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Decay product

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The decay chain from lead-212 down to lead-208, showing the intermediate decay products.

In nuclear physics, a decay product (also known as a daughter product, daughter isotope or daughter nuclide) is the remaining nuclide left over from radioactive decay. Radioactive decay often involves a sequence of steps (decay chain). For example, U-238 decays to Th-234 which decays to Pa-234 which decays, and so on, to Pb-206 (which is stable):

$\mbox{U-238} \rightarrow \overbrace{ \underbrace{\mbox{Th-234}}_{\mbox{daughter of U-238}} \rightarrow \underbrace{\mbox{Pa-234m}}_{\mbox{granddaughter of U-238}} \rightarrow \ldots \rightarrow \mbox{Pb-206} }^{\begin{array}{c} \mbox{decay products of U-238} \end{array}}$

In this example:

Th-234, Pa-234m,…,Pb-206 are the decay products of U-238.
Th-234 is the daughter of the parent U-238.
Pa-234m (234 metastable) is the granddaughter of U-238.

These might also be referred to as the daughter products of U-238.^[1]

Decay products are important in understanding radioactive decay and the management of radioactive waste.

For elements above lead in atomic number, the decay chain typically ends with an isotope of lead.

In many cases members of the decay chain are far more radioactive than the original nuclide. Thus, although uranium is not dangerously radioactive when pure, some pieces of naturally-occurring pitchblende are quite dangerous owing to their radium content. Similarly, thorium gas mantles are very slightly radioactive when new, but become far more radioactive after only a few months of storage.

Although it cannot be predicted whether any given atom of a radioactive substance will decay at any given time, the decay products of a radioactive substance are extremely predictable. Because of this, decay products are important to scientists in many fields who need to know the quantity or type of the parent product. Such studies are done to measure pollution levels (in and around nuclear facilities) and for other matters.

References

^ Glossary of Volume 7 (Depleted Uranium — authors: Naomi H. Harley, Ernest C. Foulkes, Lee H. Hilborne, Arlene Hudson, and C. Ross Anthony) of A review of the scientific literature as it pertains to gulf war illnesses.