Core Concepts
In this article you will be able to understand what is radioactive decay and its different processes. After reading this article you will differentiate alpha, beta, gamma and other forms of radioactive decay.
Related Topics
Radioactive Decay
An unstable atomic nucleus loses energy by radiation during radioactive decay. Radioactive substances are those that have unstable nuclei. The three most prevalent kinds of decay, alpha, beta, and gamma, all include the emission of particles. You can understand radioactive decay in terms of the four fundamental forces of physics. In particular, the weak nuclear force controls the beta decay process, whereas the alpha and gamma are under the control of the strong nuclear force and electromagnetism, respectively.
Alpha Decay
The atomic nucleus emits an alpha particle, resulting in its transformation into a separate atomic nucleus with a decreased mass number by four and a reduced atomic number by two. This process is known as alpha decay. An alpha particle is the same as the nucleus of a helium-4 atom, consisting of two protons and two neutrons. It weighs 4 Da and has a +2 charge. For example example, the alpha decay of uranium-238 which produces thorium-234.
On Earth, 99% of the helium created comes from the alpha decay of subsurface reserves of minerals containing uranium or thorium. During the extraction of natural gas, the process transports helium to the surface as a byproduct.
Beta Decay
Beta- and beta+ are the names for the two forms of beta decay. After beta- decay, a neutron transforms into a proton, increasing the atomic number by 1 while keeping the mass number unchanged. In contrast, during beta+ decay, also called positron emission, a proton transforms into a neutron, decreasing the atomic number by 1 while keeping the mass number unchanged.
Beta- Decay
In beta decay, a neutron emits an electron (e–) and an antimatter particle called a antineutrino (ve), which then turns the neutron into a proton. During beta decay, the nucleus produces both the electron and antineutrino, rather than these particles being present in the nucleus beforehand. Ultimately, beta decay gives unstable atoms a protons-to-neutrons ratio that is more stable. An atom’s nuclear binding energy determines whether it will decay by beta decay or another type of decay.
Beta+ Decay or Positron Emission
Positron emission, or beta plus decay, occurs when a proton transforms into a neutron, producing a positron (e+) and an electron neutrino (ve). The electron released during the disintegration of a nucleus is another form of beta particle, and the positron (e+) is one of these particles.
In unstable positron emission tomography (PET) scans for medical imaging, fluorine-18 is employed. It degrades as follows by positron emission: 18F (nine neutrons and nine protons) + 18O (eight neutrons and ten protons) + positron + neutrino
Gamma Decay
In gamma decay, unstable atomic nuclei release extra energy in the form of gamma rays. Gamma ray emission follows two distinct steps: internal conversion and internal pair formation. In internal conversion, a nucleus transfers excess energy directly to one of its orbiting electrons, causing the atom to eject the electron. In internal pair formation, excess energy is immediately transformed into an electron and a positron that are released jointly within a nucleus’ electromagnetic field.
After gamma decay there are no changes on the atomic number or the mass of the nuclide.
Electron Capture
The process of electron capture comprises the absorption of an inner atomic electron by the proton-rich nucleus of an electrically neutral atom. In doing so, this conversion changes a nuclear proton into a neutron, and simultaneously releases an electron neutrino.
When there is not enough energy difference between an isotope and its daughter isotope for positron emission, electron capture is the predominant mechanism of decay. For radioactive isotopes with enough energy to undergo positron emission decay, electron capture is always an additional decay mode. Some occasionally classify electron capture as a form of beta decay since the fundamental nuclear mechanism is mediated by the weak nuclear force. While this phrase often pertains to the interaction between an electron antineutrino and a proton, people sometimes also label electron capture as inverse beta decay.
After electron capture, the atomic number decreases by 1 while keeping the mass number unchanged
Radioactive Decay Practice Problems
Problem 1
A radioactive substance undergoes alpha decay, emitting an alpha particle (helium nucleus). If the substance has an atomic number of 88 and a mass of 226, what is the resulting nuclide after alpha decay?
Problem 2
A radioactive isotope decays by beta minus emission, transforming a neutron into a proton. If the isotope has 40 protons and 50 neutrons, what is the atomic and mass number of the resulting nuclide?
Problem 3
A nucleus undergoes positron emission, changing a proton into a neutron. If the nucleus has 29 protons and 35 neutrons, what are the atomic number and mass of the resulting nuclide?
Problem 4
A nucleus experiences electron capture, where an inner-shell electron is captured by a proton. If the nucleus has 60 protons and 90 neutrons, what are the atomic number and mass of the resulting nuclide?
Problem 5
Following alpha decay and beta decay, a nucleus is left in an excited state. It transitions to a lower energy level by emitting a gamma ray photon. If the nucleus has an atomic number of 82 and a mass of 214, what are the atomic number and mass of the resulting nuclide after gamma decay?
Radioactive Decay Practice Problems Solutions
Answer 1
The alpha particle consists of 2 protons and 2 neutrons. The resulting nuclide has an atomic number of 86 and a mass of 222.
Answer 2
Beta decay converts a neutron into a proton, increasing the atomic number by 1 while keeping the mass number unchanged. The resulting nuclide has an atomic number of 40 + 1 = 41 and a mass number of 50.
Answer 3
Positron emission converts a proton into a neutron, decreasing the atomic number by 1 while keeping the mass number unchanged. The resulting nuclide has an atomic number of 29 – 1 = 28 and a mass number of 35.
Answer 4
Electron capture involves the capture of an electron by a proton, decreasing the atomic number by 1 while keeping the mass number unchanged. The resulting nuclide has an atomic number of 60 – 1 = 59 and a mass number of 90.
Answer 5
Gamma decay involves the emission of a gamma ray photon, which does not affect the atomic number or mass number of the nucleus. The resulting nuclide has the same atomic number of 82 and mass number of 214.
Further Reading on Radioactive Decay
If you are really interested on radioactive decay we invite you to read the following articles: