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1 - Inverse Square Law

 I2 = I1 [ d1 d2 ] 2 I2, I1 = Intensity at d2, d1 d2, d1= Distance to source

2 - Activity

 a) Ai = 0.693 T1/2 Ni Ai = Initial Activity in Becq. (ps) Ni= Initial Number of Atoms T1/2 = Half - Life in seconds A = Activity (dps) in Becq. t = time elasped in seconds e = natural log b) A = Ai(0.5) t T1/2 c) A = Aie -0.693t T1/2

3 - Exposure & Dose

a)  Rad = 0.869 (f-factor) (Roentgens)
b)  rem = rad x Quality Factor
c)  Life Accumulation = 5 x (N-18) in rem      N = Age in years

4 - Exposure Rate

 D = Γ A d 2 D = Exposure rate (R/hr) Γ = Specific gamma ray constant in units of R · cm2/mCi · hour d = distance from source in cm A = Activity in mCi of the isotope

5 - Shielding

 a) I = (1/2) A I0 I = Intensity on other side of shield I0 = Intensity without shield (R/hr) A = Number of Half-Value-Layers (HVL) HVL = Shield thickness needed to reduce exposure by half. B = Number of Tenth-Value-Layers (TVL) TVL = Shield thickness needed to reduce exposure by 1/10th. x = Shield thickness b) I = ( 1 10 ) B I0 C) I = I0 2 ( x HVL )
 d) x = 3.32 Log [ I0 I ] [ HVL ] or x = Log ( I0 I ) HVL Log 2

6 - Effective Half - Life

 1 T 1/2 eff = 1 T 1/2 rad + 1 T 1/2 bio T1/2eff = Effective Half - Life T1/2rad = Half-Life of internal radioisotope or source T1/2bio = Time for the body to eliminate half of the source. or T 1/2 eff = T 1/2 rad   x   T 1/2 bio T 1/2 rad   +   T 1/2 bio