Nuclear Chemistry Chapter 5

Chapter 5: Nuclear Chemistry

• Nuclear chemistry examines unstable nuclei that spontaneously emit particles and energy to become more stable.
• Most isotopes of elements with atomic numbers 19 or lower are stable.
• Elements 20 and higher typically have some radioactive isotopes due to strong proton repulsions.
• Radioactive isotopes are unstable nuclei that emit radiation.
• Radioisotopes can be one or more isotopes of an element and are identified by mass number (protons + neutrons).
• Examples of radioisotopes include Carbon-14 (used in archeological dating, mass #14, atomic #6).

Types of Radiation

• Alpha (α) particles: identical to a helium nucleus (He-4), have 2 protons and 2 neutrons, +2 charge, low energy, stopped by paper or clothing.
• Beta (β) particles: high-energy electrons, -1 charge, mass #0, stopped by heavy clothing or lab coats, and aluminum
• Positrons (β+): high-energy particles, identical to electrons but with a +1 charge, mass #0, stopped by heavy clothing, and aluminum.
• Gamma (γ) rays: pure energy, no mass or charge, very high-energy radiation, penetrates thick materials like concrete or lead.

Radiation Protection

• Alpha particles require paper and clothing.
• Beta particles require lab coats or gloves.
• Gamma rays require lead or thick concrete.
• Limiting time near a radioactive source.
• Increasing distance from the source.
• Shielding material varies in effectiveness based on the type of radiation.

Nuclear Reactions

• Nuclear equations show changes in nuclear reactions using atomic symbols.
• Mass and atomic numbers are conserved in nuclear equations.

Radioactive Decay

• Radioactive decay is a process where an unstable nucleus breaks down by emitting radiation.
• The decay is described by a nuclear equation showing the radioactive nucleus, new nucleus, and radiation emitted (α, β, β+, γ).

Units of Radiation Measurement

• Curie (Ci): the number of disintegrations per second for 1 gram of radium.
• Becquerel (Bq): the SI unit of activity (1 disintegration per second).
• Rad (radiation absorbed dose): measures the amount of radiation absorbed by a gram of material.
• Rem (radiation equivalent in humans): measures the biological effects of different kinds of radiation on humans.
• Conversion factors exist to account for the different penetration power and biological effects of different types of radiation.

Radiation Exposure

• The average person in the US is annually exposed to 3.6 mSv of radiation.
• Natural sources (buildings, food, water).
• Medical sources (X-rays, mammograms)
• High levels of radiation exposure can cause radiation sickness.
• Lethal doses exist for different life forms.

Medical Applications Using Radioactivity

• Different radioisotopes with short half-lives are utilized to diagnose and treat diseases.
• Body cells do not discriminate between radioactive and normal atoms.
• The emitted radiation from the radioisotope is used to produce images of the organ.
• Different organs and diseases can be identified by different isotopes.
• Examples of radioisotopes include I-131 for thyroid, Ga-68 for pancreas, and Tc-99m for brain/bone scans.

Radiological Dating

• Radiological dating is a technique used by geologists, archaeologists, and historians to determine the age of ancient objects.
• It is determined by measuring the amount of Carbon-14, a radioactive isotope, present.
• The uptake of carbon-14 in CO₂ stops when the plant dies.
• As carbon-14 decays, the amount of radioactive carbon decreases.
• Half-life of carbon-14 is used to calculate the time since the plant died

Nuclear Fission and Fusion

• Fission: A large nucleus is bombarded with particles (e.g., neutron), causing it to split into smaller nuclei and releasing a large amount of energy.
• Fusion: Small nuclei combine to form a larger nucleus, releasing a large amount of energy at extremely high temperatures (e.g., Sun and stars).
• Nuclear power plants use fission to generate electricity.

Nuclear Power Plants

• Nuclear fission in power plants utilizes controlled processes of U-235 to produce energy.
• Critical mass is kept below the critical value to control the process.