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Session I.4.11

Part I Review of Fundamentals

Module 4 Sources of Radiation

Session 11 X-Ray Production

IAEA Post Graduate Educational CourseRadiation Protection and Safety of Radiation Sources

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Overview

In this session we will discuss how X-rays are produced

We will also discuss some of the characteristics of low energy X-ray machines

Finally, we will discuss X-ray production from linear accelerators and other machines

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X-rays are useful for seeing what is inside something

Observation

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As was discussed in Session I.2.3, X-rays are produced either as

characteristic X-rays (electron transition from one energy orbit around the atom to another orbit more tightly bound to the nucleus) or

bremsstrahlung (electrons losing energy as they pass in the vicinity of atoms and are deflected by the positive and negative charges)

X-Rays

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characteristic X-rays have defined predictable energies (the energy difference between the two orbits traversed by the electron)

bremsstrahlung is composed of a spectrum of energies ranging from near zero to a maximum energy equal to the initial energy of the electron. The energy of the X-ray produced depends on how much energy the electron loses during an interaction (the most it can lose is all the energy it has – the least it can lose is a very small amount, almost zero)

X-Rays

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characteristic X-rays are useful for identifying things

since the energies emitted are “characteristic” of the atoms that make up the object, an analysis of the energies emitted can help to identify the object

thus characteristic X-rays are used for trace element analysis, which is important in forensic science (matching evidence samples) and other activities (such as identifying contaminants)

X-Rays

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bremsstrahlung X-rays are extensively used in medical and industrial applications

Medical X-ray units are used for Diagnostic Radiology and Linear Accelerators are used for Radiation Therapy

Industrial X-ray units are used to “diagnose” problems with inanimate objects (such as faulty welds on pipes) or to search for contraband (baggage inspection units at airports)

X-Rays

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Medical

Diagnostic(portable)

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Diagnostic Medical X-Ray Unit

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Diagnostic Medical X-Ray Unit

HIGH VOLTAGECABLES

X-RAY TUBE HOUSING (ASSEMBLY)

COLLIMATOR

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Medical

Dental(diagnostic)

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Superficial Therapy (low energy)

Medical

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Radiotherapy(high energy)

Accelerates electrons but can also produce high energy X-rays by directing the electron beam into a target as is done in a typical diagnostic X-ray unit.

Medical

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GLASSENVELOPE ELECTRON

STREAM

FILAMENT

CATHODE

FOCUSINGCUP

WINDOWUSEFUL X-RAYS

TUNGSTENTARGET

ANODE

X-Ray Unit

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Megavoltage X-ray LINAC

target

electrons

x-rays

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X-rays produced from high energy electrons impinging on a target tend to be scattered in the forward direction

X-rays produced by lower energy electrons tend to be scattered at right angles to the direction of the electron beam

X-Ray Emission

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Industrial

X-Ray Diffraction

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Industrial

Radiography

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For comparison, the output of a 1 TBq 192Ir Radiography Source is about 130 mGy/hr @ 1 m

Industrial

Some typical radiation output measurements from industrial radiography units with beryllium windows

X-Ray Unit kVp mA mGy hr-1 @ 1 mMagnaflux 150 10 36Sperry 275 10 66

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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)

Turner, J. E., Atoms, Radiation and Radiation Protection, 3rd Edition, Wiley VCH Verlag, Chichester (2007)

Dendy, P., P., Heaton, B., et al, Physics for Diagnostic Radiology, CRC Press, London (2011)