I’m having construction work done on my house. The chimney breast in the kitchen is being removed to open out the space, which has turned out to be an arduous and dirty job. There have however, been some interesting surprises. At the back of the chimney breast I found an old water boiler, probably close to 100-years old, along with some lead piping. Lead from the 1920s is interesting for an unusual reason. To explain, let me switch stories for a moment to a laboratory where I once worked.
My career has, more or less, been spent measuring radioactivity emitted from medical radioisotopes. I’ve focused on measuring tiny amounts of radioactivity using various highly sensitive techniques. One technique, called autoradiography, involved tagging biological material with a radioisotope and then visualising its physiological distribution by exposing the sample to photographic film. The levels of radioactivity are small and the film is insensitive and so exposure times for the photographic plates are very long – up to several weeks. The problem with this is that radioactivity is everywhere. It comes out of the sky as cosmic radiation and it even emanates from the human body from radioactive carbon and potassium. Over long time periods the photographic plates become fogged from this background radiation.
To get around this problem, the photographic plates are placed in a box made of lead. But then there’s another problem. The atomic bomb tests of the 1960s injected small amounts of radioisotopes into the atmosphere which become trapped in molten lead as it solidifies. This small amount of radioactivity was enough to fog the plates when exposures were particularly long. The lead boxes shielding the photographic plates were therefore constructed from pre-1950s lead, hammered into shape without melting. One supplier of these boxes told me they got most of their lead from the roofs of old churches during demolition. That way they could verify the age of the lead, which was often from the Victorian age.
The lead piping from my kitchen would have therefore served well for an autoradiography box but there’s probably not enough for anyone to be interested. In the meantime, I’ve kept a sample of the piping and I’ll encase it in plastic as a reminder of a bygone age.
Graham Lappin 