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Basic Nuclear Physics - 2

Excitation, Ionisation, X-ray production and Auger electrons

Day 1- Lecture 2

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• To discuss the excitation and ionisation which are processes by which electrons are removed from their stable location

• To learn about accelerated charged particles, x-rays, Bremsstrahlung, Characteristic X-rays and Auger electrons

Objective

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• Binding Energy

• Excitation and Ionisation

• Accelerated charged particles and x-rays

• X- ray units

• Bremsstrahlung

• Characteristic Radiation

• Auger electrons

Contents

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Electron Shells

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2n2

Shell nMaximum No. of Electrons

K 1 2

L 2 8

M 3 18

N 4 32

O 5 50

P 6 72

Electron Shells

K

LMNO

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Shell Hydrogen Tungsten

K -13.5 -69,500

L -3.4 -11,280

M -1.5 -2,810

N -0.9 -588

O -0.54 -73

Binding Energy

(Binding Energy in eV)

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Binding Energy

10

30

40

50

60

70

100

80

90

110

20

50 60 70 80 90 10010 20 30 400

0

Atomic Number (Z)

Bin

ding

Ene

rgy

(keV

)

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Excitation

electronorbitals

excited state

ground state

energy

nucleus

atom

energy

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normal energy level

higher energy level

excitedelectron

energy

Excitation

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nucleus

electron

energy

excited state

Excitation

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Excitation

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Ionisation

Ionisation of an outer shell electron

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Ionisation

Ionisation of a K-shell electron

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Accelerated Particles

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W

e-

Tungstennucleus X-ray

Bremsstrahlung

In one process radiation is emitted by the high-speed electrons themselves as they are slowed or even stopped in passing near the positively charged nuclei of the anode material. This radiation is often called Brehmsstrahlung [Ger.,=braking radiation].

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Bremsstrahlung

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GLASSENVELOPE ELECTRON

STREAM

FILAMENT

CATHODE

FOCUSINGCUP

WINDOWUSEFUL X-RAYS

TUNGSTENTARGET

ANODE

X-Ray Unit

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Diagnostic Medical X-Ray Unit

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Characteristic Radiation

incidentelectron vacancy

createdelectron

transitionx-ray

emitted

In a second process radiation is emitted by the electrons of the anode atoms when incoming electrons from the cathode knock electrons near the nuclei out of orbit and they are replaced by other electrons from outer orbits

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Characteristic Radiation

Opticalradiation

unexcitedatom

N

M

L

K radiation

L radiation

Opticalorbits

Valenceelectron

K

M radiation

70,000

11,000

2500

0

En

erg

y(

6v)

no

tto

sca

le

L radiation

W

Optical energy levels

K

L

O

M

N

K radiation w

M

N

L

K

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Polyenergetic vsMonoenergetic X-Rays

Energy

Polyenergetic

E1 E6 E7 E8 E9 E10 E11 E12 E13 E14E2 E3 E4 E5 Emax

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missingdue to

filtration

Energy

Polyenergetic

E1 E6 E7 E8 E9 E10 E11 E12 E13 E14E2 E3 E4 E5

Polyenergetic vsMonoenergetic X-Rays

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Polyenergetic

E1 E6 E7 E8 E9 E10 E11 E12 E13 E14E2 E3 E4 E5

Monoenergetic

Eeff

Polyenergetic vsMonoenergetic X-Rays

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Characteristic Radiation

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Characteristic Radiation

Opticalradiation

unexcitedatom

N

M

L

K radiation

L radiation

Opticalorbits

Valenceelectron

K

M radiation

70,000

11,000

2500

0

En

erg

y(

6v)

no

tto

sca

le

L radiation

W

Optical energy levels

K

L

O

M

N

K radiation w

M

N

L

K

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Auger Electrons

Auger electrons are a special case of Internal Conversion.

During the Internal Conversion Process, a gamma photon from the nucleus interacts with and transfers all of its energy to a tightly bound (K-shell) orbital electron.

The electron is ejected from the atom with considerable energy, equal to that of the initial gamma photon minus the binding energy.

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Auger Electrons

characteristic x-ray Auger electron

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Where to Get More Information

Cember, H., Johnson, T. E, Introduction to Health Physics, 4th Edition, McGraw-Hill, New York (2009)

International Atomic Energy Agency, Postgraduate Educational Course in Radiation Protection and the Safety of Radiation Sources (PGEC), Training Course Series 18, IAEA, Vienna (2002)