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Korea University Nanotube & Nanodevice Lab.. Korea University Nanotube & Nanodevice Lab.  What is X-ray?  Why do people study X-ray?  How to generate.

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Presentation on theme: "Korea University Nanotube & Nanodevice Lab.. Korea University Nanotube & Nanodevice Lab.  What is X-ray?  Why do people study X-ray?  How to generate."— Presentation transcript:

1 Korea University Nanotube & Nanodevice Lab.

2 Korea University Nanotube & Nanodevice Lab.  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 Korea University Nanotube & Nanodevice Lab.

4 Korea University Nanotube & Nanodevice Lab. Application in inspection FoodTire ArcheologyElectronics Medicine

5 Korea University Nanotube & Nanodevice Lab. What the Sun looked like in X-rays on April 27th, 2000 Materials spirals into the black hole or neutron star and heats up to very high temperature, it will give off X-rays. Application in astronomy

6 Korea University Nanotube & Nanodevice Lab. The electron collides with the atom, knocking an electron out of a lower orbital. The electron is attracted to the tungsten atom nucleus.

7 Korea University Nanotube & Nanodevice Lab. 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.

8 Korea University Nanotube & Nanodevice Lab. X-ray tube Microfocus X-ray Source (S mode) 0.8 (W mode)

9 Korea University Nanotube & Nanodevice Lab. https://w9.siemens.com/cms/oemproducts/Home/Products/Pages/X-rayTubes.aspx

10 Korea University Nanotube & Nanodevice Lab. 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

11 Korea University Nanotube & Nanodevice Lab.  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 Korea University Nanotube & Nanodevice Lab. Hot Cathode Cold Cathode Metal Field EmitterCNT Field Emitter Advantages- Small size Reduction of power consumption Small electron emission area - High aspect ratio Small radii Chemically stable Non-UHV Disadvantages Large size High power consumption Large electron emission area Chemically reaction with residual water and oxygen UHV for the stable operation - Cathode

13 Korea University Nanotube & Nanodevice Lab.  Emitter fabrication: Point emitter to get better FE performance Grow CNTs on a tip Adhere CNTs on a pin APL90(2007) JVSTB26(2008)702 Cathode

14 Korea University Nanotube & Nanodevice Lab. How to achieve smaller x-ray focal spot size? 1.Decrease the focus size of an electron beam. 2.Using a magnetic solenoid lens instead of electrostatic lens. 3.Thin transmission-type target is preferable to a thin reflection- type target. 4.Minimize the mechanical vibration: A sputter-ion vacuum pump was used. KAIST, Sung Oh Cho, APL90(2007) Result: x-ray focal spot size is less than 5 um. E-beam focusing

15 Korea University Nanotube & Nanodevice Lab. Result: resolution was higher than 700 nm. Electron beam diameter was 50 nm. Higher resolution Butler lens was designed with ELFIN software A 10M Ohm was used to stabilize emission current Transmission type. Mie University, Koichi Hata, JVSTB26(2008)702 E-beam focusing

16 Korea University Nanotube & Nanodevice Lab. E-beam focusing Details of electrostatic focusing unit Cross-sectional side view of exemplary components Patent - US Otto Zhou

17 Korea University Nanotube & Nanodevice Lab. 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: Reflection typeTransmission type Voltage: cathode to gate Voltage: cathode to anode Distance: cathode to gate Distance: cathode to anode Distance: cathode to target Field strength of lens Gate shape Target placed angleThickness of target E-beam focusing

18 Korea University Nanotube & Nanodevice Lab. 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 Korea University Nanotube & Nanodevice Lab. How much eV is needed? Power supply

20 Korea University Nanotube & Nanodevice Lab. Take copper for example: Power supply

21 Korea University Nanotube & Nanodevice Lab. 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… Power supply

22 Korea University Nanotube & Nanodevice Lab. Power supply

23 Korea University Nanotube & Nanodevice Lab. W ? Target

24 Korea University Nanotube & Nanodevice Lab. Reflection type targetTransmission type target Target The advantages of Transmission type target: X-ray emitting direction controllable Easy to obtain high magnification x- ray image

25 Korea University Nanotube & Nanodevice Lab. Target PaperAuthor Target type Target material APL78(2001)2578F. OkuyamaRCu APL81(2002)355O. ZhouRCu APL86(2005)123115Y. B. ZhangRCu APL86(2005)184104O. ZhouR- APL88(2006)103105S. P. LauaRCu APL88(2006) P. R. Schwoebel RMo APL89(2006)064106O. Zhou-Mo APL89(2006)103111O. ZhouRMo APL90(2007)183109Sung Oh ChoTW APPA115(2009)1078J. U. KimR- INS56(2009)1297Uk KimR Mo embedded Cu JVSTB23(2005)814H. BustaRCu JVSTB24(2006)950Y. SaitoRCu JVSTB26(2008)702Koichi HataTW JVSTB26(2008)706 Marjorie Munson R- RSI75(2004)1366F. OkuyamaaRCu RSI75(2004)3264O. ZhouRMo RSI76(2005)094301O. ZhouRMo Material Melting point(˚C) Boiling point(˚C) Thermal conductivity( W/m·K) Cu Mo W

26 Korea University Nanotube & Nanodevice Lab. 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 X-ray filter

27 Korea University Nanotube & Nanodevice Lab. Photographic filmSilicon diode Pic from google.com Pic from moxtek.com X-ray detector

28 Korea University Nanotube & Nanodevice Lab. 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 a void discharging to earth or arcing. Cooling

29 Korea University Nanotube & Nanodevice Lab. X-ray tube packaging Metal/Ceramic Tubes V.S. Glass Tubes 1.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 2.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. 3.Higher Heat Capacity

30 Korea University Nanotube & Nanodevice Lab.  X-ray focal spot size: European Standard EN : 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 Result analysis The size of X-ray focal spot, detector pixel pitch

31 Korea University Nanotube & Nanodevice Lab. Damage from high voltage 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. Pic from  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 Pic from Google Protection

32 Korea University Nanotube & Nanodevice Lab. Thanks for your attention !!


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