Rovnice rozpadu:
N = N0*e^(−λt)
t1=1972
t2=2012
Δt=t2-t1
Δt=2012-1972=40 toků
N0=400 kBq
N=25 kBq
N = N0*e^(−λt)
25 = 400*e^(−λ*40)
ln(25/400)/40 = −λ
λ = ln(2)/T½
-ln(25/400)/40 = ln(2)/T½
(-ln(25/400)/40)/ln(2) = 1/T½
ln(2)/(ln(400/25)/40) = T½
T½=10 roků
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viz
https://www.ontola.com/cs/di/polocas-rozpadu-priklad
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ln(2)/(ln(16)/40) =
ln(2)/(ln(2^4)/40) =
ln(2)/4*(ln(2)/40) =
1/4*(1/40) =10