Radiation Exposure Pathways Quiz

Exposure Pathway and Absorbed Dose

• Exposure pathway is the route a radioactive material takes to enter the body.
• Main routes are inhalation, ingestion, absorption (through skin), and entry through cuts or wounds.

Internal and External Exposure

• External exposure comes from sources outside the body (outer space, sun, suspended particles, radiation generators, buildings, ground).
• Internal exposure comes from sources inside the body (inhaled material, ingested food/drink, radiopharmaceuticals).
• The body is equally exposed to radiation in both cases.

Various Forms of Exposure

• External exposure (whole-body): Exposure to radiation from all over the body.
• External exposure (local): Exposure to radiation from a specific area of the body (e.g., x-ray examination or local contamination).
• Internal exposure (whole-body): Exposure to radiation affecting the entire body.
• Internal exposure (local): Exposure localized in a part of the body (e.g., thyroid exposure through radioactive iodine).

Protection of Individuals Against Radiation

• Protecting people from radiation requires three tasks:
  • Constructing instruments to measure radiation intensity.
  • Establishing units to measure radiation.
  • Developing safe radiation exposure limits based on biological interactions.

Radiation Effect Measurement

• Radiation effect is measured by exposure or dose.
• Exposure is defined as the charge released per unit mass of air.
• Dose is defined as the energy absorbed per unit mass of material.

The Roentgen (R)

• Roentgen (R) was the first radiation unit.
• 1 R = exposure to x-rays or gamma rays of specific intensity, producing electrons in 1 cm³ of dry air (standard temperature and pressure).
• The electrons create ionization pairs along their tracks.
• 1 R = 2.58 x 10⁻⁴ C/kg (coulombs per kilogram)

Limitations of the Roentgen

• Only defined for electromagnetic radiation (x-rays, gamma rays).
• Only defined for air.

Absorbed Dose (rad/Gray (Gy))

• The rad (radiation absorbed dose) was introduced to overcome Roentgen's limitations.
• 1 rad = 100 erg/g (ergs per gram).
• The SI unit for absorbed dose is the gray (Gy).
• 1 Gy = 1 J/kg (joules per kilogram).
• 1 Gy = 100 rad.

Measuring Absorbed Dose

• Measuring absorbed dose (rad/Gy) is often challenging.
• Energy deposited in air can be measured to bypass this.
• Ionization chambers are used to measure exposure, which can be converted to absorbed dose.

Relationship Between Absorbed Dose (D) and Exposure (X)

• D = 0.88X.

Importance of Absorbed Dose Units

• Absorbed dose units are crucial for assessing radiation effects on inanimate objects, like irradiated transistors or nuclear reactor materials.
• For human protection, biological effects of radiation exposure are more vital than the amount of energy deposited.

Relative Biological Effectiveness (RBE)

• RBE is a measure of the relative effectiveness of different types of radiation in producing biological damage.
• RBE is determined relative to the biological effect and energy of radiation in certain circumstances.
• For electromagnetic radiation, RBE = 1.

Factors Affecting RBE

• Energy of radiation.
• Type of cell.
• Biological effect under study.
• Total dose.
• Dose rate.

Linear Energy Transfer (LET)

• LET refers to the energy transferred by radiation to matter per unit length.
• Biological damage increases with LET.
• Heavier charged particles (alphas, heavy ions, fission fragments) cause more biological damage than photons, electrons, and positrons (at same dose).

Quality Factor (QF)

• QF values in ICRU Recommendations replace RBE values.
• QF considers LET in modifying the effectiveness of a given absorbed dose.
• QF is assigned based on multiple factors.

Dose Equivalent (H)

• Dose equivalent (H) is a measure of radiation dose considering its biological effects on humans.
• H is calculated by multiplying the absorbed dose by a qualifying factor (Q).
• 1 rem = Q × 1 rad, and 1 Sv = Q × 1 Gy are units of dose equivalent.

Conversion Between Units

• 1 Sv = 100 rem.

Important Note on Dose Equivalent

• Only dose equivalent (Sv or rem) sums up for equalizing biological effects from different types/energies of radiation.

Exposure to Specific Radioisotopes (e.g., strontium, radium, iodine)

• Certain radioactive isotopes can cause localized damage by replacing calcium in bones.
• Some isotopes can deposit in bone marrow (blood-forming tissues), which might lead to leukemia.
• Radioisotopes have long half-lives and cause significant health hazards.
• Exposure to these isotopes can lead to severe localized or systemic effects due to the localized damage, particularly affecting developing tissues.

Exposure to Iodine Radioisotopes and Thyroid Damage

• Iodine isotopes can damage the thyroid, which is essential for hormone regulation (T4 and T3).
• Thyroid damage can affect growth and metabolic rates in the body.
• Because children's cells divide more frequently, radiation exposure can gravely harm children.

OSHA Regulations on Radiation Exposure

• OSHA sets limits on radiation exposure for workers
• Workers should not exceed permissible exposure limits (PEL) in any calendar quarter.
• The permissible whole-body dose in a quarter has an upper limit.
• Accumulated dose per year (including occupational and other doses) should not exceed 5 x(age - 18).

Warning Signs for Radiation Areas

• Specific warning signs are mandatory in areas with elevated radiation.
• Signs include the trefoil symbol plus the word CAUTION plus the type and level of radiation hazard (Radiation Area, High Radiation Area, Airborne Radioactivity Areas).

Permissible Exposure Limits

• OSHA outlines permissible exposure limits for various types of radiation.
• These are given in Table 16.5 by rem/year.