Video: Recalling the Masses of Forms of Radiation

Which of the following radiation emissions has no mass? [A] Proton [B] Neutron [C] Gamma ray [D] Beta particle [E] Alpha particle.

02:37

Video Transcript

Which of the following radiation emissions has no mass? A) Proton, B) Neutron, C) Gamma ray, D) Beta particle, or E) Alpha particle.

Mass is a very common property. Pretty much everything in the universe has mass. But what exactly is mass? If something has mass, gravity affects it. Objects with mass attract other objects with mass via gravitational attraction. But the gravitational force is very weak, so we need a lot of mass in order to feel it directly.

The mass of an object plays a much more obvious role when we’re dealing with momentum and collisions. So, mass is a very fundamental part of how particles behave. But not all particles have mass. Protons and neutrons have mass, about the same mass as one twelfth the mass of a carbon-12 atom. This should come as no surprise because carbon-12 atoms contain six protons and six neutrons each. They also contain six electrons. But electrons, even though they have mass, don’t have as much as protons or neutrons.

So, answers A and B, proton and neutron, are incorrect answers because they do have mass. A beta particle is just a high-energy electron. The mass of the electron is about one two thousandths of the mass of a proton or a neutron. While relatively tiny, the mass of the electron is still mass. So, a beta particle has mass, and so is an incorrect answer.

On the other hand, a gamma ray is an electromagnetic wave, which comes in individual energy packets called photons. Even though electromagnetic waves, otherwise known as light, have energy, they don’t have any mass. So, gamma ray is our correct answer.

Our other alternative answer, the alpha particle, definitely does have mass because an alpha particle consists of two protons and two neutrons. It’s sometimes represented as a naked helium nucleus. So, if protons and neutrons have mass, an alpha particle definitely does too. So, of the five radiation emissions given, the one that has no mass is the gamma ray.

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