Question

Which of the following processes causes the emission of X-ray? (a) \(\alpha\) -emission (b) \beta-emission (c) \(\beta^{+}\) (Positron emission) (d) electron capture

Short answer

The emission of X-rays is caused by electron capture (d).

Step-by-step solution

Understand X-ray Production

X-rays are high-energy, short-wavelength electromagnetic waves, typically produced when high-speed electrons are decelerated or by electronic transitions within an atom. The processes that involve such activities should be considered for X-ray emission.

Analyze \(\alpha\)-emission

\(\alpha\)-emission involves the emission of helium nuclei from a radioactive atom. This process is more related to the release of particles than high-energy photons, so it does not result in X-ray emission.

Analyze \(\beta\)-emission

\(\beta\)-emission involves an electron (\(\beta^-\)) or a positron (\(\beta^+\)) being emitted from a radioactive nucleus. While this can release a good amount of energy, it is not typically associated with X-ray production; however, secondary processes like Bremsstrahlung can produce X-rays when these particles interact with matter.

Analyze \(\beta^{+}\) (Positron emission)

Positron emission itself would not result in the emission of X-rays. However, when the emitted positron encounters an electron, they may undergo annihilation resulting in the production of two gamma photons, which have even higher energy than X-rays.

Analyze electron capture

Electron capture is a process in which an inner orbital electron is captured by the nucleus. This leads to the creation of a vacancy in an inner shell which is then filled by an electron from a higher energy level, releasing energy often in the form of X-rays.

Choose the Correct Option

Based on the understanding of X-ray production and the aforementioned atomic processes, electron capture (option (d)) is the one that causes the emission of X-rays.

Key concepts

Alpha-Emission

Alpha-emission is a type of radioactive decay where an unstable nucleus emits an alpha particle, which is essentially a helium-4 nucleus composed of two protons and two neutrons. This process results in a new element with an atomic number that's two less and a mass number four less than the original atom.

While alpha particles have high energy, they generally lack the penetrating power to create X-rays. Instead, they travel only a short distance in air or other media before being absorbed. X-rays, conversely, require high-speed electrons or other mechanisms to produce the electromagnetic radiation seen in medical imaging and other applications. Therefore, alpha emission does not contribute to the emission of X-rays.

Beta-Emission

Beta-emission occurs when a neutron in an unstable atom's nucleus decays into a proton, emitting an electron (beta-minus emission) or when a proton decays into a neutron, emitting a positron (beta-plus emission). While these high-speed electrons or positrons emitted from the nuclei carry significant energy, they don't directly produce X-rays.

However, when these particles decelerate upon interaction with matter, such as the surrounding materials or detectors, they can give rise to a secondary type of X-rays through a process called Bremsstrahlung. This makes beta-emission indirectly associated with X-ray production, especially in environments where high-speed beta particles are stopped quickly.

Electron Capture

Electron capture is a process by which an electron from an atom's inner shell is captured by the nucleus, leading to the formation of a neutron from a proton and the emission of a neutrino. The loss of an inner-shell electron leaves a vacancy, which is quickly filled by an electron from a higher energy level.

This transition releases energy in the form of an X-ray photon because the energy difference between electron shells is often in the X-ray region of the electromagnetic spectrum. Thus, electron capture is a key process that can produce X-rays, making it essential in this context.

Bremsstrahlung

Bremsstrahlung, which translates to 'braking radiation' in German, is produced when a charged particle, such as an electron, is decelerated by the electromagnetic field of an atomic nucleus, causing the particle to lose energy in the form of X-ray photons. The greater the deceleration or the closer the encounter with the nucleus, the higher the energy of the emitted X-rays.

Since beta particles emitted during radioactive decay can undergo Bremsstrahlung, materials with high atomic numbers often serve as effective targets to convert their kinetic energy into X-ray photons. That's why lead, with its high atomic number, is frequently used in X-ray production equipment and as shielding to protect against X-rays.

Positron Emission

Positron emission, or beta-plus decay, is a process where a proton inside a nucleus is transformed into a neutron, releasing a positron and a neutrino. The emitted positron is the antimatter counterpart to an electron, and when it encounters an electron, it undergoes annihilation.

During annihilation, the positron and electron destroy each other, and their mass is converted to energy in the form of two gamma-ray photons, not X-rays. These gamma rays have even higher energy levels than X-rays. While positron annihilation doesn't directly produce X-rays, in some scenarios, the gamma rays can interact with electrons in matter, resulting in a cascade that may include the production of X-ray photons.