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General Chemistry Principles, Patterns, and Applications, 2011

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Data source: T. R. Engl<strong>and</strong> <strong>and</strong> B. F. Rider, Los Alamos National Laboratory, LA-UR-94-3106,<br />

ENDF-349 (1993).<br />

Synthesis of Transuranium Elements<br />

Uranium (Z = 92) is the heaviest naturally occurring element. Consequently, all the elements with Z > 92,<br />

the transuranium elements, are artificial <strong>and</strong> have been prepared by bombarding suitable target nuclei<br />

with smaller particles. The first of the transuranium elements to be prepared was neptunium (Z = 93),<br />

which was synthesized in 1940 by bombarding a 238 U target with neutrons. As shown in Equation 20.21,<br />

this reaction occurs in two steps. Initially, a neutron combines with a 238 U nucleus to form 239 U, which is<br />

unstable <strong>and</strong> undergoes beta decay to produce 239 Np:<br />

Equation 20.21<br />

U92238 + n01®U92239 ® N93239 p + b -10<br />

Subsequent beta decay of 239 Np produces the second transuranium element, plutonium (Z = 94):<br />

Equation 20.22<br />

N93239 p ® P94239u + b -10<br />

Bombarding the target with more massive nuclei creates elements that have atomic numbers significantly<br />

greater than that of the target nucleus (Table 20.2 "Some Reactions Used to Synthesize Transuranium<br />

Elements"). Such techniques have resulted in the creation of the superheavy elements 114 <strong>and</strong> 116, both of<br />

which lie in or near the “isl<strong>and</strong> of stability” discussed in Section 20.1 "The Components of the Nucleus".<br />

Table 20.2 Some Reactions Used to Synthesize Transuranium Elements<br />

P94239u +a24 ® C96242m + n01<br />

P94239u +a24 ® A95241m + p11+ n01<br />

C96242m +a24 ® B97243k + p11+ 2n01<br />

E99253s +a24 ® M101256d + n01<br />

U92238 + C612 ® C98246 f + 4n01<br />

C98252 f + B510 ® L103256r + 6n01<br />

A device called a particle accelerator is used to accelerate positively charged particles to the speeds<br />

needed to overcome the electrostatic repulsions between them <strong>and</strong> the target nuclei by using electrical<br />

<strong>and</strong> magnetic fields. Operationally, the simplest particle accelerator is the linear accelerator (Figure 20.9<br />

Saylor URL: http://www.saylor.org/books<br />

Saylor.org<br />

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