Nuclear ChemistryChapter 25

Marie Curie was a Polish scientist whose research led to many discoveries about radiation and radioactive elements. In 1934 she died from leukemia caused by her long-term exposure to radiation. You will learn about the various types of radiation and their effects.

Nuclear Radiation25.1

Marie Curie (1867-1934) and Pierre Curie (1859-1906) were able to show that rays emitted by uranium atoms caused fogging in photographic plates. Marie Curie named the process by which materials give

off such rays radioactivity. The penetrating rays and particles emitted by a

radioactive source are called radiation.

Radioactivity25.1

Nuclear reactions differ from chemical reactions in a number of important ways. In chemical reactions, atoms tend to attain stable

electron configurations by losing or sharing electrons. In nuclear reactions, the nuclei of unstable isotopes,

called radioisotopes, gain stability by undergoing changes.

In the periodic table, radioactive elements have mass numbers in parentheses. Reference table N

Radioactivity25.1

◦ An unstable nucleus releases energy by emitting radiation during the process of radioactive decay.

Radioactivity25.1

Types of Radiation◦ What are the three main types of nuclear

radiation?

Types of Radiation25.1

The three main types of nuclear radiation are alpha radiation, beta radiation, and gamma radiation. Reference table O

Types of Radiation25.1

◦ Alpha RadiationAlpha radiation consists of helium nuclei that have been emitted from a radioactive source. These emitted particles, called alpha particles, contain two protons and two neutrons and have a double positive charge.

Note: In a nuclear decay equation, mass and charge are conserved!

Types of Radiation25.1

Types of Radiation25.1

◦ Beta Radiation An electron resulting from the breaking apart of a

neutron in an atom is called a beta particle.

Types of Radiation25.1

Carbon-14 emits a beta particle as it undergoes radioactive decay to form nitrogen-14.

Types of Radiation25.1

Types of Radiation25.1

◦ Gamma Radiation A high-energy photon emitted by a radioisotope is

called a gamma ray. The high-energy photons are electromagnetic radiation.

Types of Radiation25.1

Alpha particles are the least penetrating. Gamma rays are the most penetrating.

Types of Radiation25.1

Types of Radiation25.1

Radon-222 is a radioactive isotope that is present naturally in the soil in some areas. It has a constant rate of decay. You will learn about decay rates of radioactive substances.

Nuclear Transformations25.2

Radioactive substances decay at a constant rate regardless of factors such as temperature and concentration.

Radioactive decay is a random event. Decay continues until a stable isotope is

formed.◦ Some radioisotopes have a long decay series.

Half-Life

Half-Life25.2

Stable Isotope

The time it takes for half the atoms in a sample to decay is called the half-life.

Each isotope has its own unique half-life. The shorter the half-life, the less stable it is.

Reference table N

Half-Life

If a 100 g sample has a half-life of 5 days:◦ After 5 days ½ (50g) will remain undecayed◦ After 10 days ¼ (25g) will remain undecayed◦ After 15 days 1/8 (12.5g) will remain undecayed◦ After 20 days 1/16 (6.25g) will remain undecayed◦ And so on…

Half-Life

The ratio of Carbon-14 to stable carbon in the remains of an organism changes in a predictable way that enables the archaeologist to obtain an estimate of its age.

Half-Life25.2

Radioactive decay is measured with a Geiger counter.◦ A Geiger counter records individual decay events.

Graphing decay allows determination of the half-life.

Graphing Half-Life

Half-Life25.2

Transuranium elements are synthesized in nuclear reactors and nuclear accelerators.

Transmutation Reactions

The conversion of an atom of one element to an atom of another element is called transmutation.

What are two ways that transmutation can occur?

Transmutation Reactions

Transmutation can occur naturally by radioactive decay.◦ a single nucleus undergoes decay

Transmutation can also occur artificially when particles bombard the nucleus of an atom.◦ at least two reactants produce the target material

Transmutation Reactions

A nucleus is bombarded with high-energy particles to bring about a change.

Two types:◦ Bombarding with charged particles: protons or

alpha particles. Particle accelerators use magnetic or electrostatic

fields to accelerate particles towards the target. Cern video

◦ Bombarding with neutrons. Neutrons are obtained as by-products of nuclear

reactors.

Artificial Transmutation

The first artificial transmutation reaction involved bombarding nitrogen gas with alpha particles.

Transmutation Reactions

The elements in the periodic table with atomic numbers above 92, the atomic number of uranium, are called the transuranium elements.◦ All transuranium elements undergo

transmutation.

◦ None of the transuranium elements occur in nature, and all of them are radioactive.

Transmutation Reactions

The sun is not actually burning. If the energy given off by the sun were the product of a combustion reaction, the sun would have burned out approximately 2000 years after it was formed, long before today. You will learn how energy is produced in the sun.

Fission and Fusion of Atomic Nuclei

25.3

Nuclear Fission◦ What happens in a nuclear chain reaction?

Nuclear Fission25.3

When the nuclei of certain isotopes are bombarded with neutrons, they undergo fission, the splitting of a nucleus into smaller fragments.

Nuclear Fission25.3

◦ In a chain reaction, some of the neutrons produced react with other fissionable atoms, producing more neutrons which react with still more fissionable atoms.

Nuclear Fission25.3

Nuclear Fission

Nuclear Fission25.3

Nuclear Fission25.3

A Nuclear Power Plant

Nuclear Waste◦ Why are spent fuel rods from a nuclear reaction

stored in water?

Nuclear Waste25.3

Water cools the spent rods, and also acts as a radiation shield to reduce the radiation levels.

Nuclear Waste25.3

Nuclear Fusion◦ How do fission reactions and fusion reactions

differ?

Nuclear Fusion25.3

Fusion occurs when nuclei combine to produce a nucleus of greater mass. In solar fusion, hydrogen nuclei (protons) fuse to make helium nuclei and two positrons.

Nuclear Fusion25.3

◦ Fusion reactions, in which small nuclei combine, release much more energy than fission reactions, in which large nuclei split.

Nuclear Fusion25.3

The use of controlled fusion as an energy source on Earth is appealing. The potential fuels are inexpensive and readily available. The problems with fusion lie in achieving the high

temperatures necessary to start the reaction and in containing the reaction once it has started.

Nuclear Fusion25.3

In a smoke detector, radiation from the Americum nuclei ionizes the nitrogen and oxygen in smoke-free air, allowing a current to flow. When smoke particles get in the way, a drop in current is detected by an electronic circuit, causing it to sound an alarm. You will learn about some of the other practical uses of radiation.

Radiation in Your Life25.4

C-14 is used to date fossils.

U-238 is used to date rocks.

Radioactive Dating

Radioisotopes are used to trace chemical pathways in biological systems.

Chemical Tracers

Radioisotopes are used to determine minute thicknesses such as plastic wrap and aluminum foil.

Gamma radiation is used to irradiate foods to kill bacteria and make the foods last longer.

Industrial Applications

Radioisotopes with short half-lives that are quickly eliminated from the body are used as tracers in medical diagnoses and treatments.◦ I-131 is used to detect and treat thyroid disorders.◦ Co-60 is used in cancer treatments.◦ Tc-99 is used to detect tumors.

Medical Applications

This scanned image of a thyroid gland shows where radioactive iodine-131 has been absorbed.

Using Radiation25.4

In medical treatments radiation can destroy normal cells as well as cancerous cells.

Radiation leaking from a nuclear power plant can cause mutations that could be inherited.

Spent fuel rods are a disposal concern. They are still radioactive and potentially dangerous.

Radiation Risks