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Session I.4.10

Part I Review of Fundamentals

Module 4 Sources of Radiation

Session 10 Linear Accelerators, Cyclotrons and Betatrons

IAEA Post Graduate Educational CourseRadiation Protection and Safety of Radiation Sources

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In this session we will discuss Charged Particles

We will discuss the acceleration of Charged Particles by:

Linear Accelerators Cyclotrons Betatrons

Overview

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Charged Particles

Useful for High Energy Research

Used directly in medical modalities (electron beam therapy)

Used to produce radionuclides employed in medical practices such as positron emitters for Positron Emission Tomography (PET)

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Charged Particles

A charged particle is any atomic particle with a positive or negative charge

A positive charge means the particle is a proton or positron or is an atom or molecule missing one or more electrons

A negative charge means the particle is an electron or beta particle

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Charged Particles

Charged particles are attracted to objects possessing an opposite charge (positive to negative and negative to positive)

Charged particles are repelled by objects with similar charge (positive vs positive and negative vs negative)

Attraction and repulsion are used to accelerate charged particles

+ -

+ +

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Basic Charged ParticleAccelerators

GLASSENVELOPE ELECTRON

STREAM

FILAMENT

CATHODE

FOCUSINGCUP

WINDOWUSEFUL X-RAYS

TUNGSTENTARGET

ANODE

This is an X-ray tube – it accelerates negatively charged electrons across a linear path, however, it is not considered a linear accelerator

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Other Charged ParticleAccelerators

Van der GraffGenerator

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Linear Accelerators

Once the particle has drifted through the first cavity, the polarity switches as seen in (b). The particle now is repelled by the first cavity and attracted by the second. After it drifts through the second cavity, the polarity again reverses so that the particle is repelled as it exits the second cavity (c).

All three images represent the same two cavities. The positively charged particle is attracted to the negatively charged first cavity in (a).

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Linear Accelerators

The drift tubes get longer as the particle’s velocity increases so that it spends the same amount of time in each tube.

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Electron Accelerators

Waveguides

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Linear Accelerators

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Electron Accelerators

6 MV short waveguide

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Electron Accelerators

18 MV long waveguide

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Electron Accelerators

Bending the electron beam

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Electron Accelerators

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Linear Accelerators

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Cyclotron

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Cyclotron

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+-+2

Cyclotron

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+ -+2

Cyclotron

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Cyclotron

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Cyclotron

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Betatron

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Betatron

target

x-ray beam

electron gun

donut

orbit

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Where to Get More Information

Cember, H., Johnson, T. E., Introduction to Health Physics, 4th Edition, McGraw-Hill, New York (2008)

Martin, A., Harbison, S. A., Beach, K., Cole, P., An Introduction to Radiation Protection, 6th Edition, Hodder Arnold, London (2012)

Firestone, R.B., Baglin, C.M., Frank-Chu, S.Y., Eds., Table of Isotopes (8th Edition, 1999 update), Wiley, New York (1999)