Nuclear Chemistry: Radioactivity and Isotopes

Nuclear Chemistry

• Radiation technologists work in hospitals or imaging centers using nuclear medicine to diagnose and treat various medical conditions.

5.1 Natural Radioactivity

• Unstable nuclei spontaneously emit small energy particles (radiation) to become more stable.
• The learning goal is to describe alpha, beta, positron, and gamma radiation.

Radioisotopes

• A radioisotope is an unstable nucleus that emits radiation.
• It can be one or more isotopes of an element.
• Mass numbers are included in its name.
• Carbon-14 is a radioactive isotope used in archeological dating. Its mass number is 14 and its atomic number is 6.

Types of Radiation Emitted

• Radioisotopes emit various types of radiation.
  • Alpha (α) particles are identical to helium nuclei.
  • Beta (β) particles are high-energy electrons.
  • Positrons (β⁺) are antimatter particles that are the same mass as electrons but have a positive charge.
  • Gamma (γ) rays are pure energy.

Alpha Particles

• Alpha particles are identical to helium nuclei.
• They have 2 protons and 2 neutrons.
• Mass number is 4.
• Charge is 2+.
• Low energy compared to other forms of radiation.
• Travel a short distance (2-4 cm) from the source.

Beta Particles

• Beta particles are high-energy electrons.
• Mass number is 0.
• Charge is 1-.
• Formed in unstable nuclei when a neutron changes into a proton and an electron.

Positrons

• Positrons have a mass number of 0.
• Have a charge of 1+.
• Created when a proton changes into a neutron and a positron in an unstable nucleus.

Gamma Rays

• Gamma rays are high-energy radiation.
• Have a mass number of 0 and a charge of 0.
• These are emitted from unstable nuclei to become more stable and have lower energy.

Some Forms of Radiation

• Table details different types of radiation, including their symbols, mass numbers, and charges.

Biological Effects of Radiation

• Ionizing radiation damages molecules along its path.
• Rapidly dividing cells (bone marrow, skin, reproductive organs, and cancer cells) are most sensitive to radiation.
• Cancer cells are highly sensitive to radiation, and high doses are used to destroy them.
• Normal tissue around cancer cells divides more slowly and is less damaged by radiation.
• Radiation can cause malignant tumors, leukemia, anemia, and genetic mutations.

Radiation Protection

• Protection from radiation depends on the type of radiation.
• Alpha particles are stopped by paper and clothing.
• Beta particles are stopped by lab coats or gloves.
• Gamma rays require lead shields or thick concrete walls.
• Limiting time near a radioactive source and increasing distance from the source reduce exposure.

Radiation Protection (additional)

• Different types of radiation penetrate the body to varying depths.
• Wear protective clothing, gloves, and shields when working with radioisotopes.

5.3 Radiation Measurement

• A radiation counter is used to measure radiation levels, like at nuclear power plants.
• The learning goal is to describe how to detect and measure radiation.

Geiger Counter

• A Geiger counter is a common instrument for detecting beta and gamma radiation.
• It uses ions from radiation to create an electric current.

Units for Measuring Radiation

• Units for measuring radiation activity include:
  • Curie (Ci): the number of disintegrations in 1 second for 1 gram of radium (3.7 x 10¹⁰ disintegrations/s).
  • Becquerel (Bq): the SI unit of radiation activity (1 disintegration/s).
  • Rad (radiation absorbed dose): measures the amount of absorbed radiation by a gram of material.
  • Rem (radiation equivalent in humans): measures the biological effects of various types of radiation.

Measuring Radiation Damage

• Rem measures the biological damage from radiation.
• Alpha particles, which don't penetrate skin, can cause significant damage if they enter the body.
• Higher energy radiation, including beta particles, high-energy protons, and neutrons, cause more damage.
• Gamma rays are highly damaging because they travel a long distance through tissue.

Dosimeters Measure Radiation Exposure

• People in radiation labs wear dosimeters to measure radiation exposure.
• They detect exposure to X-rays, gamma rays, and beta particles.

Radiation Exposure

• The average person in the US is exposed to 3.6 mSv of radiation annually.
• Exposure occurs from naturally occurring radioisotopes in buildings, food, water, and air.
• Medical sources include X-rays and mammograms.

Average Annual Radiation Exposure

• A table presents average annual radiation exposure from various sources.

Radiation Sickness

• Exposure to less than 0.25 Sv of radiation is usually undetectable.
• Whole-body exposure to 1 Sv can cause temporary white blood cell decrease.
• Exposure over 1 Sv can induce radiation sickness (nausea, vomiting, fatigue, reduced white blood cells).
• An exposure of 5 Sv is likely to cause death in 50% of the people exposed.

Lethal Dose of Radiation

• The table 5.6 displays lethal doses for different life forms depending on the type of radiation and duration of exposure.

Half-Life of a Radioisotope

• The half-life is the time it takes for a radioisotope’s radiation level to reduce to half of its original value.

Half-Lives of Radioisotopes

• A table listing half-lives of various radioisotopes (natural and medical) with their associated radiation type.

Medical Applications Using Radioactivity

• Different radioisotopes are used to diagnose and treat a variety of diseases.
• Detailed information on specific radioisotopes and their medical applications in a table.

5.2 Nuclear Reactions

• Equations depict changes in nuclear reactions.
• Atomic symbols are used to represent mass and atomic numbers in nuclear equations.

Radioactive Decay and Nuclear Equations

• Unstable nuclei spontaneously break down (decay) by emitting radiation.
• Equations show this breakdown into a new nucleus plus radiation.
• To balance a nuclear equation, the mass numbers and atomic numbers must equal on both sides of the equation.

Alpha Decay

• When alpha particles are emitted, the new nucleus has its mass number decreased by 4 and atomic number by 2.

Beta Decay

• A beta particle is essentially an electron emitted.
• During beta decay, a neutron converts into a proton and a beta particle, increasing the atomic number by one.

Positron Emission

• In positron emission, a proton in an atom changes into a neutron and a positron, decreasing the atomic number by one.

Gamma Emission

• Gamma emission involves emitted energy from an unstable nucleus; the mass number and atomic number of the new nucleus remain the same.