Radiation Dosimetry and Quantities
Core concepts
Candidates must distinguish the dosimetric quantities and their units: activity (Bq, Ci), exposure (C/kg, R), absorbed dose (Gy), equivalent dose (Sv), and effective dose (Sv). Know the weighting factors: radiation weighting factor w_R (1 for photons/electrons, 20 for alpha), tissue weighting factors w_T, and how equivalent dose (D × w_R) and effective dose (Σ w_T × H_T) are computed. Understand committed dose (committed effective dose from intakes), dose equivalent at depth (Hp(10), Hp(0.07), Hp(3)), and operational quantities used for personal monitoring. Grasp the difference between external and internal dosimetry and the role of bioassay.
Traps
A frequent trap is mixing absorbed dose (Gy) and equivalent dose (Sv) or applying w_R to the whole body when only one organ is exposed. Another is forgetting that alpha emitters are far more hazardous internally than externally. Watch for questions on Hp(10) (deep dose) versus Hp(0.07) (skin/extremity).
Worked example
A worker receives 2 mGy from alpha internally to the lung (w_R = 20): equivalent dose = 2 mGy × 20 = 40 mSv. If lung w_T = 0.12, contribution to effective dose ≈ 40 × 0.12 = 4.8 mSv. Rule of thumb: multiply absorbed dose by w_R first, then apply w_T.
Practical points
Personal dosimeters report Hp(10) for whole-body and Hp(0.07) for extremities. Committed dose integrates intake over 50 years for adults.