Section 24-1

Section 24.1 Nuclear Radiation

• Summarize the events that led to understanding radiation.

• Identify alpha, beta, and gamma radiations in terms of composition and key properties.

Section 24-1

Section 24.1 Nuclear Radiation (cont.)

radioisotope

X ray

penetrating power

Under certain conditions, some nuclei can emit alpha, beta, or gamma radiation.

The Discovery of Radiation• Nuclear reactions are different from other types of

reactions.

• Minerals that emit light after being exposed to sunlight, a phenomenon called phosphorescence.

• Nuclear chemistry is concerned with the structure of atomic nuclei and the changes they undergo.

• Marie Curie and her husband Pierre isolated the first radioactive materials.

• Radioactivity : The process by which materials give off spontaneous emissions “rays” without exposed to the light.

Section 24-1

The Discovery of Radiation (cont.)

Section 24-1

Types of Radiation• Isotopes are atoms of the same element that have

different numbers of neutrons.

• Isotopes of atoms with unstable nuclei are called radioisotopes.

• Unstable nuclei emit radiation to attain more stable atomic configurations in a process called radioactive decay.

• The three most common types of radiation are alpha, beta, and gamma.

Section 24-1

Types of Radiation (cont.)

Section 24-1

Types of Radiation (cont.)

• Alpha particles have the same composition as a helium nucleus 2

4He—two protons and two neutrons.

• Because of the protons, alpha particles have a 2+ charge.

• Alpha radiation consists of a stream of particles.

Section 24-1

Types of Radiation (cont.)

• Alpha radiation is not very penetrating—a single sheet of paper will stop an alpha particle.

• A radium-226 nucleus undergoes alpha decay to form radon-222 and an alpha particle

What is the number of protons and neutrons in radium-226 and radon-222?

Radium-226: 88 protons, 138 neutrons; Radon-222: 86 protons, 136 neutrons

Section 24-1

Types of Radiation (cont.)

• Beta particles are very fast-moving electrons emitted when a neutron is converted to a proton.

n→ p + β

• Beta particles have insignificant mass (almost zero) and a 1– charge.

Section 24-1

Types of Radiation (cont.)

• Beta radiation is a stream of fast moving particles with greater penetrating power—a thin sheet of foil will stop them.

• An iodine-131 nucleus undergoes beta decay to form xenon-131 and a beta particle

• How does beta decay affect the mass number of the decaying nucleus?

• The mass number does not change .

Section 24-1

Types of Radiation (cont.)

• Gamma rays are high-energy electromagnetic radiation.

• Gamma rays (short wavelength) are photons, which are high-energy

• Gamma rays have no mass or charge so the 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.

• X rays are a form of high-energy electromagnetic radiation emitted from certain materials in an excited state.

Q: Compare and contrast X-rays and gamma rays.

X-rays are emitted from materials that are in an excited state. Gamma rays are produced by radioactive sources.

Section 24-1

Types of Radiation (cont.)

• The ability of radiation to pass through matter is called its penetrating power.

• Gamma rays are highly penetrating because they have no charge and no mass.

A. A

B. B

C. C

D. D

Section 24-1

Section 24.1 Assessment

Why do radioisotopes emit radiation?

A. to balance charges in the nucleus

B. to release energy

C. to attain more stable atomic configurations

D. to gain energy

A. A

B. B

C. C

D. D

Section 24-1

Section 24.1 Assessment

X rays are most similar to what type of nuclear emissions?

A. gamma rays

B. alpha particles

C. beta particles

D. delta waves

• Q1: List the different types of radiation and their charges.

• alpha (2+), beta (1-), and gamma (0)

• Q2: Compare the subatomic particles involved in nuclear and chemical reactions.

• Protons, electrons, and neutrons can be involved in nuclear change; only electrons are involved in chemical change.

• Q3: Explain how you know whether the reaction is chemical or nuclear when an atom undergoes a reaction and attains a more-stable form.

• If the new, more stable form of the atom has an identity different from the original atom, a nuclear process has occurred.

A. A

B. B

C. C

D. D

STP 1

Which statement is NOT true of beta particles?

A. They have the same mass as an electron.

B. They have a charge of 1+.

C. They are less penetrating than alpha particles.

D. They are represented by 0-1β.

End of section 24.1