Nuclear Chemistry

Berea Arts and Science High School
Nuclear Chemistry Notes and Problem Set

Notes
Radioactive decay – the process in which a nucleus spontaneously disintegrates, giving
off radiation

Nuclear bombardment reaction – a nuclear reaction in which a nucleus is bombarded, or
struck, by another nucleus or by a nuclear particle

Types of Radioactive Decay
a. Alpha emission – emission of a 42He nucleus, or alpha particle, from an unstable
nucleus. An example is the radioactive decay of radium-22, written as

22688Ra 22286Rn + 42He

The product nucleus has an atomic number that is two less, and a mass number
that is four less, than that of the original nucleus.

b. Beta emission – emission of a high-speed electron from an unstable nucleus. Beta
emission is equivalent to the conversion of a neutron to a proton.

10n 11p + 0-1e

An example of beta emission is the radioactive decay of carbon-14.

146C 147N + 0-1e

the product nucleus has an atomic number that is one more than that of the
original nucleus. The mass number remains the same.

c. Positron emission – emission of a positron from an unstable nucleus. Positron emission
is equivalent to the conversion of a proton to a neutron.

11p 10n + 01e
d. Electron capture – the decay of an unstable nucleus by capturing, or picking up, an
electron from an inner orbital of an atom. In effect, a proton is changed to a neutron as in positron emission

11p + 0-1e 10n

e. Gamma emission – emission from an excited nucleus of a gamma photon,
corresponding to radiation with a wavelength of about 10-12 m. in many cases, radioactive results in a product nucleus that is in an excited state. Often, gamma emission occurs very quickly after radioactive decay

Metastable nucleus – a nucleus in an excited state with a lifetime of at least one
nanosecond (10-9 s). In time, the metastable nucleus decays by gamma emission. An example is metastable technetium-99, denoted 99m43Tc, which is used in medical diagnosis.

99m43Tc 9943Tc + 00

he product nucleus is simply a lower-energy state of the original nucleus, so there is no change of atomic number or mass number.

Radioactive decay series – a sequence in which one radioactive nucleus decays to a
second, which then decays to a third, and so forth. Eventually, a stable nucleus is reached. For the natural radioactive decay series, this stable nucleus is an isotope of lead.

Particle accelerator – a device used to accelerate electrons, protons, and alpha particles
and other ions to very high speeds.

Cyclotron – a type of particle accelerator consisting of two hollow, semicircular metal
electrodes, called dees (because the shape of a dee resembles the letter D) in which charged particles are accelerated by stages to a higher and higher kinetic energies.

Nuclear force – a strong force of attraction between nucleons that acts only at very short
distances (about 10-15 m)

Problem Set
1. Of the following nuclides, two are radioactive. Which are radioactive and which is
stable?
a. 11850Sn b. 7633As c. 22789Ac

2. Potassium-40 is a naturally occurring radioactive isotope. It decays to calcium-40 by
beta emission. When a potassium-40 nucleus decays by beta emission, it emits one beta particle and gives a calcium-40 nucleus. Write the nuclear equation for this decay.

3. Plutonium-239 decays by alpha emission, with each nucleus emitting one alpha
particle. What is the other product of this decay?

4. Cobalt-60, used in cancer therapy, decays by beta and gamma emission. The decay
constant is 4.18 x 10-9/s. what is the half-life in years?

5. A nuclear power plant emits into the atmosphere a very small amount of krypton-85, a
radioactive isotope with a half-life of 10.76 y. What fraction of this krypton-85 remains after 25.0 y?