Radiation Concepts and Sources

Radiation Concepts

• Radiation is the transfer of energy.
• Two types of radiation exist: ionizing and non-ionizing.
• Ionizing radiation can remove an orbital electron from an atom.
• Ionizing radiation creates ion pairs, with an electron as a negative ion, and the remaining atom as a positive ion.
• Categories of ionizing radiation include particulate (alpha and beta) and electromagnetic (ultraviolet, x-ray, gamma).

Sources of Ionizing Radiation

• Natural environmental radiation sources include cosmic (sun and stars), terrestrial (uranium and thorium deposits), and internally deposited radionuclides (potassium-40).
• Radon is the largest natural environmental source of ionizing radiation, being a radioactive gas that originates from uranium decay.
• Natural environmental radiation exposure is approximately 3 mSv.
• Man-made radiation sources include diagnostic X-rays (the largest source), nuclear power generation, research applications, industrial sources, and consumer items.
• Man-made radiation exposure is approximately 3.2 mSv.

Radiation Quantities and Units

Alpha Particle

• Originates from radioactive nuclei of heavy elements.
• Contains two protons and two neutrons (equal to a helium nucleus).
• Atomic mass unit (amu) = 4
• Carries 2 units of positive electric charge.
• Has 4 to 7 MeV of kinetic energy.
• Travels approximately 5 cm in air, ≤0.1 mm in soft tissue.
• Harmless in superficial skin but harmful if internally deposited (e.g. radon in lungs).

Beta Particle

• Originates from radioactive nuclei.
• Atomic mass number = 0
• Carries one unit of positive or negative charge (negatron or positron).
• Negatively charged (negatron).
• Positively charged (positron).
• Also called antimatter.
• Can traverse 10 to 100 cm of air and 1 to 2 cm of soft tissue.

Table 2-5: General Classification of Ionizing Radiation

• Exposure is used to describe the quantity of ionization produced when x-rays or gamma rays interact in air. It's measured by collecting the electric charge.

• The Roentgen (R) is the unit of radiation exposure. It's defined only for air and applies to x-rays and gamma rays up to energies of about 3 MeV.

• The modern definition of the roentgen is 1 Roentgen = 2.58 x 10−4 C of charge per 1 kg of air.

• Exposure rates are often expressed as roentgens per unit time (e.g., R/s, mR/h).

• Exposure is not equal to a radiation dose but can be converted.

• Air kerma (Gya) is the SI unit for radiation exposure or intensity. It's measured in joules per kilogram (J/kg), where 1 J/kg is 1 gray (Gya).

• Absorbed Dose (rad/Gy) refers to the amount of energy deposited per unit mass (e.g., 1 rad = 100 erg/g). The SI unit of absorbed dose is the gray (Gy).

• Kerma refers to kinetic energy released in matter. It can be in air or tissue and is expressed in joules per kilogram.

• Radiation dose equivalent (rem/Sv) is used to describe the dose received by workers and the public.

• The dose equivalent considers the biological damage different types of radiation can inflict.

• Sievert (Sv) is the SI unit of dose equivalent.

• Radioactivity is the activity or intensity of radioactive emission. It's the number of atoms undergoing transformation to new atoms per unit time.

• Curie (Ci) was the standard unit of radioactivity and was equal to the emissions of 1 gram of radium.

• Becquerel (Bq) is the SI unit of radioactivity, equal to 1 transformation per second.