Lecture 3-Various Type of High Energy Sources for NDE Applications

7/22/2019 Lecture 3-Various Type of High Energy Sources for NDE Applications

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Radiography using X-Ray energies of 1MeV and above is commonly

considered as high energy radiography

The basic principle is similar to those of conventional radiography.

The placement of the source, object and film are similar to those in

conventional radiography.

Standard X-Ray films with lead or other intensifying screens are used

to produce radiographs.

The use of image quality indicators and identification markers are

also similar to those used in conventional radiography.

The high energy radiography is characteristic of high energy X-Ray

and gamma sources which prove to be highly advantageous.

High Energy Radiography


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Advantage

High energy for higher penetration(thick wall components)

Small focal spot for High sensitivity radiographs

Higher output for exposure time economy

Effective field size

Flatness of the radiation field

High Quality radiographs Use of slow films , Higher SFD ,

Small focal spot size

High latitude radiography

Cycle time reduction High Productivity


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Application

Radiography of thick wall weldments in Boilercomponents like Drums, Headers,Pipes etc.

Radiography of Heavy Wall Steel castings for High

Pressure Valves , Turbine casings etc.

Radiography of Rocket motors

Radiography of Oil field equipments for Petro-chemical

applications

Radiography of Engines for Aerospace applications


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High-energy Radiographic sources

High-energy machines

Co -60 Isotopic camera

Linear Accelerator

Betatron

Cyclotron

Van de Graaff generator


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6

Linac

Linacs are single pass accelerators for electrons,

protons, or heavy ions Thus the KE of the beam is limited by length of the

accelerator

4-25 MeV 0.5-1.5 m

50 GeV 3.2 km

250 GeV - 11 km

Linac static field, induction (time varying B field),

RF Operate in the microwave region

Typical RF for medical linacs ~ 2.8 GHz

Typical accelerating gradients are 1 MV/m 100 MV/m


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Used in

Nuclear reactions

X-ray sources in medicine

Possible solar flare mechanism

New

e- acceleration with EM induction

Before: fast e- - only in cosmic rays

CR sourc e Energy

Supernova 1014eV

Sun 105 eV

Milky Way 108eV

Betatron 108eV

Donald Kerst; e-

accelerator; 1940

Particle accelerator that uses the electric field

induced by a varying magnetic field to accelerate

electrons to high speeds in a circular orbit.

History


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Linear Accelerator Capable of generating X-Ray energies from 1-20 MeV .

RF LINAC uses microwave energy to create electric fields which are then

used to accelerate electrons to the speed of light . The accelerated electrons strike a metal target to produce X-Rays of

High Output and High Energy.

The RF power required - of the order of megawatts.

By very short pulses typically 5-10s.

The pulse RF energy 3-10 GHz is developed in special microwave RFgenerator tubes.

The microwave tubes require high voltage pulses and hundreds of ampsof current to operate.

The pulses to operate the microwave generators are created in a devicecalled Modulator.

The Modulator requires High Voltage DC that is produced in a HighVoltage supplier.


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Linear Accelerator

Schematic Diagram of RF Linac


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Functional sub-systems of Linac

Main sub systems Linac Tube

Modulator

Microwave system

Control Console

X-Ray Head Auxiliary Systems

Water Cooling System

Automatic Frequency Control

Dosimetry


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Linac Tube

Accelerates electrons - high energy electron beam when stopped by

a tungsten pellet generates the X rays. Microwave energy to create electric fields to accelerate the electrons.

RF power to set up these electric fields -typically Megawatts, the

power can be produced only in short pulses, typically 5 to 10

microseconds. The pulsed RF energy is developed in special microwave tubes -a

magnetron with output of 2.6 MW peak power.

Electron gun in Linac generates the electrons.

These electrons pass through a series of resonant structures calledcavities.


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Standing wave type of linac structure.

These cavities accelerate the electrons , which finally strike

the tungsten target.

In the target the electrons are converted into X rays.

Type of target called transmission target.

Electrons enter from one side and X rays exit from the

other.

