How to measure/detect fluidised iron sand at 700 C in stainless steel.
Many years ago (1970s) I needed to detect fluidised iron sand heated to around 700 degrees C being pumped around a stainless steel system. I had earlier worked in the nuclear area so my solution was to use a Caesium 137 radioactive source in a lead block with a hole creating a beam whch was aimed through the stainless tube. I had a Gieger-Muller tube on the other side and counted the emissions to measure absorption, thereby detecting the presence or absence of ironsand. My question is, what solutions are available now that could achieve the same or better outcome?