waqas ahmad report study of radiation detection and measurements 1

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Mid Sweden UniversityDepartment of Informationtechnology and media (ITM)

A Study of RadiationDetection and Measurement

2010-10-08

M.Sc. project reportElectrical Engineering

A Study of Radiation Detectionand Measurements

Waqas Ahmad



A Study of Radiation Detectionand MeasurementWaqas Ahmad

Abstract2010-10-088

Abstract´The purpose of this report is to understand the working andbasic principles of radiation detection and measurement. In thisreport we will study about radiation sources and theirinteractions with metals. Moreover a study about the detectorsthat can detect this interaction and the statistical formulas toconclude meaningful results from the detector measurementswill be conducted.

ii



A study of Radiation Detectionand MeasurementWaqas Ahmad

1 Introduction & OverallAim

2010-10-088

Introduction & Overall AimIn this report we will study five chapters from [1].

1. Radiation Sources

2. Radiation Interactions

3. Counting Statistics and Error Prediction

4. Radiation Spectroscopy with Scintillators5. Semiconductor Diodes





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Radiation SourcesAny material that goes under radioactive decay and producesradiations is called a radioactive source.Our concerned sources can be categorized like

1.1 Definition of terms and abbreviations

1.1.1 Radioactivity

The process of decaying radioactive/radioisotope source bysome fundamental rules. This decay of the radioactive element

Charged particleRadiation

Fast electronsHeavy charged

particles

Betadecay

Internalconversion

AugerElectrons

Alphadecay

Spontaneous fission

Uncharged particle Radiation

Electromagnetic Radiation

Neutrons

Gamma Rays FollowingNuclear Reactions

Bremsstrahlung

Characteristic X-Rays

Excitation by radioactivedecay

Excitation by externalradiation

SynchrotronRadiation

Spontaneous fission

Radioisotope (α, n)Sources

Photoneutron Sources

Reaction from Acceleratedcharged practical





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results in the emission of radiations and this is defined by thefollowing relation

Where λ is the decay constant and has a value = 3.7x1010

disintegration per second and N is the number of radioactivenuclei.

1.1.2 Specific Activity

Specific Activity is defined as activity per unit mass

Where,

M = Molar Weight

Av = Avogardo’s Number

λ = is the decay constant having value = 3.7x1010

1.1.3 Electron VoltEnergy is measured as electron volts and that can be definedas the energy of an electron that has been accelerated througha potential difference of one (1) volt, also

1 eV = 1.602 x 10-19 J

1.2 Radioactive Sources

1.2.1 Fast Electron Sources

A. Beta Decay

It is a radio isotope that decays by beta-minus emissionand is characterized by the following equation

Whereas X and Y are initial conditions v is anti neutrino.

B. Internal Conversion

Lower orbit Electrons are kick out due to the interactionwith the excited nuclear is called internal conversion





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C. Auger Electrons

When an electron fills the hole produced due to a leavingof a electron it transfer the energy to the nearby electronand kick it out that is call auger electron

1.2.2 Heavy charged practical sources

A. Alpha decay

Alpha decay is well defined by the following equation

This means that during an alpha decay two alphaparticles are emitted from a nucleus of an atom which

results in a decrease of 4 in the atomic mass and adecrease of 2 in the atomic number of that atom.

B. Spontaneous fission

Spontaneous fission is that process in which an unstableatom of any element disintegrates into two atoms of smaller elements which results in the emission of energetic heavily charged particles with a mass greaterthan alpha particles.

1.2.3 Sources of Electromagnetic Radiations

A. Gamma Rays Following Beta DecayWhen excited nuclei go to their lower nuclear level, itemits gamma rays. The excited state of the nuclei iscreated in the decay of parent radionuclide

B. Annihilation Radiations

During beta decay, some additional weakelectromagnetic radiations are produced that travel justfew millimetres (mm) and lose their kinetic energy. Justbefore losing their energy they are absorbed by electronsin the absorbent metal. This process is calledannihilation. This electron and its positron disappear to

produce two opposite directed photons and thisphenomenon is called annihilation of radiations.





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C. Gamma Rays Following Nuclear Reactions

When alpha particle hits a nucleus, it produces heaviernucleus that is in excited state then it goes to normalstate emitting energy equal to a gamma ray.

