4/2003 rev 2 i.4.11 – slide 1 of 21 session i.4.11 part i review of fundamentals module 4sources...
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4/2003 Rev 2 I.4.11 – slide 1 of 21
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)