1. Lesson 1
Nuclear Radiation

2. Focus Question
How was radioactivity discovered?

3. New Vocabulary
radioisotope
X-ray
penetrating power

4. Review Vocabulary
element: a pure substance that cannot be broken down into simpler substances by physical or chemical means

5. The Discovery of Radioactivity
Nuclear chemistry is concerned with the structure of atomic nuclei and the changes they undergo.
Table 1 Comparison of Chemical and Nuclear Reactions
Chemical Reactions
Nuclear Reactions
Occur when bonds are broken and formed
Involve only valence electrons
Associated with small energy changes
Atoms keep the same identity although they might gain, lose, or share electrons, and form new substances
Temperature, pressure, concentration, and catalysts affect reaction rates
Occur when nuclei combine, split, and emit radiation
Can involve protons, neutrons, and electrons
Associated with large energy changes
Atoms of one element are often converted into atoms of another element
Temperature, pressure, and catalysts do not normally affect reaction rates

6. The Discovery of Radioactivity
Wilhelm Roentgen discovered X-rays in 1895.
Henri Becquerel, Marie Curie, and Pierre Curie pioneered the fields of radioactivity and nuclear chemistry.
In 1898, the Curies identified two new elements, polonium and radium, on the basis of their radioactivity.

7. Types of Radiation
Isotopes of atoms with unstable nuclei are called radioisotopes.
These unstable nuclei emit radiation to attain more stable atomic configurations in a process called radioactive decay.

8. Types of Radiation
During radioactive decay, unstable nuclei release energy by emitting radiation.
The three most common types are alpha (α), beta (β), and gamma (γ).

9. Types of Radiation
Ernest Rutherford identified alpha, beta, and gamma radiation when studying the effects of an electric field on the emissions from a radioactive source.

10. Types of Radiation
An alpha particle (α) has the same composition as a helium nucleus—two protons and two neutrons.
The charge of an alpha particle is 2+ due to the presence of the two protons.
Alpha radiation consists of a stream of alpha particles.
Alpha particles are not very penetrating; a single sheet of paper stops alpha particles.

11. Types of Radiation
A radium-226 nucleus undergoes alpha decay to form radon-222 and an alpha particle.

12. Types of Radiation
A beta particle is a very fast-moving electron that is emitted when a neutron in an unstable nucleus converts into a proton.
Beta particles are represented by the symbol β or e-. They have a 1- charge.
Beta radiation consists of a stream of fast-moving electrons.
A thin sheet of metal foil is required to stop beta particles.

13. Types of Radiation
An iodine-131 nucleus undergoes beta decay to form xenon-131 and a beta particle.

14. Types of Radiation
Gamma rays are high-energy electromagnetic radiation denoted by the symbol γ.
Emission of gamma rays does not change the atomic number or mass number of a nucleus.
Gamma rays almost always accompany alpha and beta radiation. They account for most of the energy loss as a nucleus decays.
Some, but not all, gamma rays are stopped by a thick layer of concrete or lead.

15. Types of Radiation
X-rays are high-energy electromagnetic radiation that are not produced by radioactive sources.
Their energy is lower than that of gamma rays.
X-rays are emitted when inner electrons are knocked out, and electrons from higher energy levels drop down to fill the vacancy.

16. Types of Radiation
The ability of radiation to pass through matter is called penetrating power.
Penetrating power is quantified as the depth of water that stops 50 percent of incoming radiation.
Gamma rays have the highest penetrating power because they have no charge or mass.

17. Quiz 1.
Who identified two new elements, polonium and radium, on the basis of their radioactivity?
Wilhelm Roentgen A
Marie and Pierre Curie B
CORRECT
Henri Becquerel C
Ernest Rutherford D

18. Quiz 2.
Which name best identifies isotopes of atoms with unstable nuclei?
radioisotopes A
CORRECT
alpha particles B
beta particles C
gamma rays D

19. Quiz 3. Which is true of an alpha particle?
It has the same composition as a helium nucleus. A
CORRECT
It is a fast-moving electron. B
It has no mass or charge. C
It is denoted by the symbol γ. D

20. Quiz 4.
In beta decay, the mass number of the product nucleus is the same as that of the original nucleus. What happens to the atomic number?
It increases by 2. A
It decreases by 2. B
It increases by 1. C
CORRECT
It decreases by 1. D

21. Quiz 5. Which type of radiation has the greatest penetrating power?
X-ray radiation A
beta radiation C
alpha radiation B
gamma radiation D
CORRECT