In nuclear radiation, gamma rays (γ-rays) are a form of electromagnetic radiation. As such, they are characterised by which combination of mass and electric charge?

Introduction / Context:
Radioactive substances can emit different types of radiation, including alpha particles, beta particles and gamma rays. Understanding the nature of each type is crucial for nuclear physics, radiation protection and medical imaging. This question focuses on gamma rays and asks you to identify whether they possess mass and electric charge.

Given Data / Assumptions:

• Gamma rays are at the high-energy end of the electromagnetic spectrum.
• Electromagnetic radiation includes radio waves, microwaves, infrared, visible light, ultraviolet, X rays and gamma rays.
• Electromagnetic waves are understood as oscillating electric and magnetic fields.
• We consider rest mass and net electric charge for each type of radiation.

Concept / Approach:
Gamma rays are photons, which are the quanta of the electromagnetic field. Photons have no rest mass and no electric charge. Although photons carry energy and momentum and can exert pressure or transfer energy to matter, they do not have mass in the same sense as particles like electrons, protons or neutrons. They also do not carry electric charge, which is why they are not deflected by electric or magnetic fields in the same way as charged particles. This distinguishes gamma rays from alpha particles (which have mass and positive charge) and beta particles (which have mass and negative or positive charge).

Step-by-Step Solution:
Step 1: Recall that gamma rays are a type of electromagnetic radiation, like X rays and visible light.Step 2: Recognise that electromagnetic radiation is composed of photons.Step 3: Remember that photons have zero rest mass and are electrically neutral, carrying no net charge.Step 4: Note that photons still carry energy E and momentum p, but this does not imply rest mass or charge.Step 5: Compare this with other nuclear emissions: alpha particles (helium nuclei) have mass and positive charge, beta particles (electrons or positrons) have mass and negative or positive charge.Step 6: Conclude that gamma rays have neither mass nor electric charge.

Verification / Alternative check:
In experiments with electric and magnetic fields, gamma rays are not deflected, indicating that they carry no electric charge. In contrast, beta particles are deflected strongly and alpha particles are deflected moderately, consistent with their charges and masses. Textbooks consistently state that photons are massless (in the rest-mass sense) and neutral. The role of gamma rays in medical imaging, such as PET scans or gamma cameras, also relies on their ability to penetrate tissue similarly to X rays, again behaving as uncharged, massless quanta of electromagnetic energy.

Why Other Options Are Wrong:
Option A claims gamma rays have electric charge but no mass, which would cause them to be deflected in electric and magnetic fields; this does not match observations. Option C says they have both mass and charge, again contradicting the properties of photons. Option D suggests they have mass but no charge, which is more like neutrons in nuclear physics, not gamma rays. None of these match the well-established understanding of gamma rays as massless, uncharged photons.

Common Pitfalls:
Students sometimes mix up gamma rays with alpha or beta particles because all three are emitted from radioactive nuclei. Others may think that because gamma rays have energy, they must have mass, misunderstanding the distinction between mass and energy in relativity. To avoid confusion, remember that gamma rays are electromagnetic waves (photons) and share the same massless, chargeless nature as visible light, differing primarily in their much higher energy and frequency.

Final Answer:
Gamma rays are electromagnetic photons that have neither mass nor electric charge.