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Thorium-232
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Thorium-232
Thorium-232 (232
Th) is the main naturally occurring isotope of thorium, with a relative abundance of 99.98%. It has a half-life of 14.0 billion years, which makes it the longest-lived isotope of thorium. It decays by alpha decay to radium-228; its decay chain terminates at stable lead-208.
Thorium-232 is a fertile material; it can capture a neutron to form thorium-233, which subsequently undergoes two successive beta decays to uranium-233, which is fissile. As such, it has been used in the thorium fuel cycle in nuclear reactors; various prototype thorium-fueled reactors have been designed. However, as of 2024, thorium fuel has not been widely adopted for commercial-scale nuclear power.
The half-life of thorium-232 (14 billion years) is more than three times the age of the Earth; thorium-232 therefore occurs in nature as a primordial nuclide. Other thorium isotopes occur in nature in much smaller quantities as intermediate products in the decay chains of uranium-238, uranium-235, and thorium-232.
Some minerals that contain thorium include apatite, sphene, zircon, allanite, monazite, pyrochlore, thorite, and xenotime.
Thorium-232 has a half-life of 14 billion years; it is itself an essentially pure alpha emitter with its first decay product radium-228. This is itself unstable; and leads to a decay chain known as the thorium series, which terminates at stable lead-208. The intermediates in the thorium-232 decay chain are all relatively short-lived; the longest-lived intermediate decay products are radium-228 and thorium-228, with half-lives of 5.75 years and 1.91 years, respectively. All others have half-lives under four days. There are no minor branches in this chain, and it proceeds as shown:
Or the same in tabular form:
Although thorium-232 mainly alpha-decays, it also undergoes spontaneous fission 1.1×10−9% of the time, for a partial half-life of 1.3×1021 years, the longest known for that mode. Double beta decay to uranium-232 is also theoretically possible, but has not been observed.
Thorium-232 is not fissile; it therefore cannot be used directly as fuel in nuclear reactors. However, 232
Th is fertile: it can capture a neutron to form 233
Th, which undergoes a beta decay with a half-life of 21.8 minutes to 233
Pa, then another with a half-life of 27 days to form fissile 233
U.
Hub AI
Thorium-232 AI simulator
(@Thorium-232_simulator)
Thorium-232
Thorium-232 (232
Th) is the main naturally occurring isotope of thorium, with a relative abundance of 99.98%. It has a half-life of 14.0 billion years, which makes it the longest-lived isotope of thorium. It decays by alpha decay to radium-228; its decay chain terminates at stable lead-208.
Thorium-232 is a fertile material; it can capture a neutron to form thorium-233, which subsequently undergoes two successive beta decays to uranium-233, which is fissile. As such, it has been used in the thorium fuel cycle in nuclear reactors; various prototype thorium-fueled reactors have been designed. However, as of 2024, thorium fuel has not been widely adopted for commercial-scale nuclear power.
The half-life of thorium-232 (14 billion years) is more than three times the age of the Earth; thorium-232 therefore occurs in nature as a primordial nuclide. Other thorium isotopes occur in nature in much smaller quantities as intermediate products in the decay chains of uranium-238, uranium-235, and thorium-232.
Some minerals that contain thorium include apatite, sphene, zircon, allanite, monazite, pyrochlore, thorite, and xenotime.
Thorium-232 has a half-life of 14 billion years; it is itself an essentially pure alpha emitter with its first decay product radium-228. This is itself unstable; and leads to a decay chain known as the thorium series, which terminates at stable lead-208. The intermediates in the thorium-232 decay chain are all relatively short-lived; the longest-lived intermediate decay products are radium-228 and thorium-228, with half-lives of 5.75 years and 1.91 years, respectively. All others have half-lives under four days. There are no minor branches in this chain, and it proceeds as shown:
Or the same in tabular form:
Although thorium-232 mainly alpha-decays, it also undergoes spontaneous fission 1.1×10−9% of the time, for a partial half-life of 1.3×1021 years, the longest known for that mode. Double beta decay to uranium-232 is also theoretically possible, but has not been observed.
Thorium-232 is not fissile; it therefore cannot be used directly as fuel in nuclear reactors. However, 232
Th is fertile: it can capture a neutron to form 233
Th, which undergoes a beta decay with a half-life of 21.8 minutes to 233
Pa, then another with a half-life of 27 days to form fissile 233
U.