Radioactive BH-45M Switch

Today we will take a closer look at a radioactive, soviet switch, the BH-45M!

The production of BH-45M switches started in 1945 and continues till this day, this being said, not all of those switches are radioactive. Units produced until 1965 used radium paint but in later models, radium paint was replaced by a nonradioactive one. The very early models which were produced until early 1950s, used RaBr2 while the ones produced later used RaSO4. BH-45M switches are mainly used in military vehicles such as tanks but can also be found in some civilian ones. These switches were produced in countries of Warsaw Pact and can be found today cheaply at antique markets.

As a result of constant exposure to nuclear radiation, the paint decays and with time it loses its radioluminaces properties. Today the glow from the switch is undetectable for human eye but a photo made with a long exposure shows that there is still little bit of glow left.

Long exposure of BH-45M switch

Radium is a particularly nasty element not only because of its very high activity and radio toxicity but also because it decays into a radioactive gas called radon which in large doses can be dangerous. Luckily, the switch I have is pretty well sealed and doesn’t leak too badly, so the radon emission is relatively low.

Activity and Gamma Spectroscopy

Radium painted items range in activity anywhere from few hundred CPM to hundreds of thousands depending on the amount of radium paint used. When it comes to BH-45M switches, they are definitely are on the hotter side. The one I have measures at around 220k CPM at 1cm distance on a pancake probe and 10uSv/h gamma only at 1cm distance on my RAYSID gamma spectrometer.

Just as expected, a gamma spectroscopy of the BH-45M switch shows a very characteristic gamma spectrum for Ra226 and its decay products.

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