Xray sources Purpose of Xray diffraction phase composition

X-ray sources

Purpose of X-ray diffraction phase composition of samples (qualitative and quantitative) lattice parameter determination measurement of residual stresses determination of crystal structures measurement of texture/preferred orientation + in-situ methods

https: //en. wikipedia. org/wiki/Electromagnetic_spectrum#/media/File: EM_Spectrum_Properties_edit. svg What are X-rays? part of the el. -mag. spectrums between 1 and 120 ke. V

Properties of X-rays wave – particle – duality: wave: M. v. Laue, W. Friedrich, F. Knipping (1912): diffraction by crystals particle: A. H. Compton (1923): anelastic scattering by electrons index of refraction slightly less than unity, i. e. vacuum is optically dense high energy, → damage of biological tissue (ionising) performing experiments: - regulated by the German radiation safety law (Strl. Sch. G) - requires special safety precautions „In the frame of radiation safety all unnecessary radiation exposure for humans and environment needs to be avoided. “

How are X-rays created? - Acceleration of charged particles: - mostly fast electrons, being decelerated in matter (atom cores) and thereby emitting energy in form of X-ray quants Bremsstrahlung (continuous spectrum) - ionisation and de-ionisation through interaction of fast electrons with the electron shell of atoms charakteristic X-rays Fermis golden rule

Applications of X-rays - tomographic imaging based on absorption of X-rays by matter - investigation of crystalline matter via diffraction and interference (wavelength of radiation matches distances of the diffraction grating) - radiation therapy (Onkology) - elemental analysis of matter (X-ray fluorescence spectroscopy) - sterilisation All applications require appropriate X-ray sources!

spiral galaxy M 101 – Chandra X-ray Telescope

Sun – Yohkoh Solar Observatory

Z-Machine (Sandia Labs, NM, USA)

X-ray sources for laboratories William D. Coolidge [1873 -1975]

X-ray sources for laboratories → application in diffractometers

X-ray sources: sealed glass X-ray tube

X-ray sources – main components - evacuated (glass) cylinder - cathode (negative pole): - consists of filament and focussing element, creates electrons - filament: tungsten wire, heated via passage of electrical current - induced by thermal energy, electrons are ejected from the wire (thermoionic em. ) - electrons will be focussed and accelerated by the cathode - voltage controls the acceleration of electrons, filament current their number - anode (positive pole): - defines characteristic part of radiation - needs to be cooled to dissipate heat generated during electron bombardment

X-ray sources – main components operation of the tube is controlled by current and voltage: - m. A (tube current): controls the number of electrons hitting the anode -> X-ray photons (= intensity), direct proportionality - k. V (tube voltage): controls the kinetic energy of electrons when travelling to the anode (requires a minimum to initiate ionisation); is a measure of efficiency of photon ejection/electron radiation from X-ray tubes is partially polarised

X-ray sources – main components Safety Shutter - most important part of the tube housing - opens only when safety circuits are closed - can save your life while working with X-rays

geometry of the anode

anode materials tube parameters: - max. working voltage: 60 k. V - max. filament current: 3. 8 A - Power: ~ 2000 W - Be – window: 0. 25 mm thickness - > 3. 5 l cooling water/min Anodenmaterial: - Cu: standard, first choice for most cases [except Co, Fe, Mn, W] - W: Laue – method/white beam (high penetration depth, wide spectrum) - Co: Fe-containing samples, reduces fluorescence [except Mn, Cr, V] - Mo: heavily absorbing materials, measurement up to high hkl [except Y, Sr, Rb] - Fe: mainly for minerals [except Cr, V, Ti] - Cr: materials with large lattice parameters, residual stresses in ferritic steels - Ag: recording pair distribution functions (when no synchrotron is available) - + weitere

anode material - fluorescence http: //xray. tamu. edu/pdf/notes/source_selection. pdf

anode material - fluorescence

X-ray sources for laboratories Why rotating anode? + higher intensity + no water cooling - higher maintenance effort - higher deterioration

