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Group Members

Omkar Mhapsekar

Sagar Newase

Sairaj Teli

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A bit of History

Will iam Roentgen dis co vered X-rays in 1895 . Roentg en w as award ed th e Nob el Prize in 1901.

X-ray have the following properties :-1. Travel in straight lines2. Are exponentially absorbed in matter with the

exponent proportional to the mass of the

absorbing material3. Darken photographic plates4. Make shadows of absorbing material on

photosensitive paper

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X-rays are electromagneticradiation of exactly the same

nature as light but of very muchshorter wavelength.

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X-ray are produced when acceleratedelectrons collide with the target. The loss of energy of electrons due to impactis manifested as x-rays. X-ray radiation produced in an x-ray tube.

Most of kinetic energy of electrons of theelectrons striking the target is converted intoheat , less than 1% being transformed into x-rays.

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Production of x-ray includes Glass enclosure , Cathodeand Anode

It is necessary to seal the twoelectrode of the x-ray tube invacuum.

The shape and size of these x-raytubes are specifically designed toprevent electric discharge betweenthe electrodes.

The connecting wires must besealed into the glass wall of the x-

ray tube .

During operation of x-ray tubeboth the glass and the connectingwires are heated to hightemperatures.

GLA SS ENCLOSURE :

Because of the difference in theircoefficients of expansion mostmetals expand more than glasswhen heated.

This difference in expansion wouldcause the glass metal seal to breakand would destroy the vacuum inthe tube if special precautions werenot taken.

Because of this problem, specialallows having approximately thesame coefficients of linearexpansion as pyrex lass aregenerally used in x-ray tubes.

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LINE FOCUS PRINCIPLE

NEED:-I. 99% energy is converted into heatII. Less than1% is converted into x-rayIII. Large focal spotIV. Small focal area

LINE FOCUS PRINCIPLE(1981):-I. Size and shape of focal spotII. Size and shape of electron stream

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LINE FOCUS PRINCIPLE

Target face is placed at angle about 5-20degree to cathode.

Actual focal spot size is increased.

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LINE FOCUS PRINCIPLEThe EffectiveFocal Spot is thebeam projectedonto the patient.

As the anode angledecreases, theeffective focal spotdecreases.

Diagnostic tubetarget angles rangefrom 5 to 15.

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ADVANTAGES

The advantage of Line focus is itprovides the sharpness of the small focalspot with the heat capacity of the largelarge focal spot.

Smaller target angles will producesmaller effective focal spots and sharperimages.

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LIMITATIONS Area covered by thebeam reduces withtarget angle

To cover a 17 theangle must be 12

To cover 36 the anglemust be 14

Anode heel effect .

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CATHODE AND ANODE

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Cathode

Cathode is a source of

electrons which consist offilament and focusing cup.

It supply both voltage andamperage.

It is made up of Tungstenwire of about 2mm indiameter.

Definition:-The negatively charged electrode by which electrons enter

an electrical device.

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As current flows through this finetungsten wire it becomes heated andcauses thermionic emission.

The electron cloud surrounding thefilament produced by the thermionicemission is called Edison Effect.

Space charge effect is also observedwhich has to limit the emission of moreelectrons from the filament.

Cont..

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AnodeDefinition:-

The positively charged electrode by which the electronsleave an electrical device.

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Anode consist of small plate of tungsten which is 2mm or 3mmthick.

Tungsten is used because it has high atomic number, melting

point.If Cu anode is used it acts to increase the total thermal capacity

of the anode and also increases rate of cooling.

The rotating anode principle is used to produce X-ray tubesCapable of withstanding the heat generated by large exposure.

The anode of rotating anode too consist of large disc of tungstenwhich rotates at 3600 rpm.

Cont..

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