Difference Between Positron Emission and Electron Capture

Key Difference – Positron Emission vs Electron Capture
 

Positron emission and electron capture and  are two types of nuclear processes. Although they result in changes in the nucleus, these two processes take place in two different ways. Both these radioactive processes occur in unstable nuclei where there are too many protons and fewer neutrons. To solve this problem, these processes result in changing a proton in the nucleus into a neutron; but in two different ways. In positron emission, a positron (opposite of an electron) is also created in addition to the neutron. In electron capture, the unstable nucleus captures one of the electrons from one of its orbitals and then produces a neutron. This is the key difference between positron emission and electron capture.

What is Positron Emission?

Positron emission is a type of radioactive decay and a sub-type of beta decay and is also known as beta plus decay (β⁺ decay). This process involves the conversion of a proton into a neutron inside a radionuclide nucleus while releasing a positron and an electron neutrino (ν_e). Positron decay typically occurs in large ‘proton-rich’ radionuclides, because this process decreases the proton number relative to the neutron number. This also results in nuclear transmutation, producing an atom of a chemical element into an element with an atomic number which is lower by one unit.

What is Electron Capture?

Electron capture (also known as K-electron capture, K-capture, or L-electron capture, L-capture) involves absorption of an inner atomic electron, usually from its K or L electron shell by a proton-rich nucleus of an electrically neutral atom. In this process, two things occur simultaneously; a nuclear proton changes to a neutron after reacting with an electron which falls into the nucleus from one of its orbitals and the emission of an electron neutrino. In addition, a lot of energy is released as gamma-rays.

What is the difference between Positron Emission and Electron Capture?

Representation by an equation:

Positron Emission:

An example of a positron emission (β⁺ decay) is shown below.

Notes:

• The nuclide that decays is the one on the left-hand side of the equation.
• The order of the nuclides on the right-hand side can be in any order.
• The general way of representing a positron emission is as above.
• The mass number and atomic number of the neutrino are zero.
• The neutrino symbol is the Greek letter “nu.”

Electron Capture:

An example of electron capture is shown below.

Notes:

• The nuclide that decays is written on the left-hand side of the equation.
• The electron must also be written on the left-hand side.
• A neutrino is also involved in this process. It is ejected from the nucleus where the electron reacts; therefore it is written on the right-hand side.
• The general way of representing an electron capture is as above.

Examples of Positron Emission and Electron Capture:

Positron Emission:

Electron Capture:

Characteristics of Positron Emission and Electron Capture:

Positron Emission: Positron decay can be considered as the mirror image of beta decay. Some other special features include

• A proton becomes a neutron as a result of a radio-active process that occurs inside the nucleus of an atom.
• This process results in the emission of a positron and a neutrino which go zooming off into space.
• This process leads to the reduction of the atomic number by one unit, and the mass number remains unchanged.

Electron Capture: Electron capture does not occur in the same way as the other radio-active decays such as alpha, beta, or position. In electron capture, something enters the nucleus, but all the other decays involve shooting something out of the nucleus.

Some other significant features include

• An electron from the closest energy level (mostly from K-shell or L-shell) falls into the nucleus, and this causes a proton to become a neutron.
• A neutrino is emitted from the nucleus.
• The atomic number goes down by one unit, and mass number remains unchanged.

Definitions:

Nuclear transmutation:

An artificial radioactive method of transforming one element/isotope into another element/isotope. Stable atoms can be transformed into radioactive atoms by bombardment with high-speed particles.

Nuclide:

a distinct kind of atom or nucleus characterized by a specific number of protons and neutrons.

Neutrino:

A neutrino is a subatomic particle with no electric charge