Inelastic scattering

Tiny bits hit each other. Sometimes they bump and change. They might lose energy during a bump. This happens when bits strike a nucleus. The nucleus can become unstable. It might then send out radiation. This can be a tiny bit called a proton. This also happens when bits hit a molecule. Energy moves between the bits. It can make a molecule spin or shake. This helps us see how things work. It is a very busy world of tiny bumps.

Tiny bits of matter are always bumping into each other. Sometimes, these bumps change the bits. This is called inelastic scattering. In this way, the bits change their internal state. This often means they lose some power, or kinetic energy.

One way this happens is with light. A photon is a tiny bit of light. In Raman scattering, a photon hits matter. The photon can change its color. It might shift toward red. This happens when it gives power to the matter. This is called Stokes Raman scattering. It can also shift toward blue. This is called anti-Stokes Raman scattering.

Neutrons also do this. A neutron is a tiny bit of matter. It can hit a nucleus, which is the center of an atom. The hit can make the nucleus unstable. This is called an excited state. The nucleus might then let out radiation to stay safe. It might send out a proton or a gamma ray.

This also happens with molecules. Molecules are groups of atoms. When they bump, energy moves around. It can make a molecule spin or shake. This is a common way for energy to move.

Tiny particles are always bumping into each other. Sometimes these bumps change the particles in a special way. This is called inelastic scattering. In this process, the internal state of a particle changes. This often means the particle loses some kinetic energy. Kinetic energy is the energy of motion.

There are many ways this works. When a photon hits matter, it can change color. This is known as Raman scattering. A photon is a tiny bit of light. In Stokes Raman scattering, the light shifts toward red. The photon gives some energy to the matter. In anti-Stokes Raman scattering, the light shifts toward blue. This happens when the matter gives energy to the photon.

Scientists have used these bumps to learn big secrets. Deep inelastic scattering involves electrons hitting protons. This gave the first direct evidence for quarks. Quarks are tiny parts of matter. Electrons also do something called Compton scattering. This happens when a high-energy photon hits a weakly bound electron. The photon transfers energy to the electron.

Neutrons also show us how energy moves. A neutron can strike a nucleus. This can put the nucleus into an excited state. An excited state is an unstable and short-lived state. The nucleus might then emit radiation to become stable again. It may release a proton, a beta particle, or a gamma ray. The nucleus might even recoil in the opposite direction.

These bumps happen with molecules too. Molecules are groups of atoms. In a molecular collision, energy moves between different modes. It can move from moving in a straight line to spinning. It can also move into vibrational modes. Vibrational modes are when the molecule shakes. If the energy change is very small, it is called quasielastic scattering.

In the fields of chemistry, nuclear physics, and particle physics, scientists study how particles interact. One important way they interact is through inelastic scattering. This is a process where the internal states of a particle or a system change after a collision. In many cases, this means the kinetic energy of the incident particle is not conserved. Kinetic energy is the energy an object has because of its motion. This differs from elastic scattering, where kinetic energy remains the same.

Inelastic scattering works through a transfer of energy between different parts of a system. When particles collide, energy can move from motion into internal changes. This might change the way a particle spins or vibrates. In relativistic collisions, a transition from one type of particle to another can occur. These are called inelastic even if the outgoing particles have the same kinetic energy as the incoming ones. Sometimes, a macroscopic observer only sees inelastic scattering because they cannot see all the moving parts. This happens when a collision is actually elastic at a microscopic level, but the observer only sees a subset of the degrees of freedom.

Different particles show unique types of inelastic scattering. When a photon, which is a particle of light, hits matter, it can undergo Raman scattering. This process shifts the frequency of the photon toward red or blue. In Stokes Raman scattering, the photon transfers part of its energy to the matter. This adds to the internal energy of the matter and creates a red shift. Conversely, anti-Stokes Raman scattering occurs when the matter transfers internal energy to the photon. This causes a blue shift in the light.

Electrons also participate in specific inelastic processes. One notable example is Compton scattering. This occurs when a high-energy photon collides with a weakly bound electron. During this collision, the photon transfers energy to the electron. Another process is called inverse Compton scattering. This happens when an electron with relativistic energy collides with a photon in the infrared or visible spectrum. In this case, the electron gives its energy to the photon.

Neutrons provide a way to study the very center of atoms. Whether a neutron undergoes elastic or inelastic scattering depends on its speed. It can be a fast neutron, a thermal neutron, or something in between. The outcome also depends on the specific nucleus it strikes and its neutron cross section. In inelastic scattering, the neutron interacts with the nucleus to change the system's kinetic energy. This can activate the nucleus by putting it into an excited, unstable, and short-lived energy state. To return to a stable ground state, the nucleus may quickly emit radiation. This radiation can include alpha, beta, gamma, or protons. The particles scattered in this reaction might also cause the nucleus to recoil in the opposite direction.

History shows how these collisions reveal the building blocks of our world. Scientists used deep inelastic scattering of electrons from protons to make a major discovery. This provided the first direct evidence for the existence of quarks. Quarks are the fundamental particles that make up protons and neutrons. In other studies, such as gas electron diffraction (GED) or transmission electron diffraction, scientists use high-energy electrons. Because the energy is so high, they can often ignore the contribution of inelastic electron scattering.

Finally, inelastic scattering is very common during molecular collisions. Any collision that leads to a chemical reaction is considered inelastic. However, scientists reserve the specific term "inelastic scattering" for collisions that do not result in a reaction. In these moments, energy transfers between the translational mode and other modes. The translational mode is the straight-line kinetic energy of the molecule. The energy can move into rotational modes or vibrational modes, where the molecule shakes. If the transferred energy is very small compared to the incident energy, it is called quasielastic scattering.