Chapter 9

Chapter 9 Nuclear Chemistry

9-1 Introduction

  • Focus on the study of nuclear reactions and the properties of radioactive materials.

9-2 What Is Radioactivity?

Radioactive Materials

  • Nuclear decay (or radioactive decay): Process where an unstable atomic nucleus loses energy.

  • Nuclear radiation: Energy emitted from a nucleus during radioactive decay.

  • Radioactive material: Substances that contain unstable nuclei.

9-3 Types of Nuclear Radiation

  • Alpha particles (α):

    • Helium nuclei containing 2 protons and 2 neutrons with a charge of +2.

  • Beta particles (β):

    • Electrons with a charge of -1.

  • Gamma rays (γ):

    • High-energy electromagnetic radiation with no mass or charge.

Behavior of Nuclear Radiation

  • Alpha particles are heavier and deflected less than beta particles when passed through charged plates.

  • Gamma rays, being neutral, pass undeflected.

9-4 Electromagnetic Radiation

  • Gamma rays are part of electromagnetic spectrum, which includes X-rays, visible light, and radio waves.

  • Wavelength (λ): Distance from one wave crest to the next.

  • Frequency (ν): Number of wave crests passing a point in one second.

  • Relationship between wavelength and frequency: As frequency increases, wavelength decreases.

  • Higher frequency correlates with higher energy.

9-5 Radioactive Materials

  • Radioactive materials emit radiation and are derived from the nucleus, not the electron cloud.

9-6 What Happens When a Nucleus Emits Radioactivity?

Isotopes

  • Atoms with identical proton numbers but different neutron counts.

  • Stable isotopes: Do not emit radioactivity (e.g., 264 of the 300 known isotopes).

  • Unstable isotopes: Radioactive and decay over time.

9-7 Stability of Nuclei

  • Lighter elements: Stable isotopes usually have equal protons and neutrons.

  • Heavier elements require more neutrons than protons for stability.

  • Nuclei undergoing nuclear reactions to balance proton-neutron ratios.

9-8 Types of Nuclear Decay

  • Beta Emission:

    • Unstable nuclei convert neutrons to protons to stabilize.

  • Alpha Emission:

    • Emission of a helium nucleus reduces atomic number by 2 and mass number by 4.

  • Gamma Emission:

    • Accompanies alpha and beta decay, with no change in atomic structure.

9-9 Nuclear Half-Life

  • Half-life (t1/2): Time it takes for half a sample of a radioactive isotope to decay.

  • Example with iodine-131:

    • Half-lives measured over days indicate decay rates (8 days for first half-life).

9-10 Radiation Dosimetry and Human Health

  • Alpha particles: High tissue damage but low penetration (not harmful unless ingested).

  • Beta particles: Moderately damaging and penetrate deeper.

  • Gamma rays: Highly penetrating and the most dangerous.

9-11 Effects of Radiation Doses

  • 25 rem: noticeable white blood cell reduction.

  • 100 rem: radiation sickness symptoms.

  • 400 rem: 50% fatality within one month.

  • 600 rem: almost all fatal within a month.

  • High doses necessary for sterilization of bacteria.

9-12 Nuclear Medicine

Medical Imaging

  • Uses radioactive isotopes to form images of targeted tissues.

  • Key requirements: radioactive element, detection method, and imaging computational tools.

Radiation Therapy

  • Utilizes isotopes for the destruction of diseased cells, particularly effective on rapidly dividing cells.

  • Cobalt-60 is commonly used for targeted radiation therapy.

9-13 Nuclear Fusion and Fission

Nuclear Fusion

  • Combining light nuclei (e.g., hydrogen) to form heavier nuclei with energy release.

  • Fusion in hydrogen bombs is uncontrolled, but controlled fusion could solve energy problems.

Nuclear Fission

  • Splitting of heavy nuclei (e.g., uranium-235) releases significant energy.

  • Initiated by neutron collision, causing a chain reaction.

  • Controlled in nuclear power plants using materials like boron to absorb neutrons and manage fission reactions, generating electricity.