A lead castle, also called a lead cave or a lead housing, is a structure composed of lead to provide shielding against gamma radiation in a variety of applications in the nuclear industry and other activities which use ionizing radiation.

This is what Wikipedia says about lead castle. In fact, to make gamma-ray spectrometry of samples of very low activity you’ll need to use a lead castle. You can see the gamma rays emitted by your sample to be measured as signal and background radiation as noise,  using a lead castle, it will shield your sample from background radiation improving signal/noise ratio of your measure. I’ve built mine from a camping inox stove, a tin can and some lead scrap.

First thing to do is search for a good inox stove of proper shape, it will be the external container of the lead castle. Second thing is buy a tin can of proper size to be burried inside the castle. It will become the inner wall of the well.

Is a good idea to cover the external surface of this tin an with 1mm of copper foil. It will supress the xray generated by the interaction of gamma rays from the sample to be tested and lead shield.

You can melt some lead with a torch into a proper steel can and pour it to form the lead shield. First, do this outside! Lead is cancirogen so, better to handle it with gloves and in open air.

I’ve then poured a 16mm thick lead shield to form the bottom of the lead castle.

Then I’ve puttend iside the inner tin can blocking it in place with the help of a 10kg hammer positioned over it. Remember the hydrostatic lift force! Lead is ultra dense, the lifting force generated by the lead displacement caused by the little tin can must be neutralized via an heavy weight object positioned over it. Finaly complete the castle pouring molten lead into the walls. This is the final result.

It will take many hours to coold down. I’ve tested it’s effectiveness putting inside it a Cs137 calibration source and measuring it with my 40x40mm NaI(Tl) scintillation probe. I’ve made two measures, one from inside and one outside the castle, keeping constant the distance between the source and crystal. Result? Take a look at the following picture.

 

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Matthias Doe sent me some pictures of how his made it’s lead castle. Take a look and thank you Matthias!