Question 29.9: Synthetic Elements Goal Construct equations for a series of ...

(a) Identify the isotope produced by the reaction of a neutron with a target of { }_{92}^{238} \mathrm{U}, with production of a gamma ray.

Write an equation for the reaction in terms of the unknown isotope:

{ }_{0}^{1} \mathrm{n}+{ }_{92}^{238} \mathrm{U} \rightarrow{ }_{Z}^{A} \mathrm{X}+\gamma

Write and solve equations for the atomic mass and atomic number:

A=1+238=239 ; \quad Z=0+92=92

Identify the isotope:

{ }_{Z}^{A} \mathrm{X}={ }_{92}^{239} \mathrm{U}

(b) Write the equation for the beta decay of { }_{92}^{239} \mathrm{U}, identifying the resulting isotope. Write an equation for the decay of { }_{92}^{239} \mathrm{U} by beta emission in terms of the unknown isotope:

{ }_{92}^{239} \mathrm{U} \rightarrow{ }_{Z}^{A} \mathrm{Y}+\mathrm{e}^{-}+\bar{\nu}

Write and solve equations for the atomic mass and charge conservation (the electron counts as -1 on the right):

A=239 ; \quad 92=Z-1 \rightarrow Z=93

Identify the isotope:

{ }_{Z}^{A} \mathrm{Y}={ }_{93}^{239} \mathrm{~Np} \text { (neptunium) }

Remarks The interesting feature of these reactions is the fact that uranium is the element with the greatest number of protons (92) which exists in nature in any appreciable amount. The reactions in parts (a) and (b) do occur occasionally in nature; hence, minute traces of neptunium and plutonium are present. In 1940, however, researchers bombarded uranium with neutrons to produce plutonium and neptunium. These two elements were the first elements made in the laboratory. Since then, the list of synthetic elements has been extended to include those up to atomic number 112. Recently, elements 113 and 115 have been observed, but as of this writing, their existence has not yet been confirmed.