**e**(Euler's number):

A(t) = A(0) * 2 ^ (-t/halflife)

Activity at time "t" =

Activity at time zero

TIMES

2 raised to the [ (-t) / halflife]

This is much more simple than having to use the constant

**e**

e.g.

What is the activity after 6 hours for 10 mCi of Tc99m ?

A(t) = the unknown

halflife = 360 minutes for Tc99m

t = 360 minutes

A(0) = 10 mCi

2 raised to the (-360/360) = 2 raised to the -1 = 1/2

therefore....

A(t) = 10 * 1/2 = 5 mCi

A = Ao * 2 ^ (-t/halflife)

much more simple!

This is how I was taught in 1993 and it is much more simple than using

**e**- Tom Heston