Uranium-232 () is an
isotope of uranium
Uranium is a chemical element with the symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium is weak ...
. It has a half-life of around
69 years and is a side product in the
thorium cycle. It has been cited as an obstacle to
nuclear proliferation
Nuclear proliferation is the spread of nuclear weapons, fissionable material, and weapons-applicable nuclear technology and information to nations not recognized as " Nuclear Weapon States" by the Treaty on the Non-Proliferation of Nuclear Wea ...
using
233U as the
fissile
In nuclear engineering, fissile material is material capable of sustaining a nuclear fission chain reaction. By definition, fissile material can sustain a chain reaction with neutrons of thermal energy. The predominant neutron energy may be ty ...
material, because the intense
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 ...
emitted by
208Tl (a daughter of
232U, produced relatively quickly) makes the
233U contaminated with it more difficult to handle.
Production of
233U (through the neutron irradiation of
232Th) invariably produces small amounts of
232U as an impurity, because of parasitic (n,2n) reactions on
uranium-233
Uranium-233 (233U or U-233) is a fissile isotope of uranium that is bred from thorium-232 as part of the thorium fuel cycle. Uranium-233 was investigated for use in nuclear weapons and as a reactor fuel. It has been used successfully in expe ...
itself, or on
protactinium-233
Protactinium (91Pa) has no stable isotopes. The three naturally occurring isotopes allow a standard atomic weight to be given.
Thirty radioisotopes of protactinium have been characterized, with the most stable being 231Pa with a half-life of 32, ...
, or on
thorium-232
Thorium-232 () is the main naturally occurring isotope of thorium, with a relative abundance of 99.98%. It has a half life of 14 billion years, which makes it the longest-lived isotope of thorium. It decays by alpha decay to radium-228; its decay ...
:
:
232Th (n,γ)
233Th (β−)
233Pa (β−)
233U (n,2n)
232U
:
232Th (n,γ)
233Th (β−)
233Pa (n,2n)
232Pa (β−)
232U
:
232Th (n,2n)
231Th (β−)
231Pa (n,γ)
232Pa (β−)
232U
Another channel involves neutron capture reaction on small amounts of thorium-230, which is a tiny fraction of natural thorium present due to the decay of
uranium-238
Uranium-238 (238U or U-238) is the most common isotope of uranium found in nature, with a relative abundance of 99%. Unlike uranium-235, it is non-fissile, which means it cannot sustain a chain reaction in a thermal-neutron reactor. However, i ...
:
:
230Th (n,γ)
231Th (β−)
231Pa (n,γ)
232Pa (β−)
232U
The decay chain of
232U quickly yields strong gamma radiation emitters:
[Griffin, H. C. ''Natural Radioactive Decay Chains'', Chapter 13 of ''Handbook of Nuclear Chemistry'', Second Edition, Springer 2011, ]
:
232U (α, 68.9 years)
:
228Th (α, 1.9 year)
:
224Ra (α, 3.6 day, 0.24 MeV) (from this point onwards, the decay chain is identical to that of
232Th; thorium-232 is nevertheless much less dangerous because its extremely long half-life of about 14-15 billion years means that not as much of its dangerous daughters builds up)
:
220Rn (α, 55 s, 0.54 MeV)
:
216Po (α, 0.15 s)
:
212Pb (β−, 10.64 h)
:
212Bi (α, 61 min, 0.78 MeV)
:
208Tl (β−, 3 min, 2.6 MeV) (35.94% branching ratio)
:
208Pb (stable)
This makes manual handling in a glove box with only light shielding (as commonly done with plutonium) too hazardous, (except possibly in a short period immediately following chemical separation of the uranium from its decay products) and instead requiring remote manipulation for fuel fabrication.
Unusually for an isotope with even
mass number,
232U has a significant
neutron absorption
Neutron capture is a nuclear reaction in which an atomic nucleus and one or more neutrons collide and merge to form a heavier nucleus. Since neutrons have no electric charge, they can enter a nucleus more easily than positively charged protons, ...
cross section
Cross section may refer to:
* Cross section (geometry)
** Cross-sectional views in architecture & engineering 3D
*Cross section (geology)
* Cross section (electronics)
* Radar cross section, measure of detectability
* Cross section (physics)
**Abs ...
for
fission (
thermal neutron
The neutron detection temperature, also called the neutron energy, indicates a free neutron's kinetic energy, usually given in electron volts. The term ''temperature'' is used, since hot, thermal and cold neutrons are moderated in a medium wit ...
s ,
resonance integral ) as well as for
neutron capture
Neutron capture is a nuclear reaction in which an atomic nucleus and one or more neutrons collide and merge to form a heavier nucleus. Since neutrons have no electric charge, they can enter a nucleus more easily than positively charged protons, ...
(thermal , resonance integral ).
References
{{Isotopes of uranium
Isotopes of uranium
Actinides
Nuclear materials