CK-12-Chemistry Intermediate

http://www.ck12.org Chapter 24. Nuclear Chemistry

In the first step, uranium-238 decays by alpha emission to thorium-234 with a half-life of 4.5× 109 years. This
decreases its atomic number by two. The thorium-234 rapidly decays by beta emission to protactinium-234 (t 1
2

=

24.1 days). The atomic number increases by one. This continues for many more steps until eventually the series
ends with the formation of the stable isotope, lead-206.

Artificial Transmutation

As we have seen, transmutation occurs when atoms of one element spontaneously decay and are converted to
atoms of another element. Artificialtransmutationis the bombardment of stable nuclei with charged or uncharged
particles in order to cause a nuclear reaction. The bombarding particles can be protons, neutrons, alpha particles,
or larger atoms. Ernest Rutherford performed some of the earliest bombardments, including the bombardment of
nitrogen gas with alpha particles to produce the unstable fluorine-18 isotope.

14

7 N+

4

2 He→

18

9 F

Fluorine-18 quickly decays to the stable nuclide oxygen-17 by releasing a proton.

18

9 F→

17

8 O+

1

1 H

When beryllium-9 is bombarded with alpha particles, carbon-12 is produced with the release of a neutron.

9

4 Be+

4

2 He→

12

6 C+

1

0 n

This nuclear reaction contributed to the discovery of the neutron in 1932 by James Chadwick. A shorthand notation
for artificial transmutations can be used. The above reaction would be written as:

9

4 Be(ff,n)

12

6 C

The parent isotope is written first. In the parentheses is the bombarding particle followed by the ejected particle.
The daughter isotope is written after the parentheses.

Positively charged particles need to be accelerated to high speeds before colliding with a nucleus in order to
overcome the electrostatic repulsion. The necessary acceleration is provided by a combination of electric and
magnetic fields. Shown below (Figure24.8) is an aerial view of the Fermi National Accelerator Laboratory in
Illinois.

Transuranium Elements

Many, many radioisotopes that do not occur naturally have been generated by artificial transmutation. The elements
technetium and promethium have been produced, since these elements no longer occur in nature. All of their isotopes
are radioactive and have half-lives short enough that any amount of the elements that once existed have long since
disappeared through natural decay. Thetransuranium elementsare elements with atomic numbers greater than
92. All isotopes of these elements are radioactive and none occur naturally. Listed below (Table24.5) are the
transuranium elements up through meitnerium, and the reactions by which they were formed.

TABLE24.5:The Transuranium Elements

Atomic Number Name Symbol Preparation

93 Neptunium Np^23892 U+^10 n→^23993 Np+−^01 fi