INTERACTIONS OF IONIZING RADIATION WITH MATTERS

DR. CHAU VAN TAODEPARTMENT OF NUCLEAR PHYSICS

NATURALSCIENCES UNIVERSITY

Questions

What is radiation?

What is ‘ionizing’ radiation?

How do we measure radiation?

Where does radiation come from?

What are the effects of radiation?

Is radiation good for anything?

nucleusnucleus

proton

neutron

electronelectron

Atomic Structure and Radioactive DecayAtomic Structure and Radioactive Decay

Atomic StructureAtomic Structure

RöntgenRöntgen

18951895

Discovery Discovery of X-rayof X-ray

Pierre & Marie Pierre & Marie CurieCurie 18981898 Discovery ofDiscovery of Ra, Ra, PoPo

Becquerel Becquerel

18961896

SpontaneouSpontaneous s radioactivitradioactivityy

　　 Hahn Hahn

19381938

Discovery Discovery of fissionof fission

Discovery of Radiation Discovery of RadiationDiscovery of Radiation

Ernest Rutherford(1871-1935) Albert Einstein(1879- 1955)

Types of Radiation and Nuclear Energy

Atomic Structure and Radioactive DecayAtomic Structure and Radioactive Decay

Atoms and IsotopesAtoms and Isotopes

XN

A

Z

X: Chemical SymbolX: Chemical Symbol

AA: : Atomic mass numberAtomic mass number

ZZ: : Atomic numberAtomic number

N: Neutron numberN: Neutron number

or X-A

He4

2 He-4

A=Z+N4 2 2

electronelectron

Atomic Structure and Radioactive DecayAtomic Structure and Radioactive Decay

Co-60

Proton : 27Neutron: 33

Ni-60*

Proton : 28Neutron: 32

-decay and -decay and -ray emission-ray emission

Ni-60

Proton : 28Neutron: 32

electromagneticelectromagneticradiationradiation

More Radioactivity

+60Co Beta ray(electron)

++226Ra Alpha ray

(helium nucleus)

7BeGamma ray

+-electron

7Be 7Li +

11C 11B + +

60Co 60Ni + –

226Ra 222Rn +

+11C Positron

Antoine Henri Becquerel

(1852—1908)

Antoine Henri Becquerel

(1852—1908)

Discovered radioactivity of uranium

Discovered radioactivity of uranium

proton

neutron

Atomic Structure and Radioactive DecayAtomic Structure and Radioactive Decay

-decay-decay

U-238

Proton : 92Neutron: 146

Th-234

Proton : 90Neutron: 144

nucleusnucleus

-ray

Lead block

Radioactive substance

-ray

-ray

-ray

(+)

(-)

Electrically charged plates

Photographic plate

Types of RadiationTypes of RadiationTypes of RadiationTypes of Radiation

Types of RadiationTypes of Radiation

Types of radiation Charge

Mass

(amu)Remarks

-ray +2 4Very short range

Highly ionizing

-ray -1 0.0005 Short range

-ray 0 0 Long range

neutron 0 1 Long range

Types of RadiationTypes of Radiation

Half-life Time of RadionuclideHalf-life Time of Radionuclide

Characteristics of RadiationCharacteristics of Radiation

A = A0e-t

: Probability of disintegration per unit time

Half Life, Ｔ 1/2 = log2 /

Half-life Time of RadionuclideHalf-life Time of Radionuclide

Characteristics of RadiationCharacteristics of Radiation

Nuclide Half-life24Na 15.0 h

222Rn 3.8 d131I 8.0 d

60Co 5.3 y90Sr 28.8 y

137Cs 30 y226Ra 1600 y239Pu 24000 y238U 4.5x109 y

Characteristics of RadiationCharacteristics of Radiation

Penetrating DistancesPenetrating Distances

and X

neutron

Paper Plastic Lead ConcreteSkin Aluminum Iron Water

Electromagnetic Radiation

f = c/f = c/

Speed of lightBUT:

Radiation can also be interpreted as particles (photons) with energy E

E = hfE = hf

Planck’s constant

‘Ionizing’ Radiation

+

++

+

-

-

Radiation that is energetic enough to remove a tightly bound electron from a neutral atom

Radiation that is energetic enough to remove a tightly bound electron from a neutral atom

RadiationElectron

Ion

‘Ionizing’ Radiation

Different kinds of radiation produce different patterns of ionizationDifferent kinds of radiation produce different patterns of ionization

+++ + + +

+++ + + +

+++ + + +

+++ + + +

Electromagnetic Spectrum

IonizingNon ionizing

AA

Measuring Radiation (Ion Chamber)

Measuring Radiation (Geiger Counter)

Geiger–Müller Tube

Geiger–Müller Tube

Measuring Radiation (Scintillator)

1024…

4096… 410 = 1,048,576

ScintillatorScintillator Light guideLight guide

Photomultiplier tube

Photomultiplier tube

DynodesDynodes

Electrical pulse

Electrical pulse

1

4

16

64

256

PhotocathodePhotocathode

The Gamma Spectrometer

Lesson 1 - Inverse Square Law of Gamma Radiation

I0

x1

I1

I0

21

01 x

IkI

x2

I1I2

I0

2

1

x

mm mm

logk-2logx

oI/I

2o

x

IkI

oI/I

2o x

k

I

I xlog2klog]I/Ilog[ o

x x

Io

Lesson 2 –The Decrease Of Gamma Intensity

Interaction of Radiation with MatterInteraction of Radiation with Matter

Interaction ofInteraction of Electromagnetic RadiationElectromagnetic Radiation withwith Matter Matter

Photoelectric Effect

photoelectron

raye-

E:  energy of the incident photonEs:  energy of the scattered photonq :  the scattering anglem:  electron mass

Interaction of Radiation with MatterInteraction of Radiation with Matter

Interaction ofInteraction of Electromagnetic RadiationElectromagnetic Radiation withwith Matter Matter

Compton Scattering

ray

’ray

electron

e-

Pair Production

Interaction of Radiation with MatterInteraction of Radiation with Matter

E  =  2mc2 + E+ + E-

m:  electron rest massc:  the speed of lightE+:  kinetic energies of the positron E-:  kinetic energy of the electron

Interaction ofInteraction of Electromagnetic RadiationElectromagnetic Radiation withwith Matter Matter

positron

electron

raye-

e+

Interaction of Radiation with MatterInteraction of Radiation with Matter

Photoelectric Effect

Pair Production

Compton Scattering

µ

xo e.II

Ix

xe

mm mm

-x

oI/I

xo e.II

oI/I

xo eI/I x]I/Iln[ o

x x

electronelectron

Co-60

Proton : 27Neutron: 33

Ni-60*

Proton : 28Neutron: 32

Lesson 3 - The Gamma Spectrum

Ni-60

Proton : 28Neutron: 32

electromagneticelectromagneticradiationradiation

Lesson 3 - The Gamma Spectrum

Cobalt Spectrum

THANK YOU FOR ATTENTION