The radioactive constant or
decay constant ( l ), is a coefficient of
proportionality which relates the atoms which disappear in a period of
time
t, (-dN) with the initial atoms (No ) for each radioactive nuclide :-dN
= - l N dt
The above expression can also be written: -dN / No dt = l .
l measures the
probability of transformation of an atom in the unit of time.
If from 100 initial atoms 1 disintegrates evey second, the probability
of disintegration is 1/100 = 0,01 = 1% per second.
The unit of l is [T -1 ],
that is any unit of time elevated to minus one.
So, if the l of Ra is 0.00042 years-1
= 1 / 2381 per year, this indicates that the probability of radioactive
disintegration is one atom for every 2381 radioactive atoms in one year
(0.00042 = 0.042%). This may seem very little, but remember that 1 mol
of uranium (238.02 g) contains 6.02·10 -23 atoms.
