X-ray source

1. X-ray source Yu-Ning Sun 2010.05.10

2. Outline • What is X-ray? • Why do people study X-ray? • How to generate X-ray? • Commercial product examples • The compositions of X-ray source • Cathode • Target • Power supply • E-beam focusing Etc.

3. What is X-ray?

4. Why X-ray? Application in inspection http://science.hq.nasa.gov/kids/imagers/ems/xrays.html Food Tire Medicine Electronics Archeology

5. Why X-ray? Application in astronomy Materials spirals into the black hole or neutron star and heats up to very high temperature, it will give off X-rays. What the Sun looked like in X-rays on April 27th, 2000 http://science.hq.nasa.gov/kids/imagers/ems/xrays.html

6. How to generate X-ray? The electron collides with the atom, knocking an electron out of a lower orbital. The electron is attracted to the tungsten atom nucleus.

7. Commercial products Detail detectability The highest amount of detail that can be shown in an image. Defined by the size of the smallest object that can be conveniently viewed, which, for nanofocus and microfocus X-ray tubes, is about half the size of the focal spot. http://www.phoenix-xray.com/en/products/x-ray_tubes/index.html

8. Commercial products X-ray tube Microfocus X-ray Source 0.25 (S mode) 0.8 (W mode) http://www.phoenix-xray.com/en/products/x-ray_tubes/index.html

9. Commercial products https://w9.siemens.com/cms/oemproducts/Home/Products/Pages/X-rayTubes.aspx

10. Commercial products XinRay Systems LLC is a joint venture of Siemens Medical Solutions and Xintek It uses Field Emission technology. Dr. Otto Zhou • The thermionic x-ray technology has several shortcomings: • High cathode operating temperature • Low temporal resolution • Limited programmability • Lack of multi-pixel capability http://www.xintek.com http://www.xinraysystems.com

11. The composition of X-ray source • Cathode: • CNT synthesis, emitter fabrication. • Electron beam focus and acceleration: lens, high power supply. • Target and others: • target material, type, filter, detector, cooling, vacuum packaging. • Result analysis: • focal spot size, resolution.

12. The composition of X-ray source Cathode

13. The composition of X-ray source Cathode • Emitter fabrication: • Point emitter to get better FE performance • Grow CNTs on a tip Adhere CNTs on a pin APL90(2007)183109 JVSTB26(2008)702

14. The composition of X-ray source E-beam focusing How to achieve smaller x-ray focal spot size? KAIST, Sung Oh Cho, APL90(2007)183109 Decrease the focus size of an electron beam. Using a magnetic solenoid lens instead of electrostatic lens. Thin transmission-type target is preferable to a thin reflection-type target. Minimize the mechanical vibration: A sputter-ion vacuum pump was used. Result: x-ray focal spot size is less than 5 um.

15. The composition of X-ray source E-beam focusing Higher resolution Mie University, Koichi Hata, JVSTB26(2008)702 • Butler lens was designed with ELFIN software • A 10M Ohm was used to stabilize emission current • Transmission type. Result: resolution was higher than 700 nm. Electron beam diameter was 50 nm.

16. The composition of X-ray source E-beam focusing Cross-sectional side view of exemplary components Details of electrostatic focusing unit Patent - US20080043920 Otto Zhou

17. The composition of X-ray source E-beam focusing It’s hard to calculate how the E-beam acts in the lens, so a software simulation should be helpful. Parameters we had to consider:

18. The composition of X-ray source X-ray focusing Why focus X-rays? Clearer and shaper image Better measurement The most commonly used reflecting materials for X-ray mirrors are gold (used in the Suzaku, XMM, and Swift satellites) and iridium (used by the Chandra X-ray Observatory). For gold, the critical reflection angle at 1 keV is 3.72 degrees

19. The composition of X-ray source Power supply How much eV is needed?

20. The composition of X-ray source Power supply Take copper for example:

21. The composition of X-ray source Power supply Matsusada Precision is a world leader high voltage power supply manufacturer. Since their establishment in 1972 as a general power supply manufacturer, Matsusada Precision has been designing, developing, manufacturing and marketing a wide range… http://www.matsusada.com/high-voltage/power-supplies.html

22. The composition of X-ray source Power supply http://www.spellmanhv.com/Products/X-Ray-Supplies.aspx

23. The composition of X-ray source Target W ?

24. The composition of X-ray source Target Reflection type target Transmission type target • The advantages of Transmission type target: • X-ray emitting direction controllable • Easy to obtain high magnification x-ray image

25. The composition of X-ray source Target

26. The composition of X-ray source X-ray filter An X-ray filter is a device to block or filter out some or all wavelengths in the X-ray spectrum. Results Using a Mo X-Ray generator: Zirconium - Absorbs Bremsstrahlung & K-Beta.Iron - Absorbs the entire spectra.Molybdenum - Absorbs Bremsstrahlung - Leaving K-Beta & K-Alpha.Aluminium - 'Pinches' Bremsstrahlung* & Removes 3rd Generation peaks.Silver - Same as Aluminium, But to greater extent.Indium - Same as Iron, But to lesser extent.Copper - Same as Aluminium, Leaving only 1st Generation Peak http://en.wikipedia.org/wiki/X-ray_filter

27. The composition of X-ray source X-ray detector Photographic film Silicon diode Pic from google.com Pic from moxtek.com

28. The composition of X-ray source Cooling The fraction of the total power emitted as X-rays is: W[%] = 100 · C · Z · U C =10-9 V-1. Z is the atomic number. e. g. Tungsten(Z=74) target at 100 kV has an efficiency of 0.74%. Most of the energy is converted to heat. High purity deionized water should be used in order to avoid discharging to earth or arcing.

29. The composition of X-ray source X-ray tube packaging • Metal/Ceramic Tubes V.S. Glass Tubes • Reduction of off-focus radiation • Problem: • Some electrons may be scattered backwards from the anode, colliding with the target again • Some of these electrons end up colliding with the target outside of the focal spot • In metal tubes, as the grounded metal casing attracts the scattered electrons away from the anode • Longer tube life expectancy • Problem: • In glass tube, target vaporized → deposited upon the glass → current flow → arcing • This is not a problem in metal tubes, as the metal enclosure is grounded to earth. • Higher Heat Capacity

30. The composition of X-ray source Result analysis • X-ray focal spot size: • European Standard EN 12543-5: Measurement of the effective focal spot size of mini and micro focus X-ray tubes. • NIMPRA591(2008)54 - Comparison of different methods for determining the size of a focal spot of microfocus X-ray tubes. • Resolution The size of X-ray focal spot, detector pixel pitch

31. The composition of X-ray source Protection Even X-rays of low energy penetrate soft tissue and cause cell damage. To be safe, one should ALWAYS stay away from a vacuum tube powered with more than a few kilovolts. • When working with relatively soft X-rays (U < 70 kV), a 20 cm (8 ") layer of concrete, sandstone, or brick is usually sufficient to reduce the radiation to a tolerable level, at least for short-term exposure. Damage from high voltage Pic from http://www.celnav.de/index.htm • Beyond 100 kV, one has to put at least two stone walls (20 cm each) between oneself and the tube to reduce radiation to a tolerable level. • Getting the habit of wearing a lead apron. Lead apron Picfrom Google

32. Thanks for your attention !!