Natural Radoactivity

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Nuclear physics

Unit 2


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Unit 2

Principles of Nuclear Physics Natural radioactivity,

Decay series, type of radiation and theirapplications.

Radioactive Decay Spontaneous Emission

Isometric Transition - Gamma ray emission, alpha,beta, positron decay, electron capture

Production of radionuclides Cyclotron produced

Radionuclide - Reactor produced Radionuclide fission and electron Capture reaction, Radionuclide

Generator Milking Process - Linear accelerator

Radionuclide used in Medicine and technology


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1895 - Wilhelm Roentgen Discovered X-rays on

8th November 1895 The World

immediately realised

Won Nobel Prize in1901


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X-rays was quickly put to clinical use


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1896 - Henri Becquerel

Discovered

radioactivity on26 February1896

Some atoms give offenergy in form of rays.Uranium gives ofradiation.

Shared Nobel Prize in1903 with P. Curie.


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1896 - Henri Becquerel

radioactivity blackens a

photographic plate eventhrough a layer of black

paper


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Natural radioactivity In 1896 Henri Becquerel

discovered that uraniumsalt emits radiations evenin dark , which penetratesthe paper and affect the

After the discovery of

Becquerel, lordRutherford and Villard ,found that theseradioactive radiations are

photographic plates. Later , it was found that

not only uranium , othersubstances like Thorium ,

radium , polonium andactinium emittedradiation.

of three types


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Three types of radiation The first one:

Very soft , easilyabsorbed and capableof producing intense

The third one :

This one was still morepenetrating than the and rays ( rays)

The second one :

More penetrating than rays and less effectiveas ionizing agent (rays)


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Madame curie The existence of these

radiation wasdemonstrated by

Madame curie by a

, and rays

simple experiment : LEAD block -> radium ,

photographic plate

Strong magnetic field isapplied at right angles

to the plane.


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Properties of rays An alpha particle consists

of two neutrons and twoprotons ejected from the

nucleus of an atom.

In air, their travel

distances are limited tono more than a few

centimeters.

e a p a par c e sidentical to the nucleus of

a helium atom.

Examples of alpha emitters

are radium, radon,

thorium, and uranium.

alpha particles can be

stopped by a single sheet

of paper


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Properties of ray Alpha particles are

positively charged Their velocity ranges

from 1.4 * 10 to 2.3 *

From uranium ->

decay the velocity is 1.4* 10 m/s

Thorium -> decay the

10 m/s The velocity depends

upon the radioactive

substance from whichthey are ejected

velocity is 2.3 * 10 m/s


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Properties of ray They produce

ionization in the gasthrough which theypass .

They affect a

photographic plate. Theeffect is feeble.

They produce

100 times greater than rays and 10000times greater than

rays

substance like zincsulphide, Bariumplatinocyanide.

They are nuclei ofhelium atom He


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Properties of ray Effect by electric field :

When the beam ofradioactive radiation issubjected to an electric

Effect by magnetic field :

If a magnetic field isapplied perpendicularto the plane , the

plates , the particlesare deflected towardsthe negative plate.

This shows particlesare positively chargedparticles .

towards left.


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They produce heating

effect The body suffers

incurable burns when

exposed to - Rays They are stopped in a

sheet of paper or 7 cm

of air.


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Properties of -Rays They have high velocity

ranging from 1 to 99 % ofthe velocity of light

They produce ionizationin air but the no of ions

For eg: they can easilypass through 1 cm of hickaluminum sheet. Theystopped in a few mm oftissue.

those of rays. Because of their small

mass , they penetratethrough large thickness of

matter.

photographic plate andtheir effect is greater than rays.

They are affected by

electric and magneticfield.


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Properties of -Rays rays are electrons ,

no change in massnumber , the atomic

number is increased by

1 They produce

fluorescence in

substance like cadiumtungsten, Barium

platinocyanide


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Properties of rays The velocity of rays

is the same as that oflight (3*10 cms / sec)

They produce ionization

They are electro

magnetic radiation likex-rays

They have very high

in gases through whichthey pass but their

effect is very small

when compared to thatof rays and - rays

photon energy (ie) Mev. They are unaffected by

electric and magnetic

field.


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Properties of rays They are more

penetrating than -rays and can pass very

easily through 30 cms

Penetrating distances

thickness of iron. Absorbed exponentially

in many cm of tissue.


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Difference between X-rays and Gamma

rays

rays are produced

spontaneously byradioactive emission

whereas x-rays are

X-rays are emitted from

the outer orbit while rays are from the

nucleus

given out by thetransition of electrons

from higher to lower

energy level.

The wavelength of rays is much shorter

than the wavelength of

X-rays.


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Difference between X-rays and

Gamma rays The penetrating power

of rays are muchhigher than X- rays.

rays can penetrate

whereas x-rays consist of

three components hard, medium and soft x-

rays.

through 30 cm of thickiron sheet.

rays are

monochromaticelectromagnetic

radiation.

The most useful radionuclides for nuclear

medicine are those that

emit gamma rays .


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Alpha Particles ()

Large Particle = 2p + 2n (like Helium atom)

positively charged Low speed

Less energy,

Non-penetrating Range: short (mm in air and few microns in tissue)

not used for Nuclear Imaging

will ionize the matter through which it is passing

proposed ofradiation therapy


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Beta Particles ()

Small particle

Negatively charged e

-

( -

) Positively charged e+ ( + ) - Positron

High speed

Range: Large (cm- m in air)

Tissue: few mm

Used for radiation therapy

Biological Hazards:external and internal

Radio nuclides : 32p- Liver,


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Gamma radiation () High frequency Electromagnetic radiation

Photons/x-rays

Energy : 50Kev to 3Mev Penetrating radiation

Range: Large (several meters in air and few cm in tissue)

Shielding: Lead, other metals

external and internal Used for both imaging and therapy

Fixed energy

For imaging 60 to 511Kev

Radionuclide :51

Cr (Red blood cells),131Ba (intestinal),131I (Thyroid),99m Tc (Brain,Cardiac)


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Radio activity There are two types of radioactivity

1. Natural RadioactivityMost naturally occurring radioactive isotopes are not

clinically useful (long T1/2).

2. Artificial RadioactivityArtificial radioactive isotopes produced by bombarding

stable isotopes with high-energy photons or charged

particlesNuclear reactors (n), charged particle accelerators

(Linacs, Cyclotrons)

Natural Radoactivity

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