X-ray source

Korea University Nanotube & Nanodevice Lab.

Nanotube & Nan-odevice Lab.

X-ray source

Yu-Ning Sun2010.05.10


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.


What is X-ray?


Why X-ray?

http://science.hq.nasa.gov/kids/imagers/ems/xrays.html

Application in inspection

Food Tire

ArcheologyElectronicsMedicine


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


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.


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.



Commercial products

X-ray tube

Microfocus X-ray Source


0.25 (S mode)0.8 (W mode)



Commercial products

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


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


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



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


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

CathodeThe composition of X-ray source


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


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


E-beam focusing


Details of electrostatic focusing unit

Cross-sectional side view of exemplary components

Patent - US20080043920 Otto Zhou


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



X-ray focusingThe 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


How much eV is needed?

The composition of X-ray sourcePower supply


Take copper for example:


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…




http://www.spellmanhv.com/Products/X-Ray-Supplies.aspx

http://www.spellmanhv.com/Products/X-Ray-Supplies.aspx


W ?

The composition of X-ray sourceTarget


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



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


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


Photographic film Silicon diode

Pic from google.com Pic from moxtek.com

The composition of X-ray sourceX-ray detector


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


X-ray tube packagingThe 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


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 analysisThe composition of X-ray source

The size of X-ray focal spot, detector pixel pitch


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

ProtectionThe composition of X-ray source


Thanks for your attention !!

X-ray source

Documents

thermionic xray technology

microfocus xray tubes

smaller xray focal spot

electron beam

focus size

commercial products

high cathode

field emission technology