D. Bremstrahlung

When a fast electron interacts with matter, it produceselectromagnetic radiations and these radiations areknown as Bremstrahlung.

E. Characteristic X-Rays

When an electron is excited from its normal orbit tohigher orbit with an external force, it remains in thehigher orbit for a very short time after which it comesback to normal state releasing the characteristic X-rays.

The energy of X-rays is equal to the difference of twoenergy bands.

F. Synchronous Radiations

When a beam of electrons is forced to move in a circularorbit, during each cycle small fraction of energy is

radiated away from the circular path, this phenomenon isknown as synchronous radiation.

1.2.4 Neutron Sources

A. Spontaneous Fission

Most of transuranic have spontaneous fission decay andemit several neutrons for example 252CF is most commonspontaneous fission source for neutrons.

B. Radioisotope (α, n) Sources

When an alpha (α) particle is made to interact withsuitable materials it has ability to produce a neutron. Themaximum probability of getting a neutron when berylliumis targeted with alpha particles a neutron is produced inthis reaction.

C. Photoneutron Sources





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Neutron can be produced when gamma rays arecombined appropriate target metal that depends on the

energy of the gamma rays.





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Radiation InteractionsCharged partials can be divided in to two type

Light charged particles

Electrons, including positrons and beta particlesfrom radioactive decay, Auger electrons, andinternal conversion electrons

Heavy charged particles

Alpha particle, fission fragments, protons,deuterons, tritons, and mu and pi mesons.

1.3 Heavy charged particles interaction

There are three types of interaction

1.3.1 Soft collisionCoulomb-force interactions with the external nuclear field

1.3.2 Hard collision

1.3.3 Delta rays

Electron that is kicked with sufficient kinetic energy

1.3.4 Stopping power

• Liner stopping powerIt is the ratio of the energy loss of the partial to thecorresponding differential path length

dxde s −=

It is also called specific energy or rate of energy loss





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• Bethe formulaAs the velocity decreased S increases that is sated by the

bethe formula

NBvm

z

dx

de2

24e4

Ο

Π=−

1.4 Energy loss characteristic

1.4.1 The Bragg curve

Bragg curve is a plot of specific energy loss along thetrack of a charged particle

1.4.2 Energy Straggling

When mono energy beam pass through a martial the resultantbeam has many energies or band of energy this distribution of energy is measured as energy straggling

1.5 Particle range

Range is defined thickness that just leads to the energy of thepractical to zero

Mean range





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It is defined as the thickness of the absorber that just makesthe energy of the practical to half

Extrapolated rangeIt is defined as the thickness of the absorber that is

obtained by extrapolating the liner portion of the transmissioncover from half energy make the energy of the practical to half

1.5.1 Range straggling

Like energy straggling range also band due to energystraggling and it can be measure Range straggling

1.5.2 Stopping time

This time that a practical take to fully absorbed in theabsorber

1.6 Energy loss in thin absorbers

Energy loosed in the thin absorber can be defined as

( t dx

de E avg

−=∆





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t = thickness of the absorber

(dx

de− = S or stopping power





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Counting Statistics and Error PredictionCounting statistics

it is statistical analysis to fetch result from the randomproximity data of the radioactive reactions

Error prediction

Through this we fine the precision of the

result and accepted rang of the random error

Presentation of data

Data

Any set of measurement regarding to some specificmeasurement is called data

N x x x x ,...,,

321

Sum and experimental mean

Sum is the most basic presentation of the data. And it isdenoted by

∑ So

sum ∑ = ∑=

N

i

i x1

Experimental mean N

xe

∑≡

Frequency distribution





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It shows the average of the occurrences of the same result of same value of the data .it Is powerful way to define the data as

N

xvaluetheof soccurrenceof number x f ≡)(

Deviation

It the amount by wich the data differs from its mean value

x xii−≡ε

Variance

It tell how different a one group of entries form other in thegiven data

22 )( x x sx−=





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Radiation Spectroscopy withScintillators

Scintillators

Scintillators are the crystal material that are used to detectradiations as they glow after being exposed to radiations

Radiation SpectroscopyRadiation Spectroscopy is the study of distribution of energiesacross different energy bands of a particle emitted by nuclei.

