Docsity
Docsity

Prepare for your exams
Prepare for your exams

Study with the several resources on Docsity


Earn points to download
Earn points to download

Earn points by helping other students or get them with a premium plan


Guidelines and tips
Guidelines and tips

X-Ray Circuit & Tube: Questions and Answers for Medical Imaging Students, Exams of Microelectronic Circuits

A comprehensive set of questions and answers related to the x-ray circuit and tube, covering essential concepts in medical imaging. It explores the components, functions, and principles of x-ray production, including thermionic emission, filament heating, and the role of the anode and cathode. The document also delves into the importance of filtration, heat management, and electrical safety in x-ray tube operation. It is a valuable resource for students studying medical imaging, radiology, or related fields.

Typology: Exams

2023/2024

Available from 10/29/2024

Fortis-In-Re
Fortis-In-Re 🇺🇸

1

(1)

2.3K documents

1 / 14

Toggle sidebar

This page cannot be seen from the preview

Don't miss anything!

bg1
X-Ray Circuit & Tube Questions With Accurate Answers
How many steps are there to pressing the X-ray button? - Answer-Two
What does the first step of pressing the button do? - Answer-Puts the x-ray into "prep" mode
What happens in prep mode? - Answer-The filament heats
A cloud of electrons are emitted around the filament
What is the cloud of electrons around the filament called? - Answer-The space charge
What is the space charge? - Answer-Electrons leave the filament as a cloud.
This creates a net +ve (positive) around the very negative cathode
What happens when the exposure button is pressed? - Answer-High electrical kilovoltage is applied.
Electrons accelerate across the tube
What energy do electrons have when they accelerate across the tube? - Answer-Kinetic energy
How can the electrons travels freely across the tube? - Answer-They travel in a vacuum
Is the cathode positive or negative? - Answer-negative
Is the anode positive or negative? - Answer-positive
What is the anode target made from? - Answer-Tungsten
pf3
pf4
pf5
pf8
pf9
pfa
pfd
pfe

Partial preview of the text

Download X-Ray Circuit & Tube: Questions and Answers for Medical Imaging Students and more Exams Microelectronic Circuits in PDF only on Docsity!

X-Ray Circuit & Tube Questions With Accurate Answers

How many steps are there to pressing the X-ray button? - Answer-Two

What does the first step of pressing the button do? - Answer-Puts the x-ray into "prep" mode

What happens in prep mode? - Answer-The filament heats

A cloud of electrons are emitted around the filament

What is the cloud of electrons around the filament called? - Answer-The space charge

What is the space charge? - Answer-Electrons leave the filament as a cloud.

This creates a net +ve (positive) around the very negative cathode

What happens when the exposure button is pressed? - Answer-High electrical kilovoltage is applied.

Electrons accelerate across the tube

What energy do electrons have when they accelerate across the tube? - Answer-Kinetic energy

How can the electrons travels freely across the tube? - Answer-They travel in a vacuum

Is the cathode positive or negative? - Answer-negative

Is the anode positive or negative? - Answer-positive

What is the anode target made from? - Answer-Tungsten

What is the atomic number of tungsten? - Answer-

What force does the tungsten target exert on the electrons? - Answer-A strong positive force

What three things control thermionic emission? - Answer-Temperature

Material type

Surface area of coil

What three things does an x-ray tube provide? - Answer-A supply of electrons

The ability to move them at high speed

A way to change their direction

What is the mains for an x-ray circuit? - Answer-Mains AC 240v

How many circuits are there in an x-ray circuit? - Answer-Two.

An xray circuit

A filament circuit

Where does the voltage go first when the button is pressed? - Answer-It goes through an auto transformer

What are the role of the auto transformer? - Answer-It ensures that the voltage remains set at a constant level to compensate for any fluctuations

It allows different kV values to be selected

What does the filament transformer do? - Answer-It provides a means to reduce the supplied voltage by means of a step down transformer

How does the filament transformer reduce voltage? - Answer-It receives AC current in in primary winding

It has a secondary winding that has LESS turns

This ensures a turns ratio that allows it to step DOWN the voltage to the required level

Where does the AC current go in the main circuit once it has passed through the auto transformer and HT transformer? - Answer-The AC current goes into the rectifiers

What is the role of the rectifiers? - Answer-To change the current from AC to DC

This ensures that the cathode is negative and the anode is positive

This ensures that electrons always travel from cathode to anode to PRODUCE XRAYS!!!!!!!

