Radiation Dose: The amount of radiation absorbed by an object or person.

Radiation Activity: The rate at which a sample of radioactive material decays, measured in disintegrations per second.

Symbol and Units

Radiation Dose

• Gray (Gy): The SI unit of absorbed radiation dose, one joule per kilogram.
• Sievert (Sv): The SI unit of equivalent radiation dose, which considers the biological effect of radiation.
• Rad: An older unit of absorbed dose, where 1 rad = 0.01 Gy.
• Rem: An older unit of equivalent dose, where 1 rem = 0.01 Sv.

Radiation Activity

• Becquerel (Bq): The SI unit of radioactivity, one disintegration per second.
• Curie (Ci): A non-SI unit of radioactivity, equivalent to 3.7 x 10¹⁰ disintegrations per second.
• Rutherford (Rd): A unit of radioactivity equal to 10⁶ disintegrations per second.

Formula

Absorbed Dose (D): \( D = \frac{E}{m} \), where \( E \) is the energy deposited and \( m \) is the mass of the material.

Equivalent Dose (H): \( H = D \times W_R \), where \( W_R \) is the radiation weighting factor.

Activity (A): \( A = \lambda N \), where \( \lambda \) is the decay constant and \( N \) is the number of undecayed nuclei.

Key Points

• Radiation dose measures the amount of radiation energy absorbed, while activity measures the rate of radioactive decay.
• The Gray (Gy) is used for absorbed dose and the Sievert (Sv) is used for equivalent dose, accounting for biological effects.
• Becquerel (Bq) is the SI unit for activity, while the Curie (Ci) is a larger, non-SI unit often used in the field.
• Rutherford (Rd) is another unit of activity used in some contexts.

Applications

• Medical: Radiation therapy, diagnostic imaging, and nuclear medicine.
• Industrial: Non-destructive testing, sterilization, and power generation in nuclear reactors.
• Environmental: Monitoring and controlling environmental radiation levels.

Material Variance

• Different materials absorb and respond to radiation differently, affecting both the dose and biological impact.
• Heavy elements like lead are used for shielding due to their high absorption capacity.

Examples

Example 1: Convert 2 Gy to Sv for gamma radiation (WR = 1):

2 Gy = 2 Sv

Example 2: Convert 5 Ci to Bq:

5 Ci = 5 × 3.7 × 10¹⁰ Bq = 1.85 × 10¹¹ Bq

Example 3: Convert 1 Rd to Bq:

1 Rd = 1 × 10⁶ Bq