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Korea University Nanotube & Nanodevice Lab.
Nanotube & Nan-odevice Lab.
X-ray source
Yu-Ning Sun2010.05.10
Korea University Nanotube & Nanodevice Lab.
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.
Korea University Nanotube & Nanodevice Lab.
What is X-ray?
Korea University Nanotube & Nanodevice Lab.
Why X-ray?
http://science.hq.nasa.gov/kids/imagers/ems/xrays.html
Application in inspection
Food Tire
ArcheologyElectronicsMedicine
Korea University Nanotube & Nanodevice Lab.
Why X-ray?
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.
http://science.hq.nasa.gov/kids/imagers/ems/xrays.html
Application in astronomy
Korea University Nanotube & Nanodevice Lab.
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.
Korea University Nanotube & Nanodevice Lab.
Commercial products
http://www.phoenix-xray.com/en/products/x-ray_tubes/index.html
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.
Korea University Nanotube & Nanodevice Lab.
Commercial products
X-ray tube
Microfocus X-ray Source
http://www.phoenix-xray.com/en/products/x-ray_tubes/index.html
0.25 (S mode)0.8 (W mode)
Korea University Nanotube & Nanodevice Lab.
Commercial products
https://w9.siemens.com/cms/oemproducts/Home/Products/Pages/X-rayTubes.aspx
Korea University Nanotube & Nanodevice Lab.
Commercial products
XinRay Systems LLC is a joint venture of Siemens Medical Solutions and Xintek It uses Field Emission technology.
Dr. Otto Zhou
http://www.xintek.comhttp://www.xinraysystems.com
The thermionic x-ray technology has several shortcomings:
High cathode operating temperatureLow temporal resolutionLimited programmabilityLack of multi-pixel capability
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.
The composition of X-ray source
Korea University Nanotube & Nanodevice Lab.
The composition of X-ray source
Hot CathodeCold Cathode
Metal Field Emitter CNT 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 con-
sumption• Large electron
emission area• Chemically reac-
tion with residual water and oxygen
• UHV for the stable operation -
Cathode
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)183109 JVSTB26(2008)702
Cathode
The composition of X-ray source
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)183109
Result: x-ray focal spot size is less than 5 um.
The composition of X-ray sourceE-beam focusing
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
The composition of X-ray sourceE-beam focusing
Korea University Nanotube & Nanodevice Lab.
E-beam focusing
The composition of X-ray source
Details of electrostatic focusing unit
Cross-sectional side view of exemplary components
Patent - US20080043920 Otto Zhou
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 con-sider: Reflection type Transmission 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 angle Thickness of target
E-beam focusing
The composition of X-ray source
Korea University Nanotube & Nanodevice Lab.
X-ray focusing
The composition of X-ray source
Why focus X-rays?
Clearer and shaper imageBetter 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
Korea University Nanotube & Nanodevice Lab.
How much eV is needed?
The composition of X-ray sourcePower supply
Korea University Nanotube & Nanodevice Lab.
Take copper for example:
The composition of X-ray sourcePower supply
Korea University Nanotube & Nanodevice Lab.
http://www.matsusada.com/high-voltage/power-supplies.html
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…
The composition of X-ray sourcePower supply
Korea University Nanotube & Nanodevice Lab.
The composition of X-ray sourcePower supply
http://www.spellmanhv.com/Products/X-Ray-Supplies.aspx
Korea University Nanotube & Nanodevice Lab.
W ?
The composition of X-ray sourceTarget
Korea University Nanotube & Nanodevice Lab.
Reflection type target Transmission type target
The composition of X-ray sourceTarget
The advantages of Transmission type target:• X-ray emitting direction controllable• Easy to obtain high magnification
x-ray image
Korea University Nanotube & Nanodevice Lab.
The composition of X-ray sourceTarget
Paper Author Target type
Target material
APL78(2001)2578 F. Okuyama R Cu
APL81(2002)355 O. Zhou R Cu
APL86(2005)123115 Y. B. Zhang R Cu
APL86(2005)184104 O. Zhou R -
APL88(2006)103105 S. P. Laua R Cu
APL88(2006)113902 P. R. Schwoebel R Mo
APL89(2006)064106 O. Zhou - Mo
APL89(2006)103111 O. Zhou R Mo
APL90(2007)183109 Sung Oh Cho T W
APPA115(2009)1078 J. U. Kim R -
INS56(2009)1297 Uk Kim RMo
embedded Cu
JVSTB23(2005)814 H. Busta R Cu
JVSTB24(2006)950 Y. Saito R Cu
JVSTB26(2008)702 Koichi Hata T W
JVSTB26(2008)706 Marjorie Munson R -
RSI75(2004)1366 F. Okuyamaa R Cu
RSI75(2004)3264 O. Zhou R Mo
RSI76(2005)094301 O. Zhou R Mo
Material Melting point(˚C)
Boiling point(˚C)
Thermal conductivity(
W/m·K)
Cu 1085 2927 400
Mo 2623 4639 139
W 3422 5555 170
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.
http://en.wikipedia.org/wiki/X-ray_filter
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
The composition of X-ray sourceX-ray filter
Korea University Nanotube & Nanodevice Lab.
Photographic film Silicon diode
Pic from google.com Pic from moxtek.com
The composition of X-ray sourceX-ray detector
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 avoid discharging to earth or arcing.
The composition of X-ray sourceCooling
Korea University Nanotube & Nanodevice Lab.
X-ray tube packaging
The composition of X-ray source
Metal/Ceramic Tubes V.S. Glass Tubes
1. Reduction of off-focus radiationProblem:
• 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 anode2. Longer tube life expectancyProblem:
In glass tube, target vaporized → deposited upon the glass → current flow → arcingThis is not a problem in metal tubes, as the metal enclosure is grounded to earth.3. Higher Heat Capacity
Korea University Nanotube & Nanodevice Lab.
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
Result analysis
The composition of X-ray source
The size of X-ray focal spot, detector pixel pitch
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 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 Pic from Google
Protection
The composition of X-ray source
Korea University Nanotube & Nanodevice Lab.
Thanks for your attention !!