This kit consists of two pairs of shell-shaped targets and a central holder with adjustment screws and lead absorber.

When a gamma quantum bounces off an electron, its energy loss depends on the scattering angle. Also calculate the force that could be produced and how much effect that would have on a spacecraft.The Compton Effect illustrates the particle nature of gamma radiation. Construct a problem in which you calculate the light pressure on the sail in N/m 2 produced by reflecting sunlight.

Construct Your Own Problem. Consider a space sail such as mentioned in Example 1.

(See Figure 2) He won a Nobel Prize in 1929 for the discovery of this scattering, now called the Compton effect, because it helped prove that photon momentum is given by p=rac=c\. Energy and momentum are conserved in the collision. This phenomenon could be handled as a collision between two particles-a photon and an electron at rest in the material. Around 1923, Compton observed that x rays scattered from materials had a decreased energy and correctly analyzed this as being due to the scattering of photons from electrons. Some of the earliest direct experimental evidence of this came from scattering of x-ray photons by electrons in substances, named Compton scattering after the American physicist Arthur H. Momentum is conserved in quantum mechanics just as it is in relativity and classical physics. Studying this effect, Compton verified that photons have momentum. Energy and momentum are conserved, resulting in a reduction of both for the scattered photon. The Compton effect is the name given to the scattering of a photon by an electron. Gas atoms and molecules in the blue tail are most affected by other particles of radiation, such as protons and electrons emanating from the Sun, rather than by the momentum of photons.įigure 2. Evidently, photons carry momentum in the direction of their motion (away from the Sun), and some of this momentum is transferred to dust particles in collisions. The dust particles recoil away from the Sun when photons scatter from them. Comet tails are composed of gases and dust evaporated from the body of the comet and ionized gas. What most people do not know about the tails is that they always point away from the Sun rather than trailing behind the comet (like the tail of Bo Peep’s sheep). Navy, via Wikimedia Commons)įigure 1 shows a comet with two prominent tails. The blue ionized gas tail is also produced by photons interacting with atoms in the comet material. Particles of dust are pushed away from the Sun by light reflecting from them. Dust emanating from the body of the comet forms this tail. The tails of the Hale-Bopp comet point away from the Sun, evidence that light has momentum. Figure 1 shows macroscopic evidence of photon momentum.įigure 1. In fact, photon momentum is suggested by the photoelectric effect, where photons knock electrons out of a substance. (Maxwell and others who studied EM waves predicted that they would carry momentum.) It is now a well-established fact that photons do have momentum. Despite photons having no mass, there has long been evidence that EM radiation carries momentum. Particles carry momentum as well as energy. Massive quanta, like electrons, also act like macroscopic particles-something we expect, because they are the smallest units of matter.

A photon interacts as a unit in collisions or when absorbed, rather than as an extensive wave. The quantum of EM radiation we call a photon has properties analogous to those of particles we can see, such as grains of sand. Account qualitatively for the increase of photon wavelength that is observed, and explain the significance of the Compton wavelength.Relate the linear momentum of a photon to its energy or wavelength, and apply linear momentum conservation to simple processes involving the emission, absorption, or reflection of photons.By the end of this section, you will be able to:

Compton effect video