《固体物理学》课程教学课件（PPT讲稿）Chapter 2 Wave Diffraction & the Reciprocal Lattice（supplement - Review & Overview of X-Rays）

2-1 supplement:Review Overview of X-Rays Their Properties X-Rays were discovered in 1895 by German physicist Wilhelm Conrad Rontgen.They were called X-Rays because their nature was unknown at the time.He was awarded the Physics Nobel Prize in 1901. The 1st X-Ray photograph taken was of Rontgen's wife's left hand. Wilhelm Conrad Rǒntgen(1845-1923) Bertha Rontgen's Hand 8 Nov,1895

• X-Rays were discovered in 1895 by German physicist Wilhelm Conrad Röntgen. They were called X-Rays because their nature was unknown at the time. He was awarded the Physics Nobel Prize in 1901. Wilhelm Conrad Röntgen (1845-1923) Bertha Röntgen’s Hand 8 Nov, 1895 2-1 supplement：Review & Overview of X-Rays & Their Properties The 1st X-Ray photograph taken was of Röntgen’s wife’s left hand

Review of X-Ray Properties X-Rays are invisible,highly penetrating Electromagnetic Radiation of much shorter wavelength (higher frequency)than visible light.Wavelength ()frequency (v)ranges for X-Rays: 10-8m~≤λ~≤1011m 3X1016Hz~≤V~≤3X1019Hz ultraviolet shortwave gamma X-rays rays infrared radar FM TV AM rays rays 104 10 210”10 10 0、1021 102 10 Wavelength (meters) Visible Light 400 500 600 700 Wavelength(nanometers)

Review of X-Ray Properties • X-Rays are invisible, highly penetrating Electromagnetic Radiation of much shorter wavelength (higher frequency) than visible light. Wavelength (λ) & frequency (ν) ranges for X-Rays: 10-8 m ~ ≤ λ ~ ≤ 10-11 m 3 × 1016 Hz ~ ≤ ν ~ ≤ 3 × 1019 Hz

2-2 supplemnet X-Ray Production Visible light photons,X-Ray photons,essentially all other photons are produced by the movement of electrons in atoms. We know from Quantum Mechanics that electrons occupy energy levels,or orbitals,around an atom's nucleus. If an electron drops to a lower orbital (spontaneously or due to some external perturbation)it releases some energy This released energy is in the form of a photon The photon energy depends on how far in energy the electron dropps between orbitals

2-2 supplemnet X-Ray Production • Visible light photons, X-Ray photons, & essentially all other photons are produced by the movement of electrons in atoms. • We know from Quantum Mechanics that electrons occupy energy levels, or orbitals, around an atom's nucleus. • If an electron drops to a lower orbital (spontaneously or due to some external perturbation) it releases some energy. This released energy is in the form of a photon • The photon energy depends on how far in energy the electron dropps between orbitals

Schematic Diagram of Photon Emission Incoming particles excite an atom by promoting an electron to a higher energy orbit.Later,the electron falls back to the lower orbit,releasing a photon with energy equal to the energy difference between the two states: hv=△E Remember that this figure is a Particles How Atoms Emit Light schematic“cartoon”only,shown to crudely illustrate how atoms emit light when one of the electrons transitions from one level to another.It gives the impression that the electrons in an atom are in Bohr- like orbits around the nucleus.From Quantum Mechanics,we know that 1.A collision with a moving particle this picture is not valid,but the electron axcites the atom 2. This causes an electron to jump to a wavefunction is spread all over the higher energy level. 3.The electron falls back to it's original enerey level.releasing the atom.So,don't take this figure literally! extra energy in the form of a light Light photon Photon

Remember that this figure is a schematic “cartoon” only, shown to crudely illustrate how atoms emit light when one of the electrons transitions from one level to another. It gives the impression that the electrons in an atom are in Bohr￾like orbits around the nucleus. From Quantum Mechanics, we know that this picture is not valid, but the electron wavefunction is spread all over the atom. So, don’t take this figure literally! Schematic Diagram of Photon Emission Incoming particles excite an atom by promoting an electron to a higher energy orbit. Later, the electron falls back to the lower orbit, releasing a photon with energy equal to the energy difference between the two states: hν = ΔE

X-Ray Tubes X-Rays can be produced in a highly evacuated glass bulb,called an X-Ray tube,that contains two electrodes:an anode made of platinum,tungsten,or another heavy metal of high melting point,a cathode. When a high voltage is applied between the electrodes, streams of electrons (cathode rays)are accelerated from the cathode to the anode produce X-Rays as they strike the anode. Evacuated Glass Bulb Cathode Anode

Evacuated Glass Bulb Anode Cathode • X-Rays can be produced in a highly evacuated glass bulb, called an X-Ray tube, that contains two electrodes: an anode made of platinum, tungsten, or another heavy metal of high melting point, & a cathode. When a high voltage is applied between the electrodes, streams of electrons (cathode rays) are accelerated from the cathode to the anode & produce X-Rays as they strike the anode. X-Ray Tubes

Monochromatic Broad Spectrum X-rays X-Rays can be created by bombarding a metal target with high energy (>1e)electrons. Some of these electrons excite other electrons from core states in the metal,which then recombine, producing highly monochromatic X-Rays.These are referred to as characteristic X-Ray lines. Other electrons,which are decelerated by the periodic potential inside the metal,produce a broad spectrum of X-Ray frequencies. Depending on the diffraction experiment,either or both of these X-Ray spectra can be used

• X-Rays can be created by bombarding a metal target with high energy (> 104 eV) electrons. • Some of these electrons excite other electrons from core states in the metal, which then recombine, producing highly monochromatic X-Rays. These are referred to as characteristic X-Ray lines. • Other electrons, which are decelerated by the periodic potential inside the metal, produce a broad spectrum of X-Ray frequencies. • Depending on the diffraction experiment, either or both of these X-Ray spectra can be used. Monochromatic & Broad Spectrum X-rays

X-Ray Absorption The atoms that make up our You will never see body's tissue absorb visible light something like this photons very well.The energy with Visible Light!! level of the photon fits with various energy differences between electron states. Radio waves don't have enough energy to move electrons between orbitals in larger atoms,so they pass through most materials. X-Ray photons also pass through most things,but for the X-Rays opposite reason:They have too much energy

• The atoms that make up our body’s tissue absorb visible light photons very well. The energy level of the photon fits with various energy differences between electron states. • Radio waves don't have enough energy to move electrons between orbitals in larger atoms, so they pass through most materials. • X-Ray photons also pass through most things, but for the opposite reason: They have too much energy. You will never see something like this with Visible Light!!  X-Rays X-Ray Absorption

Generation of X-rays(K-Shell Knockout) An electron in a higher orbital falls to the lower energy level, releasing its extra energy in the form of a photon.It's a large drop, so the photon has high energy;it is an X-Ray photon. Another schematic cartoon diagram, not to be taken literally! A“fee”electron collides with a tungsten atom, knocking an electron out of a lower orbital.A higher orbital electron fills the empty position,releasing its excess energy as an X-Ray Photon e2002Hew5 tutterk图

An electron in a higher orbital falls to the lower energy level, releasing its extra energy in the form of a photon. It's a large drop, so the photon has high energy; it is an X-Ray photon. A “free” electron collides with a tungsten atom, knocking an electron out of a lower orbital. A higher orbital electron fills the empty position, releasing its excess energy as an X-Ray Photon Another schematic cartoon diagram, not to be taken literally!  Generation of X-rays (K-Shell Knockout)