Uranium

Symbol UAtomic number 92
Atomic mass
238.029
 Thermal conductivity
0.276
Atomic radius
...
 Covalent radius
1.42
Density
18.7
 Atomic volume
12.59
Melting point
1405
 Oxidation states
6,5,4,3
Boiling point
4091
 Stable isotopes
2
Heat of vapor.
477.0
 Electronegativity
1.38
Heat of fusion
8.52
 First ionization
6.05
Specific heat
0.12
 Electrical conduct.
...
Electron configuration
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Uranium

Uranium is the rarest metal of the chromium group. It was not valued until the discovery in 1942 that it was capable of nuclear fission, yielding an enormous amount of energy. For energy use, uranium is usually purified in the form of uranium oxide U3O8, commonly called yellowcake. This image of uranium oxide is from Wikipedia.

 

Uranium is usually found in the ores pitchblende (U3O8) and carnotite (K2U2V2O12.3H2O). It is also found in the minerals Becquerelite, euxenite and Boltwoodite. Uranium appears in the phosphate minerals meta-autunite and metatorbernite. Uranium appears with lead in curite and kasolite, both of which exhibit orange coloration which might be the source of color in radioactive orange fiestaware dishes. It appears with vanadium and lead in Francevillite.

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Uranium Nuclear Data

Z
A
Atomic
Mass (u)
Nuclear
Mass(GeV/c2
Binding
Energy(MeV)
Spin
Natural
Abund.
Half-life
Decay
Q
MeV
92
226
226.029170
210.4995
1725.0
0
...
0.5s
a
7.56
92
231
231.036270
215.1636
1758.7
5/2
...
4.2d
EC
0.36
92
232
232.037130
216.0959
1766.0
0
...
68.9d
a
5.41
92
233
233.039628
217.0298
1771.8
5/2
...
0.159My
a
4.91
92
234
234.040947
217.9625
1778.6
0
5.5x10-5
0.245My
a
4.86
92
235
235.043924
218.8968
1783.9
7/2
0.0072
0.704Gy
a
4.68
92
236
236.045563
219.8298
1790.4
0
...
23.4My
a
4.57
92
238
238.050785
221.6977
1801.7
0
0.99275
4.46Gy
a
4.27
92
239
239.054290
222.6324
1806.5
5/2
...
23.54m
b-
1.26

Uranium plays a major role in the natural radioactive series on the earth. 235U is the progenitor of the uranium-235 series, 238U the progenitor of the uranium-238 series, and 233U is a member of the neptunium-237 series. Uranium-235 is the most important isotope for nuclear fission.

From Evans: "238U does show a half-period of about 1016 years for spontaneous fission, or about 25 fissions per hour in 1 gram of 238U. The probability of a decay is about 107 times as great." The half-life for spontaneous fission for 235U is about 1.8 x 1017 years compared to its a half-life of 7 x 108 years.

Uranium is a key to the uranium-lead dating processes in geology, where the ratio found in rock from the Earth, moon and meteorites is 238U/235U =137.88 (Dalrymple, Ch. 3). This ratio is use for developing the equations for Pb-Pb isochrons.

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