Decay Chain Examples-Teacher Answer Key
Cesium (Cs)	Americium (Am)
Half-life:
241
95
Am

Half-life:
239
Np
Cesium-137 is an isotope of cesium that is
produced when uranium and plutonium
absorb neutrons and undergo fission (the
splitting of a nucleus into at least two other
nuclei and the release of a relatively large
amount of energy; used to generate
nuclear power).
Americium-241 is produced in the same
process as Cesium-137; it is an isotope of
americium that is used in ionizing smoke
detectors and nuclear gauges.
The number of years listed in the example is the half-life for each element. Half-life is the amount of
time it takes for approximately one-half of the radioactive atoms to decay.
Radioactive elements decay at different rates (e.g., cesium has a half-life of 30.17 years and americium-
241 has a half-life of 432.7 years).
1.	What forms of radiation are released when cesium (Cs) converts to barium (Ba)?
Beta particle and gamma rays.
2.	What change occurs in the atomic properties of cesium (Cs) when it converts to barium (Ba)?
Why?
The number of protons increases by one and cesium (55) becomes barium (56) because before
a beta particle is released a neutron changes into a proton and an electron. The proton stays in
the nucleus and the electron is ejected from the nucleus in the form of beta particles. The
release of a beta particle decreases the number of neutrons by one and increases the number of
protons by one.
3.	What form of radiation is released when americium (Am) converts to neptunium (Np)?
Alpha particle.
4.	What change occurs in the atomic properties of americium (Am) when it convertsto neptunium
(Np)? Why?
An alpha particle is made up of two protons (+2) and two neutrons from the atom's nucleus.
When the ratio of neutrons to protons in the nucleus is too low, certain atoms restore the
balance by emitting alpha particles. This reduces the number of protons by two, changing
americium (95) to neptunium (93).
c/EPA
United States
Environmental Protection
Agency
RadTown Radioactive Atom Activity Set	EPA 402-B-19-022
https://www.EPA.gov/RadTown/Activitv-6-Radioactive-Decav-Chain

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