What are the two components of the xray tube? - Answer-The insert and the shield

What is the tube made from? - Answer-Borosillicate glass

What are the functions of the borosillicate glass tube? - Answer-Strong to support a vacuum

Allows thermal expansion to stop it cracking using seals made from different glass

Good electrical insulator

Rounded to prevent static

Radiolucent to transmit the beam(some is filtered)

Whats are the functions of the tube shield(housing) - Answer-Shock resistant

Radiation is sealed (lead lined 3mm)

Insulated

Well cooled

Built in filtration to remove low energy beams

What is the minimum total filtration that must be built into the xray tube shield? - Answer-2.5mm aluminium equivalent

What does the cathode operate at? - Answer-High negative potential

What does the cathode contain? - Answer-Filament

Focussing cup

wires and support

What is the focussing cup in the cathode made from? - Answer-Nickel or stainless steel

How is the focussing cup able to reduce the focal spot? - Answer-By using a negative bias

What are the features of the filament? - Answer-Made from tungsten

Low work function(4.5 ev) allows easy emission of electrons

High melting point

Low vapour pressure - doesnt evaporate

The stem contacts oil which uses convection to heat the oil

The oil expands and can cause expansion bellows to trip a microswitch preventing further xray exposures until cool down.

Heat from the oil passes through the metal casing via conduction

How can heat loss be maximised in the anode? - Answer-High conductivity material used

Large anode block

Anode length as short as possible

Anode stem in oil

Why is lead used on the outside of the casing? - Answer-It has a high atomic number (82) and provides good radiation protection

How is electrical safety achieved in the xray tube housing? - Answer-Live components are insulated using oil.

Components are earthed using copper wire braiding

Access to live components is restricted

Name the two types of filtration that protects against radiation within the xray tube? - Answer-Inherent filtration: glass and oil

Added filtration: aluminium

How is the xray tube designed to as small a radiation source as possible? - Answer-Using electron beam focussing

Target angulation

What faults can occur with the xray tube? - Answer-The filament will eventually break due to vaparisation

Oil seal and shield could leak

Glass may break and stress fracture

Heat can reduce xray efficiency over time

Glass insulating properties can reduce over time

How does an x-ray tube provide the means for x-ray production? - Answer-It provides :

A supply of electrons

A way to get the electrons to travel at high speed

A force that causes them to change directions

What energy does an a x-ray tube change? - Answer-Electrical energy into x-ray energy

What happens when electrons collide with atoms? - Answer-99% are lost to heat, 1% produce x-rays

What is electrons moving at high speed called? - Answer-Thermionic emission

How is an exposure made? - Answer-Turn on machine

Set kVp

Set mA

Set time

Press switch

Voltage is supplied across the tube

Electrons are accelerated across the tube

X-rays are produced

Why is tungsten used as the target - Answer-1) Low Vapour pressure(5000 kPa) - otherwise will become a conductor

  1. High melting point -3370c - Gets very hot when bombarded with electrons at high speed

  2. High atomic number - 74 - This increases the number of positive protons creating a greater positive attraction. Efficient converter of xrays

  3. Same thermal conductivity as Copper - Expansion rate is similar so doesnt get distorted when heat is applied

5 )Good Thermal conductor- Transfers heat to the Copper

Temperature increase of the target material in a stationary anode X-ray tube must be reduced to save the tube life. This can be achieved by: - Answer-reducing the mA

Copper is used to make the anode block because of its - Answer-High thermal conductivity

The glass envelope of an X-ray tube - Answer-insulates the anode from the cathode

The anode angle of a diagnostic X-ray tube - Answer-influences the size of the effective focal spot

The focal spot size of an x-ray tube influences - Answer-the unsharpness of the image

The mA is - Answer-the voltage between the filament and the anode of the x-ray tube

Tungsten is used as the target material in an X-ray tube because it has - Answer-a high atomic number

The oil in the X-ray tube housing - Answer-provides a method of heat dissipation

Lead is incorporated into the housing of an x-ray tube because - Answer-it has a high atomic number

An x-ray tube converts electrical energy directly into x-rays and - Answer-heat

In an X-ray circuit the high tension transformer - Answer-is used to raise the value of the mains supply voltage

Tungsten wire is used for the filament of the X-ray tube because it - Answer-Low vapour pressure so doesnt evaporate

Low work work function (4.5eV)

Easily emits electrons

Very strong & can be drawn into a thin spiral of wire to increase surface area - DUCTILE

Copper is used in a stationary anode x-ray tube because - Answer-it is a good conductor of heat

The tungsten target of an X-ray tube - Answer-is bombarded by electrons during the exposure

How can heat be reduced in a tube - Answer-Reducing kVp, mA & time

What is the inherent filtration - Answer-Glass envelope

Oil

What is the added filtration - Answer-Aluminum

What reduces spot size - Answer-Light beam diaphragm

Three principles of electrical safety - Answer-Live components insulation

Component housing earthing

Restricted access to live components

What is the area bombarded by electrons - Answer-True focal area

The area below the true focal area - Answer-Effective spot size

What does the rotating anode achieve - Answer-Spreads heat

What faults can occur with the x-ray tube - Answer-Tungsten deposits reducing vacuum

Glass may be broken/fractured

Filament may break

Oil seal leakage

Heat causes crazing on anode causing unsharpness

Tube shield construction requirements - Answer-No danger of shock

Radiation must not escape

Support for tube & cables

Insulation between insert & shield

Cooling

Filtration

Why use a focussing cup - Answer-Plume of electrons will increase in size as they travel