The conversion efficiency of electrons to X rays - 15 %

Rest 85 % is converted into heat.

The target is water cooled to remove the heat.

Linac Tube


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Accelerator Structure

Microwave power (produced in the klyston) is transported to theaccelerator stricture in which corrugations are used to slow up thewaves synchronous with the flowing electrons.

After the flowing electrons leave the accelerator structure, they aredirected toward the target (for photon production) .

Amplification that occurs in the accelerator structure is in the closedended, precision crafted copper cavities where the electrical powerprovides momentum to the low-level electron stream mixed with themicrowaves.

Alternating positive and negative electric charge accelerates the

electrons toward the target, the negative voltage repels electronswhile the positive voltage attracts then, thereby pushing and pullingthe electrons along.

Charged particles experience the equivalent of a small voltagemultiple times, ending up with a large amount of kinetic energy


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Accelerator Structure

Length varies depending on the beam energy of the linac, as morecavities are used, higher energy is derived

Traveling wave: an electromagnetic wave travels to the right alongwith the electron, the electron is continuously accelerated as itmoves

Limitation: the electron and the electric field must move at the same velocity Irises: washer shaped metal discs that provide resistance to the travel of the

electromagnetic waves. As the electron increases in energy and velocity, the need for irises is reduced, so

irises are increasingly far apart and have increasingly wider openings.

Standing wave: microwave power is joined into the structure by

side-coupling cavities, rather than through the beam aperture,provides a shorter accelerating tube Makes use of the concept if interference

More efficient, more costly


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Linac Tube


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Modulator Provides high voltage pulses to magnetron.

In line type modulator- two parts: the charging cycle and the discharging

cycle.

Charging cycle - the charging inductor and the capacitance of the Pulse

forming network ( PFN) form a resonant circuit.

This resonance causes the pulse forming network to charge-up to twice

the voltage supplied by the high voltage supply. The charging diode keeps the PFN voltage at full voltage until the

discharge cycle is initiated.

The discharge cycle - initiated by conduction of power switch

(Thyratron). The discharge cycle results in a pulse of 12 kV ( with a pulse width

determined by the design of PFN).

With a typical ratio of 1:4 for the pulse transformer, the output pulse will

be around 48 kV pulse which is used to drive the magnetron.


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Modulator


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Micro wave system Two types - magnetron or a klystron in a NDT linac.

The choice of the RF generator is based on design requirements.

The output of the magnetron is fed into a device called a circulator.

3 port circulator - Buffer the magnetron from the accelerating linac tube

Highly dynamic load

At the beginning of the pulse, the accelerating structure is basically a

short circuit; most of the power is reflected back towards the source.

Magnetrons to a large extent are adversely affected by this reflected

power.

With the circulator in between, the reflected power is diverted into the

RF loads , in which it is absorbed. All the microwave power generated by the magnetron is transmitted

through waveguides with rectangular cross section.

The waveguides are filled with Sulpher Hexa Fluoride gas to withstand

the high electric fields at these power levels.


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Klystron

Klystron:A linear beam microwave amplifierrequiring an external oscillator or radiofrequency(RF) source driver

A form of radiowave amplifier, multiplies the amountof introduced radiowaves greatly.

Electron tube that is used to provide microwave powerto accelerate electrons

Microwave frequencies needed for linear acceleratoroperation are about three billion cycles per second


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Magnetron

Magnetron:device that provides high-frequency

microwave power that is used to accelerate the electrons

in the accelerating waveguide.

Electrons are emitted from the cathode and spiral in theperpendicular magnetic field. The interaction of the

spiraling electrons with the cavities in the anode creates

the high-frequency EM waves.

oscillator and amplifier used in low-energy


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X-Ray Head

Houses the Linac tube, microwave system, pulse transformer,

radiation shields, primary collimator, laser system etc.

Kept in the radiation hall and is mounted on a yoke and crane

arrangement.