X-ray tube output Bremsstrahlung: - no collisions of electrons - electron reactes with the Coulomb field of the atom core - involves a change of direction and speed of motion of the electron - change in energy via emission of X-ray photons - spectrum is continuous, since interaction can take place at all loci, at all distances and all angles of incidence A … constant Z … atomic number (anode) V … acceleration voltage i … electron current

energy distribution of Bremsstrahlung

X-ray tube output characteristic spectrum: - collision between accellerated and core electrons - ejection of bound electrons from the electron shell (conservation of energy and momentum) - excited atoms reduce their energy by motion of a higher shell eletron to the lower shell under emission of an X-ray photon - emitted energy corresponds to the energy difference of the shells - energy is well defined - K, L, M, N – shells are suitable to create X-rays - for too low energy of the primary photon, no ionisation is possible ad no X-rays are produced - optimum of characteristic radiation achieved slightly above the ionisation energy (interaction cross section)

emission lines of the characteristic spectrum

interactions - summary

other X-ray sources: synchrotrons Soleil (F)

other X-ray sources: synchrotrons particle accelerator, consisting of a LINAC, a „true“ synchrotron (Booster) and a storage ring electrons or positrons (depending on the source) are accellerated to relativistic velocities Linac: linear accellerator, where electrons reach high velocities in high frequency A. C. (20… 50 Me. V) „electron creation by an electron gun“ (Canadian Light source) after Ising and Wideroe

other X-ray sources: synchrotrons particle accelerator, consisting of a LINAC, a „true“ synchrotron (Booster) and a storage ring electrons or positrons (depending on the source) are accellerated to relativistic velocities Booster: true synchrotron accellerator, speeds particles up to several Ge. V track of the particles determined by magnetic fields: accelleration along straight sections through high frequency magnetic fields Canadian Light Source

other X-ray sources: synchrotrons particle accelerator, consisting of a LINAC, a „true“ synchrotron (Booster) and a storage ring electrons or positrons (depending on the source) are accellerated to relativistic velocities storage ring: particles are stored with the energy received in the booster ring The ‚ring‘ is actually a multigon: - at each ‚corner‘, the track direction of the particles is changed by bending magnets -> accelleration of particles - thus, at bending magnets, high energy X-ray photons are emitted, which can be used for experiments - straight sections are used for re-accelleration of the particles - X-radiations from ring sources has some special properties regarding coherence, energy distribution, divergence, intensity, …

other X-ray sources: synchrotrons comparison: beam energy + brilliance: undulator – bending magnets

other X-ray sources: synchrotrons the more photons of a specific wavelength and direction are concentrated at a certain point and time, the higher the brilliance is

Bringing synchrotron radiation to the experiment

Bringing synchrotron radiation to the experiment bending magnets: - simple, bent permanent magnets - radiation is emitted tangentially to the particle track (change in direction = accelleration) + large spectral range + low cost + simple process - no hard X-rays - low brilliance

Bringing synchrotron radiation to the experiment bending magnets: - simple, bent permanent magnets - radiation is emitted tangentially to the particle track (change in direction = accelleration) + large spectral range + low cost + simple process - no hard X-rays - low brilliance wiggler: - periodic array of permanent magnets - radiation is emitted in cones tangentially to the oscillatory motion of the particle beam - high elongation of particles = large spectral range + energy may be higher than in primary beam + high intensity via interference - expensive - requires cooling of magnets

Bringing synchrotron radiation to the experiment bending magnets: - simple, bent permanent magnets - radiation is emitted tangentially to the particle track (change in direction = accelleration) + large spectral range + low cost + simple process - no hard X-rays - low brilliance wiggler: undulator: + large spectral range + energy may be higher than in primary beam + high intensity via interference + minimal divergence + partially coherent + high brilliance - periodic array of permanent magnets - radiation is emitted in cones tangentially to the oscillatory motion of the particle beam - high elongation of particles = large spectral range - expensive - requires cooling of magnets - periodic array of permanent magnets - radiation of all cones is in interference condition - low oscillation amplitude creates a very localised, narrow beam - ‘low’ intensity - expensive

undulator equation ‚undulator parameter‘:

charakteristics of the 3 types of synchrotron radiation