X-RAYS

Back to IB PHYSICS > EM WAVES OPTION =X-RAYS= [|HOW X-RAYS ARE CREATED] - simulation from Colorado [|STORY ABOUT HISTORICAL X-RAY MACHINE] - BBC News website Outline the experimental arrangement for the production of X-rays. X-RAYS: Very high energy electromagnetic waves of frequency around 10 18 Hz and wavelength around 10 -10 m. More energetic X-rays are called ‘hard’. X-RAY PRODUCTION: Thermionic electrons accelerated by a PD collide with a metal target causing excited electrons in the target and emission of X-ray photons.
 * WAVES AND SOURCES || OPTICAL INSTRUMENTS || TWO-SOURCE INTERFERENCE || DIFFRACTION GRATING || X-RAYS || THIN-FILM INTERFERENCE ||

A Coolidge tube is sufficient. Students should understand how the intensity and hardness of the X-ray beam are controlled. Draw and annotate a typical X-ray spectrum.

Students should be able to identify the continuous and characteristic features of the spectrum and the minimum wavelength limit.

CHARACTERISTIC PEAKS IN X-RAY SPECTRUM: Discrete frequencies of X-ray photons emitted by the target which are characteristic of the material of the particular target. The values are unaffected by the accelerating PD of the X-ray tube.

CONTINUOUS X-RAY SPECTRUM: X-rays resulting from the deceleration of the incident electrons can take a continuous range of wavelengths up to a maximum frequency corresponding to the accelerating PD of the X-ray tube.

MINIMUM WAVELENGTH: Corresponds to maximum energy (frequency) of X-ray photon produced by a particular accelerating PD.

Explain the origins of the features of a characteristic X-ray spectrum.

Solve problems involving accelerating potential difference and minimum wavelength.



X-ray diffraction
Explain how X-ray diffraction arises from the scattering of X-rays in a crystal. This may be illustrated using 3 cm equipment.

X-RAY DIFFRACTION: When X-rays reflect from different planes in a crystal, they constructively interfere for certain angles of incidence from which the plane spacing can be deduced. Equally, a crystal of known dimensions allows us to measure the wavelength of X-rays.

[|SIMULATION OF X-RAY DIFFRACTION] using the Bragg equation

Derive the Bragg scattering equation.

BRAGG EQUATION: Describes the formation of maxima by constructive interference of waves reflecting off adjacent crystal planes. The incident angle is measured from the surface, not the normal.



Outline how cubic crystals may be used to measure the wavelength of X-rays.

Outline how X-rays may be used to determine the structure of crystals. Students should be aware of the fact that the structure of DNA was discovered by means of X-ray diffraction. Solve problems involving the Bragg equation.