Page 9 - Academic Press Encyclopedia of Physical Science and Technology 3rd InOrganic Chemistry

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Encyclopedia of Physical Science and Technology EN001F-11 May 7, 2001 12:19

Actinide Elements 217

TABLE II Important Isotopes of the Actinide Elements
Atomic number Element Isotope Half-life Mode of decay
−
89 Actinium 227 Ac 21.7 years β (0.986), α(0.014), γ
228 −
Ac 6.15 h β
90 Thorium 232 Th 1.405 · 10 10 years α,
91 Protactinium 231 Pa 32760 years α, γ
234 −
Pa 6.70 h β
8
92 Uranium 235 U 7.038 · 10 years α
238 9
U 4.468 · 10 years α
6
93 Neptunium 237 Np 2.144 · 10 years α
94 Plutonium 238 Pu 87.7 years α
4
239 Pu 2.411 · 10 years α
5
242 Pu 3.733 · 10 years α
7
244 Pu 8.08 · 10 years α(0.999), sf(0.001)
95 Americium 241 Am 432.2 years α, γ
243 Am 7370 years α
96 Curium 242 Cm 162.8 days α
244 Cm 18.10 years α
248 Cm 3.40 · 10 years α(0.916), sf(0.084)
5
97 Berkelium 247 Bk 1380 years α(<100%)
249 Bk 320 days β (0.99999), α(0.00001)
−
98 Californium 249 Cf 351 years α
251 Cf 898 years α
252 Cf 2.645 year α(0.969), sf(0.031)
99 Einsteinium 252 Es 471.7 days α(0.76, ε(0.24)
253
Es 20.47 days α
254
Es 275.7 days α
100 Fermium 252 Fm 25.39 h α(0.99998), sf(0.00002)
255
Fm 20.07 h α
256
Fm 157.6 min sf(0.919), α(0.081)
101 Mendelevium 255 Md 27 min ε(0.92), α(0.08)
256
Md 78.1 min ε(0.907), α(0.093)
102 Nobelium 259 No 58 min α(0.75), ε(0.25)
103 Lawrencium 260 Lr 3.0 min α(0.75), ε(0.25)

◦
be produced by reducing AcF 3 with lithium at 1200 C. acid treatment dissolves the thorium phosphate present,
Small amounts of actinium can be obtained from residues while the basic process converts the phosphates to insol-
of uranium processing. Gram amounts of 227 Ac has been uble hydroxides. The separation of thorium from the ura-
produced synthetically at Mol, Belgium, by neutron irra- nium and rare-earth phosphates after the acid process can
diation of 226 Ra [Eq. (9)]: be carried out by selective precipitation of the thorium and
rare earth phosphates and then by using a solvent extrac-
−β −
226 1 227 227 tion process to remove the thorium. When the alkali open-
88 Ra + n → 88 Ra + γ −−−→ 91 Ac. (9)
0
42.2 min
ing method is used, the insoluble hydroxides are dissolved
Both thorium and uranium occur to a significant extent in in nitric acid and the thorium and uranium(VI) species are
nature, and industrial processes have been developed for extracted, leaving the lanthanides in the aqueous phase.
the production of these elements. The thorium and uranium can then be separated by further
Thorium is produced commercially from monazite solvent extraction.
sands. After mining, the monazite sands are concentrated Thorium metal can be produced in several ways. In
magnetically and then treated with either hot, concentrated the most common process, thorium oxide is reduced with
sulfuric acid or hot, concentrated sodium hydroxide. The calcium [Eq. (10)]: