Although Heathkit is no longer in business, you can buy this kit from S.E. International
What the airlines never told you!
Did you know that when you travel on an airplane at altitudes of 34,000 to 37,000 feet, you are being exposed to varying radiation levels of about 260 to 280 counts per minute (CPM)? Cosmic radiation depends on your altitude and solar activity. Background radiation at sea level is about 10 CPM. After Chernobyl, I was living about 40 miles from a nuke, and being the hobbyist I am, I built the Heathkit Radiation Monitor, and took it on an airplane trip to monitor cosmic radiation at high altitude. It was amazing to see the radiation levels you are exposed to while flying at high altitude.