Radiochemistry and Radioactivity

Radiochemistry

• Radioactivity is a natural phenomenon that occurs in certain substances, where atoms emit invisible and energetic radiations that can penetrate materials opaque to visible light.
• These radiations can be harmful to live cells, but they have beneficial applications in medicine when used correctly.

Units of Radioactivity

• The amount of radioactivity is measured by the rate of radioactive disintegration per second.
• The Curie (Ci) is a unit of radioactivity, equivalent to 3.7 x 10^10 disintegrations per second.
• 1 Curie is equal to 3.7 x 10^10 Becquerel.

Isotopes

• An isotope is a variant of a chemical element, with the same number of protons (atomic number) but a different number of neutrons.
• Isotopes can be stable or radioactive, and radioisotopes undergo spontaneous decay and emit radiation.
• The stability of an isotope depends on the balance of neutrons and protons.

Radioisotopes

• Radioisotopes are isotopes that undergo spontaneous decay and emit radiation.
• They become less radioactive over time, eventually becoming stable.
• The half-life of a radioisotope is the time it takes for the activity to fall to half of its original value.

Half-Life

• The half-life of a radioactive source is the time it takes for the activity to fall to half of its original value.
• The activity of a radioisotope decreases exponentially with time, halving every half-life.
• The half-life of a radioisotope is different for each substance.

The Atom

• An atom is the smallest unit of matter, consisting of a nucleus and orbiting electrons.
• The nucleus is composed of protons and neutrons, and the number of protons determines the atomic number (Z).
• The atomic number and mass number (A) determine the identity of an element.

Structure of the Atom

• The nucleus is composed of protons and neutrons.
• The atomic number (Z) is the number of protons in the nucleus.
• The mass number (A) is the sum of protons and neutrons in the nucleus.

Types of Radiation

• Alpha radiation is a stream of particles with two protons and two neutrons, having a charge of +2.
• Beta radiation is a stream of electrons, resulting from the transformation of a neutron into a proton and electron.
• Gamma radiation is a form of energy, similar to light waves or X-rays, with high energy and penetration.
• Electron Capture or Ionization radiation is a process where an electron is given enough energy to break away from an atom.

Nuclear Reaction

• Nuclear reactions involve the collision of atomic nuclei or a nucleus and a subatomic particle.
• The resulting nuclides are different from the parent nuclei.

Forms and Properties of Nuclear Radiation

• Alpha radiation has a charge of +2 and a symbol of α or 4He.
• Beta radiation has a charge of -1 and a symbol of β or -10e.
• Gamma radiation has a charge of 0 and a symbol of γ.
• Positron radiation has a charge of +1 and a symbol of +10e.
• Neutron radiation has a charge of 0 and a symbol of n.

Ionization Radiation

• Ionization radiation is the process where an electron is given enough energy to break away from an atom.
• This results in the formation of two charged particles or ions: a positively charged molecule and a negatively charged electron.

Alpha Decay

• Alpha decay occurs when a nucleus with a mass number greater than 200 liberates a helium nucleus (alpha particle).
• The general equation for alpha decay is: A-ZX → A-4Z-2X + α.

Beta Decay

• Beta decay occurs when a neutron is converted into a proton, accompanied by the emission of a beta particle (high-energy electron).
• The equation for beta decay is: A-ZX → A-Z+1X + -10e.

Gamma Emission

• Gamma emission occurs when an excited nucleus returns to its ground state, accompanied by the emission of a high-energy photon.
• The equation for gamma emission is: A-ZX → A-ZX + γ.

Ionizing Radiation

• Ionizing radiation is energy produced from natural or artificial sources, with enough energy to cause chemical changes in living tissue.
• X-ray and gamma ray radiation are at the upper end of the electromagnetic spectrum, with high frequencies and short wavelengths.
• Ionizing radiation deposits a large amount of energy into a small area, disrupting chemical bonds and causing damage.

Radiation Dose

• Radiation dose measures the energy deposited by ionizing radiation in a material.
• The concept of absorbed dose applies to all types of material, but when assessing biological effects, the equivalent dose is used, which takes into account the radiation weighting factor.
• The equivalent dose is measured in units of Rem, which is 1 rad multiplied by the relative biological equivalence (RBE).

Units of Radiation Dose

• Rad is a unit of radiation dose, equivalent to 2.4 x 10^-3 cal of energy absorbed by 1 kg of tissue.
• Rem is a unit of radiation dose, equivalent to 1 rad multiplied by the RBE.

Direct and Indirect Action

• Direct action occurs when the atoms of the target are ionized by the radiation.
• Indirect action occurs when the radiation interacts with other cellular molecules, producing free radicals that damage the target.

Radiation Detectors

• The three methods of detecting ionizing radiation are the photographic method, scintillation counter, and Geiger counter.
• Geiger counters are gas-filled detectors that use an electric potential to collect electrons released by ionizing radiation.

Medical Applications of Isotopes

• The half-life of an isotope must be long enough for it to do its job and short enough to eliminate it from the body.
• In medical applications, no alpha radiation is used due to its damaging effects on tissues.
• The main mechanism for isotopes application is either externally (such as Co-60) or internally (such as I-131).
• The table below shows the main isotopes used in medical applications:

Learn about the natural phenomenon of radioactivity, its effects on living cells, and its beneficial applications in medicine.