing of science fiction to most people. Besides if a situation popped up where a SEM was needed, it would be more cost effective to just pay some laboratory to do the scan for you and if it became a regular occurrence, then a lease or share deal would probably be more applicable than owning one.

Anyways I thought this might make for an interesting story as I often hear - just put it under an electron microscope. Most have no idea what that entails. I know SPP-Ottawa uses them regularly in his line of work, so maybe he will see this and pop in to fill in the holes I dug myself into. I only know enough to be dangerous. My comments may be way off base from reality on using SEMs as well, as all my experience was one week back about 40 years ago.