Gamma Ray Interactions

Gamma ray can interact with matter in following threemanners.

a) Photonic Absorption

If gamma ray photon is totally absorbed in the atom, the

phenomenon is known as photonic absorption. This willkick out an electron from the atom called photoelectron. This photoelectron will release energy equal to thegamma ray when it will come back to its original shell

b) Compton Scattering

hv





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If gamma ray photon does not absorb fully and deflectsat some angle after the creation photon recoil electron,

the energy is divided between electron and gamma rayphoton that depends on the angle of scattering.

c) Pair ProductionWhen gamma ray photon interacts with a strongelectrical field, resulting in the produces electron andpositron pair and this phenomenon is known as pairproduction. As two 2mc2 is required to produce electronpositron pair so the minimum required energy is 1.02MeV.

Response of DetectorsSecondary Gamma RadiationsSecondary Gamma Radiations are those radiations that areproduced during the Compton scattering.

Mean Free Path The mean free path is defined as the average distance coveredby a gamma ray between two successive interactions with anymatter. Generally the mean free path for gamma ray is severalcentimeters (cm).We can categorize detectors according to their size as follows:

a) Small Detectors (less than 2cm)

In small detectors all the electrons and positronsproduced during pair production and secondary gammarays produced during scattering escape from the sensor.





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b) Very Large Detectors (around 10 cm)In case of very large detectors, nothing escapes from thesensor and all the energy is deposited on the sensor.





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c) Medium Detectors ()

Multiple scattered and annihilation photon escapes fromthe sensor and the rest of the energy is deposited in thesensor.

Methods in Gamma ray Spectrometers

Continuum Reduction





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Semiconductor DiodesSemiconductor diode detector

Detectors that use semiconductor as the basic principle for thedetection are called semiconductor diode detectors

Semiconductor terms

Conduction band The shell in wich electron have much energy that they can bekicked from the atom is called conduction band

Valance band The band that just comes after the conduction band is calledvalance band

Band gap The gape between conduction band and valance band is called

band gap

Electron hole pairWhen the electron is kicked from the bond it leaves a vacancy

that is called hole and that electron and that vacancy is calledelectron hole pair

Semiconductors are such material in wich band gape is enoughsmall that the atom can be excited to move in the conductionbands

The band gape is about 1ev





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Procedure to make semiconductor

Semicontors are made by adding some impurities in theinsulator that result some loss baond between them so that wecan remove electron from those loss bond to make electronhole pair to carry the current through the semiconductor

Dopants

The impurity that is added to make loss bond is called dopants

Silicon diode as radiation detector

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A Study of RadiationDetection and Measurements- Error: Reference source notfoundWaqas Ahmad 2010-10-08

References[1] http://www.med.harvard.edu/JPNM/physics/didactics/physics/charged/lect.html

[2] M. Eriksson, ”Dynamic Single FrequencyNetworks”, IEEE Journal on Selected Areas inCommunications (J-SAC), vol. 19, nr. 10, 2001, s. 1905-1914. (Example of reference to article in scientific

journal)

[3] S. Strömquist, Skrivboken. 4 uppl. Malmö:Gleerups., 2000 (Example on reference to book)

[4] L. Forsslund, ”Rapportering avforskningsresultat - ett rationaliseringsobjekt”. Industriellteknik , 22, 1969, s. 361-363. (Example of reference to amagazine article)

[5] N. Bie, “Minspel på Internet”. DagensNyheter 7 juli, 1997, sidan 5. (Example of reference to anarticle in a newspaper)

[6] K. Berg, ”Inledning till kunskap”, Fiktivahögskolan, rapport nr XYZ-102, 2003, 120 sidor.(Example of reference to other report)

[7] AB Benzlers. Växelboken. Kuggväxlar,kuggremmar, kilremmar etc. Mecman. Hydraulik, SKF.Huvudkatalog. (Example of reference to a catalogue)

[8] Microsoft Corporation, 1992: Microsoft Word Användarhandbok. Ordbehandlingsprogram för Macintosh Version 5.0. (Example of reference to aAppendix D: Result of questionnaire survey

http://www.med.harvard.edu/JPNM/physics/didactics/physics/charged/lect.html




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