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

lead Lead is a chemical element with the symbol Pb (from the Latin ) and atomic number 82. It is a heavy metal that is denser than most common materials. Lead is soft and malleable, and also has a relatively low melting point. When freshly cu ...

to provide shielding against

gamma radiation A gamma ray, also known as gamma radiation (symbol γ or \gamma), is a penetrating form of electromagnetic radiation arising from the radioactive decay of atomic nuclei. It consists of the shortest wavelength electromagnetic waves, typically s ...

in a variety of applications in the

nuclear industry Nuclear power is the use of nuclear reactions to produce electricity. Nuclear power can be obtained from nuclear fission, nuclear decay and nuclear fusion reactions. Presently, the vast majority of electricity from nuclear power is produced ...

and other activities which use

ionizing radiation Ionizing radiation (or ionising radiation), including nuclear radiation, consists of subatomic particles or electromagnetic waves that have sufficient energy to ionize atoms or molecules by detaching electrons from them. Some particles can travel ...

Applications

Shielding of radioactive materials

Castles are widely used to shield radioactive "sources" ''(see notes)'' and radioactive materials, either in the laboratory or plant environment. The purpose of the castle is to shield people from

. Lead will not efficiently attenuate

neutrons The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the nuclei of atoms. Since protons and neutrons behave ...

. If an experiment or pilot plant is to be observed, a viewing window of

lead glass Lead glass, commonly called crystal, is a variety of glass in which lead replaces the calcium content of a typical potash glass. Lead glass contains typically 18–40% (by weight) lead(II) oxide (PbO), while modern lead crystal, historically als ...

may be used to give gamma shielding but allow visibility.

Shielding of radiation detectors

Plant radiation detectors that are operating in a high ambient gamma background are sometimes shielded to prevent the background swamping the detector. Such a detector may be looking for alpha and beta particles, and gamma radiation will affect this. Laboratory or

health physics Health physics, also referred to as the science of radiation protection, is the profession devoted to protecting people and their environment from potential radiation hazards, while making it possible to enjoy the beneficial uses of radiation. He ...

detectors, even if remote from nuclear operations, may require shielding if very low levels of radiation are to be detected. This is the case with, for instance, a

scintillation counter A scintillation counter is an instrument for detecting and measuring ionizing radiation by using the excitation effect of incident radiation on a scintillating material, and detecting the resultant light pulses. It consists of a scintillator w ...

measuring low levels of contamination on a swab or sample.

Construction

The castle can be made from individual

brick A brick is a type of block used to build walls, pavements and other elements in masonry construction. Properly, the term ''brick'' denotes a block composed of dried clay, but is now also used informally to denote other chemically cured cons ...

s; usually with interlocking chevron edges to prevent "shine paths" of direct radiation through the gaps. They can also be made from lead produced in bespoke shapes by machining or casting. Such an example would be the annular ring castle commonly used for shielding scintillation counters. A typical lead brick weighs about ten

kilograms The kilogram (also kilogramme) is the unit of mass in the International System of Units (SI), having the unit symbol kg. It is a widely used measure in science, engineering and commerce worldwide, and is often simply called a kilo colloquially ...

. 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 up on a floor designed to carry the weight, or in the basement of a building built on a

concrete Concrete is a composite material composed of fine and coarse aggregate bonded together with a fluid cement (cement paste) that hardens (cures) over time. Concrete is the second-most-used substance in the world after water, and is the most wi ...

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

Notes and references

External links

{{Commons category, Lead radiation shielding
Lead castle pictures
Lead Nuclear physics Nuclear safety and security Radiation protection