Braggs Law The braggs British physicists William Henry Bragg n2= 2dsine (1862-1942) and William Lawrence bragg where n= order of diffraction (1890-1971)won Nobel Phvsical Prize in 1915 2=Xray wavelength due to their achievements on the structure Analysis via X'ray d= spacing between layers of atom 0 angle of diffraction Braggs Law is the fundamental law of x crvst Generation of X-rays X-ray Emission Spectrum knock inner core electrons are produced by thermionic emission from a W filament and are accelerated by a large potential difference innermost shell (K) I. the high energy electrons (? 50 kev)bombard a metal these vacancies are rapidly filled by electronic transitions from target (usually Cu, but can also be Mo the other orbitals not all transitions are possibl X-rays are generated by eraction between electron Ithe wavelengths are characteristic of the nd targe -target element 一 Heated filament 15418A PD? 50kV M anode Copper anode igh intensity X-rays can be generated using a part on X-ray generation Using a Syne Synchrotron Radiation resolution much quicker data collection. emit radiation tangentially. A particular wavelength can be lected from the continuous spectrum of X-rays generated. Synchrotron radiation: tunable Storage r3 nl = 2dsinq where n Þ order of diffraction l Þ X-ray wavelength d Þ spacing between layers of atom q Þ angle of diffraction Bragg's Law is the fundamental law of x-ray crystallography. Bragg's Law The Braggs British physicists William Henry Bragg (1862~1942) and William Lawrence Bragg (1890~1971) won Nobel Physical Prize in 1915 due to their achievements on the Structure Analysis via X-ray. Generation of X-rays Copper anode Heated tungsten filament electrons X-rays - + cathode anode PD ? 50 kV ß electrons are produced by thermionic emission from a W filament and are accelerated by a large potential difference ß the high energy electrons (? 50 keV) bombard a metal target (usually Cu, but can also be Mo) ß X-rays are generated by the interaction between electrons and target X-ray Emission Spectrum ßupon collisions the high energy electrons can knock inner core electrons from the target atoms, leaving vacancies in the innermost shell (K) ß these vacancies are rapidly filled by electronic transitions from the other orbitals not all transitions are possible the wavelengths are characteristic of the target element Intensity l Wavelength c Kb2 Kb1 Ka1 Ka2 Copper anode: Ka 1.5418 Å Kb 1.3922 Å K M L Ka2 Ka1 Kb1 Kb2 X-ray Generation Using a Synchrotron High intensity X-rays can be generated using a particle accelerator such as a synchrotron: charged particles (electron or positrons) are accelerated round a circle and emit radiation tangentially. A particular wavelength can be selected from the continuous spectrum of X-rays generated. Synchrotron radiation: ß tunable ß intense X-rays X-rays beam Synchrotron Radiation More intense X-rays at shorter wavelengths mean higher resolution & much quicker data collection