X rays generated from the Linac tube is collimated by the primary

collimator having a full cone angle of 22.5 degrees

Lead radiation shields help in containing the radiation leakage levels

within 0.1 % of the forward intensity - mandatory requirement

Online type laser system generates a cross wire on the job to be

radio graphed This helps accurate positioning of the Linac with

respect to the component to be tested

The SF6gas panel is also located in the X ray head

The total weight of the X ray head -1800 kgs


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X-Ray Head

Control Console


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Provides a central location for monitoring and controlling thelinac

Take the form of a digital display, push button panel or videodisplay terminal (VDT)

All interlocks must be satisfied for the machine to allow the beamto be started

Provides a digital display for prescribe dose (monitor units),mechanical beam parameters such as collimator setting or gantryangle

The console also monitors the important parameters of the Linacsystem

Any fault which occurs in the system is readily seen on thecomputer screen

This console also has the facility to store the job details and theprint out of the job details on any particular day can be taken out

The machine has different stages of operation like STANDBY,READY, BEAMON etc.

Control Console


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Control Room


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Control Room


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Control Console


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Control Console

W C li S


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Circulates de-ionised water through critical components

like linac tube, magnetron, circulator, RF load target etc.

The temperature of the water is maintained around 30 deg

by the circulation of the chilled water through an heat

exchanger. Flow switches are provided in the Xray head to monitor the

flow.

Any fault in water flow will be reflected on the console and

the machine will stop.

l


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The accelerating structure operates at a very narrow

range of frequencies.

It is vital that the magnetron operates at the right

frequency.

As the accelerating structure heats up, the operating

frequency shifts, requiring the magnetron to track the

change so as to maintain maximum output.

The AFC circuit takes care of this shift in thefrequency.


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Flattening Filter

Flattening filter: (lead, steel, copper etc.) Modifies the narrow, non-uniform photon beam at the isocenter into a

clinically useful beam through a combination of attenuation of the center ofthe beam and scatter into the periphery of the beam

Measured in percent at a particular depth in a phantom (10 cm)

Must be carefully positioned in the beam or the beam hitting the patient willbe non-uniform, resulting in hot and cold spots

Flatness: a wide beam that is nearly uniform in intensity from oneside to the other (+/- 6%)

Symmetry: the measure of intensity difference between its opposite

sides (+/- 4%) Causes include the use of a wedge, misalignment of the flattening filter, andmisdirection of the electron beam before hitting the target.


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Linac HallSafety Features

Hoot & Buzzer

Zone monitor

Safety Interlock at the

Entrance of Linac Hall

Warning Lamps

6 MeV Linacs Comparison of specs


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6 MeV Linacs - Comparison of specs

Specifications Varian(USA) Siemens(USA) IRVIN(Italy) L & WResearch Inc.

(USA)

BARC/ ECIL

Energy (MeV) 6 6 5 6 6Steel penetration (mm) 200 200 180 200 200Dose rate

(Gy/min/m) 8 9 5 10 8Focal Spot Size (mm) 2 2 2 2 2Collimation Angle

(degree) 22 - 28 30 30Leakage radiation (at l m

distance

from radiation head)1% - 3% 0.1% 1%

Linac Frequency (MHz) 2856 2998 2998 2998 2856Control System PLC based - GESPAC logic

based PAC based PLC based

R di h f B il D


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Radiography of Boiler Drum


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Radiography of Space components


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Betatron, a type of particle accelerator that uses the

electric field induced by a varying magnetic field to

accelerate electrons(Beta particles) to high speeds in a

circular orbit.

The first successful Betatron was completed in 1940 at the

University of Illinois at Urbana-Champaign, under thedirection of the American physicist Donale. W .Kerst, who

had deduced the detailed principles that govern the

operation of such a device.

Modern compact Betatron designs are used to produce

high-energy X-Ray beams for a variety of applications

Maximum Capacity -300 MeV

Betatron

B


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Main Parts

A pulsed magnet circuit to accelerate electrons by

inductive fields.

An air gap to force magnetic field into the beam

transport region; electrons follow circular orbits in

the bending field.

Shaped magnetic fields for beam focusing.

Betatron

Principle of Betatron


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Principle of Betatron

Schematic diagram of a Betatron with Air gap


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Like the linear induction accelerator, the Betatron is the

circuit equivalent of a step-up transformer.

