A lead castle, also called a lead cave or a lead housing, is a structure composed of brick

Brick

A brick is a block of ceramic material used in masonry construction, usually laid using various kinds of mortar. It has been regarded as one of the longest lasting and strongest building materials used throughout history.-History:...

s made of lead

Lead

Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...

. Lead castles are a type of lead shielding

Lead shielding

Lead shielding refers to the use of lead as a form of radiation protection to shield people or objects from radiation. Lead can effectively attenuate certain kinds of radiation because of its high density and high atomic number; principally, it is effective at stopping alpha rays, gamma rays, and...

 and are used to enclose small radioactive sources and/or radiation detectors. They are used during nuclear

Nuclear reaction

In nuclear physics and nuclear chemistry, a nuclear reaction is semantically considered to be the process in which two nuclei, or else a nucleus of an atom and a subatomic particle from outside the atom, collide to produce products different from the initial particles...

 research and testing. The castle may enclose the radioactive source to shield people from radiation or it may be used to shield sensitive detectors from ambient gamma radiation. If the experiment is to be observed, a viewing window of lead glass

Lead glass

Lead glass is a variety of glass in which lead replaces the calcium content of a typical potash glass. Lead glass contains typically 18–40 weight% lead oxide , while modern lead crystal, historically also known as flint glass due to the original silica source, contains a minimum of 24% PbO...

 may be used. A typical lead brick weighs about ten kilograms. Lead castles can be made of hundreds of bricks and weigh thousands of kilograms, so the floor must be able to withstand a heavy load. It is best to set one up on the ground floor or basement of a building built on a concrete

Concrete

Concrete is a composite construction material, composed of cement and other cementitious materials such as fly ash and slag cement, aggregate , water and chemical admixtures.The word concrete comes from the Latin word...

slab. If the castle is not put directly on the floor, it will require a very strong structure to safely support it.