Isotope thickness gauges are actually transmission gauges. This means they transmit radiation through the material to be measured. Physics blessed us with an isotope (Am241) that emits constant gamma radiation at an energy level (60 keV) ideal for measuring steel. Thin steel blocks a little of the radiation, and thicker steel blocks most of it. We use a detector on the opposite side of the material and measure how much gamma radiation makes it through. The more radiation we measure at the detector, the thinner the steel must be. We calibrate our gauges using precise samples, and are able to produce extremely accurate measurements over the thickness range of .007 to .250”. This range can be increased to .312” with our optional high resolution detector head.
Aluminum is three or four times less dense than steel. However, to gamma radiation, aluminum is roughly 11 or 12 times less dense. Our sources can measure aluminum with a thickness range of .080” to 3.000”. However, most customers in the service center industry process thinner gauges of aluminum. This means that isotope thickness gauges with Am241 sources are not able to produce good measurements for those applications.
There are other problems with the thicker aluminum measurements. Gauges using gamma radiation are extremely alloy sensitive. It is possible to calibrate an Am241 gauge and have it measure one coil of thick aluminum perfectly. Then the very next coil might have a slightly different alloy composition and they measurement could be off by several percentage points.
For these reasons, Am241 isotope thickness gauges are a poor choice for the measurement of think aluminum materials. However, our AGT800 laser thickness gauge does not have any alloy sensitivity or material limitations, which makes it a perfect tool to measure aluminum. To learn more, shoot us an email Sales@AdvGauging.com or give us a call at (614) 873-6691.