5.1: Natural Radioactivity

• An unstable nucleus is radioactive, which means that it spontaneously emits small particles of energy called radiation to become more stable.

• Radioisotope: An isotope of an element that emits radiation.

• Atomic Symbols: Written with the mass number in the upper left corner and the atomic number in the lower left corner.

• Mass Number: The sum of the numbers of protons and neutrons in the nucleus.

• Atomic Number: It is equal to the number of protons.

Types of Radiation

• Alpha Particle: It has two protons and two neutrons.

  • It has a mass number of 4, an atomic number of 2, and a charge of 2+.

• Beta Particle: It is a high-energy electron, has a charge of 1–, and it has a mass number of 0.

  • It is formed when a neutron in an unstable nucleus changes into a proton.

• Positron: It has a positive charge with a mass number of 0.

  • It is produced by an unstable nucleus when a proton is transformed into a neutron and a positron.

  • Antimatter: A particle that is the opposite of another particle — an electron.

• Gamma Rays: These are high-energy radiation, released when an unstable nucleus undergoes a rearrangement of its particle to give a more stable, lower-energy nucleus.

5.2: Nuclear Reactions

• Radioactive Decay: A process where a nucleus spontaneously breaks down by emitting radiation.

• Alpha Decay: An unstable nucleus may emit an alpha particle, which consists of two protons and two neutrons.

  • The mass number of the radioactive nucleus decreases by 4, and its atomic number decreases by 2.

  • Americium-241: Mostly found in smoke detectors used in homes and apartments, which undergoes alpha decay.

• Beta Decay: The formation of beta particles results from the breakdown of a neutron into a proton and an electron.

  • The mass number of the radioactive nucleus and the mass number of the new nucleus is the same.

  • Radioactive Isotope Yttrium–90: A beta emitter, is used in cancer treatment and as a colloidal injection into large joints to relieve the pain of arthritis.

• Positron Emission

  • A proton in an unstable nucleus is converted to a neutron and a positron.

  • The neutron remains in the nucleus, but the positron is emitted from the nucleus.

  • The mass number of the radioactive nucleus and the mass number of the new nucleus is the same.

  • The atomic number decreases by one, indicating a change in one element into one another.

• Gamma Emission: Pure gamma emitters are rare, although gamma radiation accompanies most alpha and beta radiation.

• Transmutation: A stable nucleus is bombarded by high-speed particles such as alpha particles, protons, neutrons, and small nuclei.

5.3: Radiation Measurements

• When a radiology laboratory obtains a radioisotope, the activity of the sample is measured in terms of the number of nuclear disintegrations per second.

• Curie (Ci): The original unit of activity.

  • It was defined as the number of disintegrations that occurs in 1 s for 1 g of radium, which is equal to 3.7 ✕ 10^10 disintegrations/s.

  • It was named after Marie Curie and her husband, Pierre, who discovered the radioactive elements; radium and polonium.

• Becquerel (Bq): The SI unit of radiation activity, is 1 disintegration/s.

• Radiation Absorbed Dose (Rad): A unit that measures the amount of radiation absorbed by a gram of a material such as body tissue.

• Gray (Gy): The SI unit for absorbed dose.

  • The joules of energy absorbed by 1 kg of body tissue/

  • It is equal to 100 rad.

• Radiation Equivalent in Humans (Rem): A unit that measures the biological effects of different kinds of radiation.

  • To determine the equivalent dose or rem dose, the absorbed dose (rad) is multiples by a factor that adjusts for biological damage caused by a particular form of radiation.

• Sievert (Sv): The SI unit for the equivalent dose or biological damage.

  • One sievert is equal to 100 rem.

• Lethal dose for one-half of the population: The amount of radiation to the whole body; the LD50.

5.4: Half-Life of a Radioisotope

• Half-Life: The amount of time it takes for one-half of a sample to decay.

• Decay Curve: A diagram of the decay of a radioactive isotope.

• Phosphorous: A radioisotope used in the treatment of leukemia has a half-life of 14.3 days.

• Radiological dating: A technique used by geologists, archaeologists, and historians to determine the age of ancient objects.

• Carbon Dating (Carbon-14): The method for determining the age of an object containing organic material is by using the properties of radiocarbon, a radioactive isotope of carbon.

5.5: Medical Applications Using Radioactivity

• Scanner: An apparatus used to produce an image of the organ.

  • The gamma rays emitted from the radioisotope in the organ can be used to expose a photographic plate, producing a scan of the organ.

• Radioactive iodine uptake: The standard method of determining thyroid function.

• Positron emission tomography (PET)

  • An imaging method where Positron emitters with short half-lives such as carbon-11, oxygen-15, nitrogen-13, and fluorine-18 are used.

  • Positron-Emitting Isotopes: These are used to study brain function, metabolism, and blood flow.

• Computed Tomography (CT) Scan

  • Another imaging method is used to scan organs such as the brain, lungs, and heart.

  • A computer monitors the absorption of 30 000 X-ray beams directed at successive layers of the target organ.

  • This technique is successful in the identification of hemorrhages, tumors, and atrophy.

• Magnetic resonance imaging (MRI)

  • A powerful imaging technique that does not involve X-ray radiation.

  • It is based on the absorption of energy when the protons in hydrogen atoms are excited by a strong magnetic field.

• Brachytherapy

  • Also known as seed implantation.

  • It is an internal form of radiation therapy.

  • With internal radiation, a high dose of radiation is delivered to a cancerous area, while normal tissue sustains minimal damage.

Medical Applications of Radioisotopes

5.6: Nuclear Fission and Fusion

• Atomic Energy: The energy generated by splitting the atom.

• During the 1930s, scientists bombarding uranium-235 with neutrons discovered that the U-235 nucleus splits into two smaller nuclei and produces a great amount of energy; which led to the discovery of — nuclear fission.

• Chain Reaction: A fission reaction that will continue once it has been initiated by a high-energy neutron bombarding a heavy nucleus such as uranium-235.

• In fission, the bombardment of a large nucleus breaks it apart into smaller nuclei, releasing one or more types of radiation and a great amount of energy.

• In fusion, small nuclei combine to form larger nuclei while great amounts of energy are released.