Radiation Units :Radiation Units


Radiation Units Exist for: :Radiation Units Exist for: Activity Exposure Absorbed Dose Dose Equivalent


Activity :Activity Indicates the amount of radioactive substance present at any given time in a sample or source


Commonly Used Activity Units: :Commonly Used Activity Units: microcuries (?Ci) or kilobecquerels (kBq) - represents low activity millicuries (mCi) or megabecquerels (mBq) - represents moderate to high activity Curies (Ci) or gigabecquerels (GBq) - represents very high activity


Activity Units :Activity Units


Physical Half-Life (T1/2) :Physical Half-Life (T1/2) One recalls that the activity of a radioactive source that remains at any time is related to its physical half-life. The physical half-life being that time required for 50% of a radioactive sample to decay away.


Exposure & Exposure Rate :Exposure & Exposure Rate Exposure: a measure of the amount of radiation to which one has been exposed Units: Roentgens (R), milliroentgens (mR) or Coulombs/kg (C/kg) Exposure rate: measures exposure received per unit time Units: R/hr or mR/hr


Sample Problem :Sample Problem How much radiation exposure does one receive by working in an workplace area where the exposure rate is 120 mR/hr for 3 hours? Exposure Rate x Time = Exposure 120 mR/hr x 3 hrs = 360 mR


Absorbed Dose :Absorbed Dose Takes into account that the body does not absorb all the radiation to which it is exposed. The fraction (f) of the incident energy which is absorbed depends upon the radiation energy and the absorber.


Units of Absorbed Dose: :Units of Absorbed Dose: Rads or Grays Note: 1 rad = 100 ergs/gm of absorber 1 Gray = 1 Joule/kg of absorber Therefore, 1 Gray = 100 rads Absorbed Dose = (F-factor)(Expsoure) f ˜ 1 for x and ?-rays for the energy range used in medicine so, Absorbed Dose = Exposure


Dose Equivalent :Dose Equivalent Accounts for the fact that certain types of radiation are more biologically damaging than others Units: Rems or Sieverts (Sv) Dose Equivalent = (Q factor)(Absorbed Dose) Note: Q-factor = quality factor


Recommended Quality Factors* :Recommended Quality Factors* X-rays, ?-rays and ß’s 1 Neutrons 5 – 20 a-particles 20 *From the NRCP report 91 (1987)


Sample Problem :Sample Problem Determine the dose equivalent which results from an exposure of 60 mR from 180keV x-rays. Dose Equivalent = (Exposure)(f)(Q) = (60mR)(1)(1) = 60 mrem


Radiation Units Summary :Radiation Units Summary Activity: 1 Curie (Ci) = 3.7 x 1010 dps 1 Becquerel (Bq) = 1 dps Therefore, 1 ?Ci = 37 kBq 1 mCi = 37 MBq


Radiation Units Summary :Radiation Units Summary Exposure: 1 Roentgen (R) = 2.58 x 10-4 C/kg (air) 1 C/kg ? 3876 Roentgen Exposure = Exposure Rate x Time


Radiation Units Summary :Radiation Units Summary Absorbed Dose: 1 Gray = 100 rads 1 rad = 1 centigray (cGy) Dose Equivalent 1 Sievert = 100 rem 1 rem = 1 centisievert (cSv)