Page 208 - Pharmaceutics IV (02-06-01305)

Radioactive decay : is the process by which an atomic nucleus of an
Unstable atom loses energy by emitting ionizing particles.
The rate of decay ,ʎ of a radionuclide ; number of
disintegrations/unit time .
t, is the average life time of an atom before it decays ,
N of radioactive atoms available in a sample at any point in time
N (t) is a function of the number of radioactive atoms present in the
same amount of sample at the initial time point ,t = 0 , by first order
rate of degradation of radionuclide ( since the rate of degradation
depends on the number of available radioactive nuclei) by equation :

N(t) N ( 0)e-kt

First order equation ,where a measure of the rate of a phenomenon

{N(t)/N(0)} is an exponential function of the rate of phenomenon ʎ , time

the elapsed time. Since ,

ʎ = 1/t

N(t) = N(0)e1/t

N (t ½ ) = N (0)/2

t1/2 = =t Ln 2 = Ln2 / ʎ = 0,639/ʎ

or the rate of decay ʎ ,can be calculated from t1/2 as :
K = Ln2 /t1/2 = 0,639/ t1/2

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