Accelerators and Applications- Summer Training in Physics 16

Accelerators and Its applications

Accelerators, Implantation, Applications-

Characterizations.

K. KamalakkannanResearch Scholar, UGC-DAE- [email protected]

Materials Science center, Department of Nuclear Physics

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Introduction

Generally, Those who are using telescope- Astrophysicist. Those who are using Microscope- Biologist. Those who are using Accelerators and Detectors- Nuclear Physicist. Why we need Accelerators?

To study the structure of the nuclear system, High energies are needed.

Ex.: De-Broglie wavelength: = To see the structure in detail of an object with linear dimension (d), we must use a wavelength comparable to or smaller than d. dThen, P, clearly, to see the details of very smaller objects like nuclear particles, High momenta & thus high energies needed. Ex. For d= 1 fm, We need about 20 MeV.


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Accelerators

An accelerator is a device that accelerate charged particles to high speed and to contain them in well defined beams.

Acceletarors

Acceleration by time varying

electric field

Cyclic Accelerator

Cyclotron

Synchrotron

MicrotronLinear Accelerator

Acceleration by constant

electric fieldLinear Accelerator DC Accelerator


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Particle Accelerator

Lorentz Force experienced by a particle with charge q moving in electric and magnetic fields.

= q[ + X ]

From work-energy theorem, the energy gained by the particle is equal to the amount of work done by the field on the particle: W= . = q X ). = q . + q. = q . W= q . = dt


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Particle AcceleratorSo, for particle acceleration, and therefore energy gain:• Magnetic fields cannot be used to change the kinetic energy of particles.• We have to use electric fields to accelerate particles for energy gain.• Acceleration occurs in the direction of the electric field.

In Particle Accelerators:• Longitudinal electric fields (i.e. electric fields along the direction of the particle motion) are required for accelerating particles.• Magnetic fields are used for bending the charged particle beams and for guidance and focusing.


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Particle Accelerator


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DC Accelerator These accelerators use a static, DC, potential difference between two conductors to impart a

kinetic energyW= qV0

They Include,1. Cockcroft- Walton generators2. Van de Graf generators3. Tandems

Highest voltages achieved are ~ 25 MVDifficult to establish and maintain a static DC field of 20+ MV


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DC Accelerator


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RF Accelerators


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Van de Graff Accelerator


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Van de Graff Accelerator


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Why do we need accelerator?

Particle accelerators are like microscopes that help physicists probe in to the subatomic world. They have led to the discovery of the fundamental building blocks of matter.

Understanding the structure and dynamics of materials and their properties (physics, chemistry, biology, medicine)

Sterilization Medical treatment of tumours and cancers Ion Implantation to modify the surface of materials. There is active, ongoing work to utilize particle accelerators for

Transmutation of nuclear wasteGenerating power more safely in subcritical nuclear reactors


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Why do we need accelerator?


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1. Ion Implantation

Ion implantation is a materials engineering process by which ions of a material are accelerated in an electrical field and impacted into a solid. This process is used to change the physical, chemical, or electrical properties of the solid.

Ion implantation equipment typically consists of an ion source, where ions of the desired element are produced, an accelerator, where the ions are electrostatically accelerated to a high energy, and a target chamber, where the ions impinge on a target, which is the material to be implanted.

Generally, what I am doing, - Doping the ions. Ex. B doping in SiC= p- SiC. Why implantation- Saturation limits, higher dose-

higher amount of charge carriers. Not possible in thermal diffusion.


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Flow Chart

N im

plantation

n- S

iC

Al or B

implantation

P- S

iC

i-layer Generation of Crystal Defects(Vacancies, Interstitials, IRDCs, Complexes)

Modification of the material properties (Ex. Crystallinity)

AnnealingRecrystallization, Defect reduction,

Recombination of the atoms andActivation of carriers

P-N and P-i-N devices


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2. Materials Characterization

Most Commonly used materials characterization techniques by using accelerators are,1. RBS,

2. Channeling3. ERDA4. PIXE5. NRA6. AMS


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2. Materials Characterization


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RBS

1911: Rutherford’s scattering experiments: 4He on Au Atomic nucleus, nature ⇒of the atom the ‘planetary model’.

Sir Ernest Rutherford


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Principle of RBS

Rutherford Backscattering (RBS) basically measures the number and energy of ions in a beam which back-scatter after colliding elastically with atoms in the near-surface region of a sample at which the beam has been targeted

Information:ThicknessCompositionConcentration Depth profileIncident Beam : HeEnergy :1 -3 Mev

Backscattered ions are measured using detector


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Basic concepts of RBS

Kinematic factor: It tells elastic energy transfer from a projectile to a target atom and can be calculated from collision kinematics (mass determination)

Scattering cross-section: It is the probability of the elastic collision between the projectile and target atoms (quantitative analysis of atomic composition)

Energy Loss: Energy loss of the projectile ions through the target (perception of depth)

These concepts allow RBS analysis to give quantitative depth distribution of targets with different masses


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