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Lecture Notes: Radiation Biology & Protection — Vocabulary

Particulate Alpha/Beta and Ionizing Radiation

  • Alpha radiation: heavy particles; limited travel distance (does not penetrate well).
  • Beta radiation: lighter than alpha; somewhat more penetrating than alpha but still relatively limited.
  • Gamma and X-radiation are electromagnetic ionizing radiation; gamma rays come from nuclei of radioactive materials; X-rays are man-made from X-ray tubes.

Electromagnetic Radiation and Biological Effects

  • X-rays: man-made, produced by X-ray tubes.
  • Gamma rays: originate from nuclei of radioactive materials.
  • Ionizing radiation (biological effects): factors to consider include:
    • The material being irradiated.
    • The rate of radiation exposure (the dose rate): the amount received over a period of time.
    • Biological response varies with dose rate; the same total dose given at different rates can yield different effects.
    • Example consideration mentioned: 2 Gy from alpha radiation may be lethal; 2 Gy from gamma radiation may be survivable, illustrating different radiobiological effectiveness depending on radiation quality.
  • Type of Radiation and Radiosensitivity:
    • Immature (or developing) cells are more radiosensitive.
    • Young age generally associated with higher radiosensitivity; old age with lower radiosensitivity.
    • Differentiated cells may have varying sensitivity.
    • Tissue type matters; reproductive tissues are particularly radiosensitive.
    • Sex differences noted: females are described as more radiosensitive; males are described as less radiosensitive (as stated in the transcript).
    • Knowledge of which tissues are involved (e.g., muscle tissue, reproductive organs) is important for assessing risk.

Somatic vs Genetic Effects (Biological Classification)

-Somatic effects (on the body organs, excluding reproduction):

  • Skin (reddening), burns, changes in blood components (blood count), cataracts in the lens, etc.
    • Genetic effects (on offspring):
  • Effects transmitted to the embryo/fetus, i.e., mutations in germ cells leading to offspring changes.
  • The transcript mentions eggs and sperm as relevant reproductive cells.

Sources of Radiation (Overview)

  • Background natural radiation:
    • Cosmic radiation from space and the sun.
    • Terrestrial radionuclides in the ground.
    • Radionuclides found internally within the body.
    • Radon and thoron gas in the ground that seeps into buildings; exposure is higher in winter.
  • Man-made radiation (medical, industrial, consumer products):
    • Medical imaging and procedures (X-ray imaging, CT, nuclear medicine).
    • Pharmaceutical radiopharmaceuticals.
    • Consumer products that emit radiation.
    • Air travel exposure (high altitude increases cosmic exposure).
    • Nuclear power plants and associated activities.
    • Nuclear medicine procedures provide exposure from radiopharmaceuticals.
    • The transcript lists multiple medical-related sources, including CT imaging and nuclear medicine, with some percentages or notes that are unclear in the text.

Quantities & Units Relevant to Radiation Protection

  • Quantities and units are discussed in traditional units and SI units.

Traditional vs SI Units

  • Exposure (X): measured in Roentgen (R) or Coulombs per kilogram (C/kg) in SI.
  • 1 R = 2.58 × 10^(-4) C/kg in air.
  • Absorbed dose (D): energy deposited per unit mass, measured in rad (traditional) or gray (Gy, SI).
    • 1 Gy = 100 rad.
    • 1 rad = 0.01 Gy.
  • Radiation energy deposition and interpretation:
    • X-ray exposure relates to energy deposited in tissue; higher energy and penetration influence dose distribution.
  • Dose energy terminology:
    • In the traditional system, dose in energy terms used to be described as rad; in SI, Gy.
    • 1 Gy = 1 J/kg.

