Question

What do we mean when we say a nucleus has undergone an electron capture process? What type of electron is captured by the nucleus in this process?

Short answer

When a nucleus undergoes an electron capture process, it absorbs an inner electron (usually from the K-shell or L-shell), leading to the transformation of a proton into a neutron and a decrease in the atomic number by one. The mass number, however, remains unchanged. In this process, the nucleus typically captures electrons from the K-shell, which is the shell closest to the nucleus, although occasionally electrons from the L-shell can be captured as well.

Step-by-step solution

Define Electron Capture Process

Electron capture is a nuclear process in which an atom's nucleus absorbs an inner electron (usually from the K-shell or L-shell), resulting in the transformation of a proton into a neutron. When a nucleus undergoes electron capture, the atom's atomic number decreases by one while the mass number remains unchanged.

Identify the Type of Electron Involved

In electron capture, it is typically the innermost electrons that are captured by the nucleus. These electrons belong to the K-shell, which is the shell closest to the nucleus. Occasionally, electrons from the L-shell (the second shell) can also be captured, but this is less common.

Briefly explain the outcome of the electron capture process

After the electron capture process, the daughter nuclide usually ends up in an excited state. This means that it has more energy than its ground state, or lowest energy level. To return to this ground state, the daughter nuclide emits gamma rays, which are high-energy electromagnetic radiation. To summarize, during electron capture, an atom's nucleus captures an inner electron, typically from the K-shell, and transforms a proton into a neutron. This process results in a decrease in the atomic number by one, but the mass number remains unchanged.

Key concepts

Nuclear Process

A nuclear process is a transformation that occurs within the nucleus of an atom. Different from chemical reactions, which involve the exchange or sharing of electrons, nuclear processes affect the particles inside the nucleus – protons and neutrons. There are various types of nuclear processes, such as radioactive decay, nuclear fusion, and nuclear fission. In the case of electron capture, the process involves the absorption of an inner electron by the nucleus. This results in a transformation where a proton is converted into a neutron. The operation of these processes often leads to changes in the basic properties of the atom, like its atomic number and energy states, making them unique and fascinating from both a scientific and practical perspective.

Understanding nuclear processes is essential in physics and engineering, as they lay the foundation for explaining how nuclear reactions power stars, how energy is released in nuclear reactors, and many medical applications, including cancer treatments.

Atomic Number

The atomic number of an element is a fundamental property, denoted by the symbol \( Z \). It represents the number of protons in the nucleus of an atom. This number defines the identity of an element, and it is what sets one element apart from another. For example, hydrogen has an atomic number of 1, meaning it has one proton, while helium has an atomic number of 2, indicating two protons.

In electron capture, the atomic number decreases by one because a proton in the nucleus is converted into a neutron after capturing an inner electron. Despite this transformation, the overall mass number of the atom remains unchanged because a neutron and a proton both contribute approximately the same mass. This decrease in atomic number results in the transmutation of the element, meaning it turns into a different element on the periodic table.

Gamma Rays

Gamma rays are a form of electromagnetic radiation, similar to X-rays, but with much higher energy. They have no mass and no charge, allowing them to penetrate materials more deeply than other types of radiation like alpha or beta particles. Gamma rays are often emitted by atoms in an excited state after a nuclear process, such as electron capture.

When a nucleus captures an electron and a proton is converted to a neutron, the resulting daughter nuclide may be left in an excited state. To reach its lowest energy level, or ground state, it releases excess energy in the form of gamma rays. These emissions are crucial in various applications, such as in medical imaging and treatments, but they also require careful handling due to their deeply penetrating nature and potential to cause damage to living tissues.

K-shell

The K-shell, also known as the 1st energy level or shell, is the closest energy level to an atom’s nucleus. It can hold up to two electrons. This proximity to the nucleus means electrons in the K-shell are strongly attracted to its positive charge. In the process of electron capture, an atom's nucleus commonly absorbs an electron from this shell.

When this inner electron is captured, the change can effectively redevelop the atom's nucleus, turning a proton into a neutron. This alteration affects the atom's atomic number, as mentioned before, resulting in a new element formation in the periodic table. Despite their involvement in changes at the atomic level, electrons from the K-shell are an essential tool in understanding the structural identity and transformations of atoms during nuclear processes.