The main difference from the linear induction accelerator -

Magnetic bending and focusing fields are added to confine

electrons to circular orbits around the isolation core. The Betatron consists of an evacuated tube formed into a

circular loop and embedded in an electromagnet in which

the windings are parallel to the loop.

An alternating electric current in these windings produces

a varying magnetic field that periodically reverses in

direction.

Betatron

Betatron


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During one quarter of the AC cycle, the direction & strength

of the magnetic field & the rate of change of the field insidethe orbit, have values appropriate for accelerating

electrons in one direction.

Electron acceleration is controlled by two forces, one acting

in the direction of the motion of the electrons and the

other at right angles to that direction.

The force in the direction of electron motion is exerted by

the electric field produced via induction by thestrengthening of the magnetic field within the circle; this

force accelerates the electrons.

Betatron

Betatron


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The secondperpendicularforce arises as theelectrons move through the magnetic field, and itmaintains the electrons in a circular orbit within theclosed loop.

At the beginning of the appropriate quarter-cycle,electrons are injected into the Betatron, where theymake hundreds of thousands of orbits, gaining energy

all the while. At the end of the quarter-cycle, the electrons are

deflected onto a target to produce X-rays

Betatron

Parts of Betatron X-Ray system


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Parts of Betatron X Ray system

Detachable positioning Stand.

X-Ray window & integral dosimeterLaser alignment unit

Air circulation fans

X-Ray Accelerator(Radiator)



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Accelerator Chambers




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Power Unit



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Control Unit

Betatron


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2.5MeV Betatron 7.5MeV Betatron

Betatron

Betatron Applications


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Weld Inspection



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Inspection of Casting using 7.5 MeV Betatron




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Engine Block (Defect Inspection) Valve Housing (Functional Control)




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Inspection of Cargos

BRIDGE INSPECTION


Dual Energy Betatron


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gy

Dual energy Betatron

Different energies are selectable by changingthe acceleration cycle time.


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Comparison of particle accelerators

Instrument Shape Electricfield Magneticfield Electronenergy,

MeV

Van de Graaf

generator

linear constant constant 25

Linear

accelerator

linear variable constant 2.85

(50.000)

Cyclotron circle variable constant 0.025

Betatron torus constant variable 300

Synchrotron torus variable variable 10.000

Betatron in use (in the past)

1. Fast electrons in particle

physics

2. X-rays (radiation oncology)

Best e--accelerators now

1. Large electron-positron

collider 8*104MeV

2. International LinearCollider, 106MeV

h


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High EnergyIsotopic source

Electromagnetic radiation in the gamma ray region

Cobalt-60 (60-Mass number)

Cobalt-59 element by (n,Gamma) reaction.

Small pellets of Cobalt-59 are bombareded with

neutrons in a ractor.

27Co

59

(n,r)------ 27Co60

.

COBALT-60

C b l 60


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Cobalt 60

Activation cross-section for natural element: 37 barns.

1 barn-10-28M2

Energy: 1.17, 1.33 MeV gamma (1.25 MeV average).

Radiation output: 1.3 R/hr at 1 meter for 1Ci. (0.31

mGy/hr/GBq).

Thickness range: 50-200mm of steel.

Half-life: 5.3 years.

COBALT 60


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COBALT 60 C0-60 isotopes housed in shielded containers of High Z

Materials (Depleted Uranium)with a provision to take out

the source and project it to the desired location for RT

These devices are called Radiographic Cameras

Permissible leakage radiation levels outside the camera

shall be within the permissible levels as per internationalregulations (ICRP Regulations)

Isotopic sources are manipulated with the help of

mechanical teleflex driving devices and Guide tubes Sources are kept under lock and key when not under use

Co-60 isotopes are best suited for Radiographic testing

using Panoramic Technique.

Cobalt 60 Camera


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Cobalt 60 - 300 curie

Cobalt 60 Camera

Tech ops Spec 2T

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Lecture 3-Various Type of High Energy Sources for NDE Applications

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