Radioactive decay is a natural, spontaneous, and random process by which an unstable nucleus releases radiation to achieve greater stability. Explore alpha, beta and gamma emissions, decay series, half-life and radioactive dating.
Compare how alpha, beta and gamma emissions change a nucleus, then read the exponential decay curve using half-life steps.
Parent nucleus emits a helium nucleus.
\(^{A}_{Z}\mathrm{X} \rightarrow\ ^{A-4}_{Z-2}\mathrm{Y} +\ ^{4}_{2}\mathrm{He}\)
A neutron changes into a proton and an electron.
\(^{A}_{Z}\mathrm{X} \rightarrow\ ^{A}_{Z+1}\mathrm{Y} +\ ^{0}_{-1}\mathrm{e}\)
An excited nucleus releases excess energy.
\(^{A}_{Z}\mathrm{X} \rightarrow\ ^{A}_{Z}\mathrm{X} + \gamma\)
Radioactive decay is a process in which an unstable nucleus becomes more stable by emitting radioactive radiation. It is spontaneous and random.
An alpha particle is \(^{4}_{2}\mathrm{He}\). A beta particle is \(^{0}_{-1}\mathrm{e}\). A gamma ray is a high-frequency electromagnetic wave.
Alpha decay general equation
Proton number decreases by 2, nucleon number decreases by 4.
Beta decay general equation
Proton number increases by 1, nucleon number remains unchanged.
Gamma decay general equation
No change in proton number or nucleon number; excess energy is released.
A continuous series of successive decays starts from an unstable parent nucleus and passes through intermediate daughter nuclei until a stable nucleus is reached. The uranium-238 series begins at \(^{238}_{92}\mathrm{U}\) and ends at stable \(^{206}_{82}\mathrm{Pb}\).
Half-life \(T_{\frac{1}{2}}\) is the time taken for half of the radioactive nuclei in a sample to decay. Activity \(A\) is the number of decays per second.
Remaining nuclei and activity after n half-lives
where \(n = \frac{t}{T_{\frac{1}{2}}}\).
Answer in your mind, then press “Check Answer”.
What happens to the nucleon number and proton number of a nucleus after emitting a beta particle?
A radioactive sample has an initial activity of \(800\ \mathrm{s^{-1}}\). If its half-life is 4 hours, what will its activity be after 12 hours?
Why cannot radioactive decay be accelerated by raising the temperature or pressure of the sample?
Radioactive materials decay completely to zero at the end of two half-lives because \(50\% + 50\% = 100\%\).
In each successive half-life, half of the remaining nuclei decay. After 1 half-life, \(50\%\) remains; after 2 half-lives, \(25\%\) remains; after 3 half-lives, \(12.5\%\) remains.
“Spontaneous” means the decay occurs instantaneously or very rapidly.
“Spontaneous” means the decay occurs naturally without requiring external initiation and is unaffected by external environmental factors such as temperature or pressure.
Beta particles come from the electron shells surrounding the nucleus.
A beta particle is an electron that originates from inside the nucleus when an unstable neutron decomposes into a proton and an electron.
Objective: Check your understanding of radioactive decay, half-life and decay equations.
1 Which statement correctly describes the change in a nucleus when it undergoes beta decay?
2 A sample of radioisotope has an initial activity of \(1\,200\ \mathrm{s^{-1}}\) and a half-life of 15 minutes. What is its activity after 45 minutes?
3 Radioactive decay is described as because it occurs naturally without being influenced by external physical factors like temperature and pressure.
4 An alpha particle is identical to the nucleus of a helium atom, consisting of two protons and two .
Drag each term to the correct meaning. If using a phone, tap the answer first, then tap the matching box.
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