Radioactivity – problems and solutions

1. Based on the figure below, radioactive activity after decay for 13.86 hours is …

Known :Radioactivity – problems and solutions 1

Half-life (T1/2) = 6.93 hours

Time-lapse (t) = 13.86 hours

Wanted: radioactive activity

Solution :

Radioactivity – problems and solutions 2

A = radioactive activity, λ = the decay constant, Nt = The number of radioactive atoms after decaying during a certain time interval, T1/2 = half-life

The decay constant :

Radioactivity – problems and solutions 3

The number of radioactive atoms after decaying during a certain time interval :

Radioactivity – problems and solutions 4

Radioactive activity :

Radioactivity – problems and solutions 5

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2. Based on the figure below, after the radioactive substance decays for 15 minutes, then the remaining radioactive substance is …

Solution :Radioactivity – problems and solutions 6

Radioactivity – problems and solutions 7

No = The initial amount of the radioactive atoms

Nt = The final amount of the radioactive atoms after decaying during a certain time interval (t)

t = time-lapse

T 1/2 = half-life

Calculate the Half-life :

Known :

No = 8 grams

Nt = 2 grams

t = 6 minutes

Wanted: half-life (T 1/2)

Solution :

Radioactivity – problems and solutions 8

Calculate the remaining radioactive material :

Known :

The initial amount of the radioactive atoms (No) = 8 grams

Time-lapse (t) = 15 minutes

Half-life (T 1/2) = 3 minutes

Wanted: the remaining radioactive material (Nt)

Solution :

Radioactivity – problems and solutions 9

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