Introduction to Radiation: Radiation Units

1. Introduction to Radiation: Radiation Units ©Health Physics Society

2. Introduction to Radiation • Objectives • To provide useful information about radiation for interested individuals • To introduce basic concepts of radiation and radioactivity • To improve understanding of radiation – what it is and how it interacts

3. Radioactivity Units • International Unit • becquerel (Bq) • U.S. Unit • curie (Ci) • 1 Ci = 37 GBq • 1 mCi = 37 MBq • 1 µCi = 37 kBq

4. Radiation Exposure Units • International Unit • coulomb per kilogram (C/kg) • U.S. Unit • roentgen (R) • defined only for measurement in air • applies only to x and gamma rays up to energies of about 3 MeV • 1 R = 2.58 x 10-4 C/kg • 1 mR = 0.258 C/kg • 1 µR = 258 C/kg

5. Radiation Exposure Units • Roentgen • Historically used to measure the amount of energy in a photon beam just prior to entering the skin of a patient • Often still used when discussing the entrance skin exposure for medical x-ray exams

6. Radiation Absorbed Dose Units • International Unit • gray (Gy) • U.S. Unit • rad • 1 rad = 0.01 Gy • 1 mrad = 0.01 mGy • 1 µrad = 0.01 µGy

7. Radiation Absorbed Dose Units • Radiation absorbed dose is the amount of energy deposited per unit of tissue. • It is usually measured in ergs per gram or joules per kilogram.

8. Radiation Effective Dose Units • International Unit • sievert (Sv) • U.S. Unit • rem • 1 rem = 0.01 Sv • 1 mrem = 0.01 mSv • 1 µrem = 0.01 µSv

9. Radiation Effective Dose Units • Effective dose is used to represent “how good” the absorbed dose of radiation might be at producing an effect – so it accounts for the effectiveness or quality of the radiation. • Effective dose also includes a factor representing the sensitivity of the tissue to the radiation – so it also accounts for how the tissue might react.