There are about five atoms left after 48,240 years.
Radioactivity is the spontaneous disintegration of an atom to yield daughter nuclei.
Using the formula;
0.693/t1/2 = 2.303/t log No/N
Where;
t1/2 = half life of the atom
No = initial number of atoms present
N = number of atoms at time t
Substituting values;
0.693/24,120 = 2.303/48,240 log 20/N
0.693/24,120 × 48,240/2.303 = log 20/N
33430/55548 = log 20/N
0.60 = log 20/N
Antilog (0.60) = 20/N
N = 20/Antilog (0.60)
N = 5
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