Dose Quantities and Their Roles

  • Air Kerma (K): kinetic energy released in matter; historically used to describe the output of an x-ray tube.
    • Measured in Gy (or rad in older terms).
    • Related concept: exposure in air (R or C/kg).
  • Integral Dose: total energy deposited into matter; conceptually the total dose delivered across the irradiated volume; units relate to energy (J).
  • Equivalent Dose (EqD): dose adjusted for radiation type using a radiation weighting factor (w_R) to reflect biological effectiveness.
    • H = D imes w_R
    • Units: sievert (Sv) (since D is Gy, multiplying by w_R yields Sv).
    • For X-ray and gamma, wR ≈ 1; for alpha particles, wR ≈ 20 (higher biological effectiveness).
  • Effective Dose (EfD or E): sum of tissue-weighted doses, accounting for varying radiosensitivities of different tissues.
    • E = \,\sumT wT D_T
    • Units: Sv, where w_T are tissue weighting factors for each tissue T.
    • The tissue weighting factors reflect relative radiosensitivity and the contribution of each tissue to overall risk.

Activity, Radioactivity, and Common Units

  • Activity (A): quantity of radioactive material present.
    • Traditional unit: Curie (Ci).
    • SI unit: Becquerel (Bq).
    • 1 Ci = 3.7 × 10^10 Bq; 1 Bq = 1 decay per second.
  • Practical note: Activity is not typically used in diagnostic imaging dose calculations; it is more relevant for assessing radiopharmaceuticals and radioactive sources.

Relationships and Quick Conversions

  • Exposure vs Air Kerma vs Absorbed Dose:
    • Exposure (R) relates to ionization in air and is connected to C/kg via the factor 1 R ≈ 2.58 × 10^(-4) C/kg in air.
    • Air Kerma (Gy) approximates the energy released in air per unit mass and is a precursor to absorbed dose in tissues.
  • Dose units relationships:
    • 1\ ext{Gy} = 100\ ext{rad}
    • 1\ \text{Sv} = 100\ \text{rem}
    • 1\ \text{Ci} = 3.7 \times 10^{10}\ \text{Bq}
  • The difference between the traditional and SI units is largely historical; modern practice uses Gy for dose and Sv for effective dose.

Practical Implications and Concepts Mentioned in the Transcript

  • Dose rate matters: higher dose rates can cause different biological effects than the same total dose delivered slowly.
  • Radiosensitivity varies with cell type, age, and tissue: immature or stem cells are more sensitive; reproductive tissues are especially sensitive; females are described as more radiosensitive in the transcript; young/early developmental stages are particularly vulnerable.
  • Distinction between somatic and genetic effects guides risk assessment and informed consent in medical procedures.
  • The relative lethality of different radiation types is not only a function of dose but also of radiation quality (LET) and dose distribution across tissues.

Quick Reference Formulas (LaTeX)

  • Exposure in air and ionization:
    • X ext{ (Exposure)} = \text{R} ext{ or } \text{C/kg}
    • 1\ \text{R} = 2.58 \times 10^{-4}\ \text{C/kg in air}
  • Absorbed dose:
    • D = \frac{E}{m}
    • 1\ \text{Gy} = 100\ \text{rad}
    • 1\ \text{rad} = 0.01\ \text{Gy}
    • 1\ \text{Gy} = 1\ \text{J/kg}
  • Equivalent dose:
    • H = D \times w_R
  • Effective dose:
    • E = \sumT wT D_T
  • Radiation weighting factors (example):
    • wR = 1\ (X-ray,\ gamma,\beta)\quad wR = 20\ (\alpha)
  • Activity and radioactivity:
    • A = \text{activity}
    • 1\ \text{Ci} = 3.7 \times 10^{10}\ \text{Bq}
    • 1\ \text{Bq} = 1\ \text{s}^{-1}
  • Common units conversion:
    • 1\ \text{Sv} = 100\ \text{rem}
    • 1\ \text{Gy} = 100\ \text{rad}

Notes and cautions:

  • The transcript contains several typographical errors and ambiguities (e.g., specific percentages for natural sources, exact wording about age-related radiosensitivity). Where numbers are unclear, use the intended concepts (background natural sources, man-made medical sources, dose quantities, and their relationships) and refer to standard radiological protection references for precise values.
  • If your exam requires exact numeric percentages for specific sources (e.g., contributions to natural background radiation), confirm with your instructor or a textbook since the transcript’s percentages are not consistently presented.