Nuclear Physics

## Big Picture

Nuclear physics studies the interactions between subatomic particles of matter. Atoms are made up of protons, neutrons, and electrons. In turn, protons and neutrons are made up of quarks. Radiation is the release of energy from decaying particles. Nuclear energy, generated from fusion and fission, release large amounts of energy.

## Key Terms

Nuclear Binding Energy: The mass of a nucleus is less than the sum of the masses of its constituents (neutrons and protons). This difference in mass is stored as nuclear binding energy which holds the nucleus (the neutrons and protons) together. To break a nucleus apart, we must overcome this energy.

Nuclear Fission: A nuclear reaction in which the nucleus of an atom is split into smaller parts.

Nuclear Fusion: A nuclear reaction in which two or more nuclei are joined together.

Braking Radiation: Radiation produced when a charged particle slows down due to another charged particle.

Compton Scattering: The scattering of X-rays and gamma rays when they go through matter.

Radiation occurs when particles or electromagnetic waves have enough energy to remove electrons from a substance (either an atom or a molecule), thus ionizing it.

• Alpha radiation, α, is when an alpha particle is emitted. Alpha particles are helium atoms, 42He, that due to their large size, move slowly and are stopped by a few inches of air, skin, or paper.
• Beta radiation, β, is when a beta particle is emitted. Beta particles are electrons that move faster than alpha particles and, because of their small size, must be stopped by a few feet of air, aluminum or other light metals.
• Positron emission, $$β^+$$, is when a positive charge (positron) is emitted, while electron emission, $$β^-$$ or $$e^-$$, is when a negative charge (electron) is emitted.
• Gamma radiation, γ, is when gamma rays are emitted. Gamma rays are photons--invisible, high energy light. It travels fastest and must be stopped by a sheet of lead.

changing electric and magnetic fields that are oriented in directions perpendicular to the direction of travel. Electromagnetic radiation is categorized by its wavelength, ranging from radio waves of wavelength $$10^8$$ meters to gamma rays of wavelength $$10^{-16}$$ meters. Below is an illustration showing the divisions in the electromagnetic spectrum.

Smoke Detectors: Americium-241 decays and releases alpha particles that break up air molecules into ions that complete an electrical circuit. These ions are attracted to smoke particles, so when there is a fire, the circuit is broken, setting off the fire alarm.

Measuring aluminum thickness: Since beta particles are generally stopped by aluminum, manufactures of thin aluminum foil can measure the thickness of the foil by measuring how much beta radiation passes through.

Cancer treatments: Beta radiation is especially damaging to cells that are in the process of dividing, and since cancer cells divide much more rapidly than normal cells, beta radiation can be used to effectively kill cancer cells.

Sterilizing equipment: Gamma radiation can kill bacteria and other microorganisms. It can be used to sterilize delicate equipment without subjecting it to high temperatures or chemicals.

## Important Equations

$$E = mc^2$$

E - energy

m - mass

c - speed of light