Physics Basics Flashcards

Question

what are properties of X-rays

Answer 1

``` • Form of electromagnetic radiation ○ No mass ○ No charge ○ Very fast ○ Can travel in a vacuum etc ``` * Undetectable to human senses * Man-made • Cause ionisation ○ Ie displacement of electrons from atoms / molecules ○ It is this process that causes the dangerous side effects that humans can have when they are exposed to too much radiation

Answer 2

gamma rays are identical except that they occur naturally (& generally have higher energies) Gamma rays are created by radioactive decay

Answer 3

• Electrons fired at atoms at very high speed • On collision, the kinetic energy of these electrons is converted to electromagnetic radiation (ideally X-rays) and heat ○ Depending on their speed they can form other types of electromagnetic radiation ○ Heat is a side effect • The x-ray photons are aimed at a subject

Answer 4

building blocks of matter

Answer 5

○ Central nucleus § Protons - positive charge § Neutrons - neutral ○ Orbiting "shells" § Electrons - negative charge

Answer 6

neutrons and protons have a relative mass of 1 (they have equal mass) electrons essentially have no mass at all

Answer 7

collection of nucleons Protons and neutrons have similar mass Overall positive charge

Answer 8

number of protons Unique to each element Eg all carbon atoms will have 6 protons

Answer 9

number of protons and neutrons This number can change even for the same element Even though the element has the same number of protons, can have different numbers of neutrons in the same atom

Answer 10

the chemical properties of an atom

Answer 11

An atom in its "grounded state" is neutral Number of electrons = number of protons

Answer 12

Ionisation = removing / adding electron(s) to an atom Atom removing an electron = positive ion Atom gaining an electron = negative ion

Answer 13

Electrons spin around the nucleus in discrete orbits / shells electrons cannot exist between these shells Electrons try to fill available spaces in the inner shells first

Answer 14

Innermost shell is K | Then L, M, N, O, etc

Answer 15

``` K = 2 L = 8 M = 18 N = 32 ``` • Maximum number = 2n^2 Where "n" is the shell number § K = 1 § L = 2 etc Example: M shell is 3 --> 2 x 3^2 = 18

Answer 16

electrostatic force | Negative charge of electrons attracted to overall positive charge of nucleus

Answer 17

To remove an electron from its shell, a specific amount of energy is required to overcome this attraction

Answer 18

Binding energy = additional energy required to exceed electrostatic force The closer the electron is to the nucleus, the greater the electrostatic force (& therefore binding energy) The more positively-charged the nucleus (ie higher Z), the greater the electrostatic force ○ Carbon (Z=6): K shell binding energy = 0.28keV ○ Tungsten (Z=74): K shell binding energy = 69.5keV

Answer 19

The amount of energy required to move an electron to a more outer shell equals the difference in the binding energies of the 2 shells

Answer 20

if an electron drops to a more inner shell than this specific amount of energy is released ie the difference in the binding energies of the 2 shells This is a different number from element to element due to the different number of protons in the nucleus

Answer 21

* Tube head * Collimator * Positioning arm * Control panel * Circuitry

Answer 22

Creates the x-rays

Answer 23

Metal window which the X-rays pass through

Answer 24

Lets you hold the tube head and position it as close to the patient as possible

Answer 25

Required to power the whole thing

Answer 26

Flow of electric charge, usually by the movement of electrons SI unit: amp (or ampere), A Measure of how much charge flows past a point per second

Answer 27

○ Direct current (DC) = constant unidirectional flow (one direction) § Eg batteries ○ Alternating current (AC) = flow repeatedly reverses direction [Electron going one way then back again] It doesn’t matter what direction the current is going in as long as there is current going

Answer 28

Flow periodically reverses direction Number of complete cycles (reverse and reverse back) per unit time is the frequency ○ SI unit: hertz, Hz (cycles per second) ○ 1 hertz = 1 cycle per second Eg: mains electricity (50Hz in UK) current goes in forward direction, becomes more and more powerful before starting the become weaker current then flips and goes in a backward direction and gets more and more powerful before then becoming weaker before it flips again

Answer 29

• X-ray production requires a unidirectional current (DC current) But x-ray units are powered by mains electricity (AC) • X-ray units have generators which modify the AC so that it mimics a constant DC = Process is known as rectification

Answer 30

Difference in electrical potential between 2 points in an electrical field {Basically the difference between a negatively charged point in one place and a positively charged point in another} Related to how forcefully a charge will be pushed through an electrical field SI unit: volt, V

Answer 31

"potential difference"

Answer 32

• Mains supply in UK ○ Alternative current (<13 amps) ○ 220-240 volts • Dental X-ray unit ○ Requires direct current

Answer 33

Transformers alter the voltage (& current) from one circuit to another

Answer 34

○ Mains --> X-ray tube (cathode-anode) § Takes the mains supply and changes it so it is appropriate for the x-ray tube ○ Mains --> filament Takes the mains supply and changes it so it is appropriate for the filament

Answer 35

Increase potential difference across X-ray tube Usually 60,000-70,000 volts (60-70kV) Current reduced to milliamps (mA)

Answer 36

○ Decrease potential difference across filament § Around 10 volts § Around 10 amps

Answer 37

Made up of millions of X-ray photons directed in the same general direction

Answer 38

Photons effectively travel in straight lines but diverge from the X-ray source (ie do not travel in parallel)

Answer 39

its intensity

Answer 40

Quantity of photon energy passing through a cross-sectional area of the beam per unit time

Answer 41

Increase number of photons and / or energy of photons = increase intensity

Answer 42

Proportional to current in filament (mA) and potential difference across X-ray tube (kV) - Intensity is related to the current in the filament (as increasing the current will result in more photons) - Also related to the potential difference / voltage across the X-ray tube as this will result in photons with higher energies

Answer 43

Dose decreases with distance from X-ray source

Answer 44

To help work out how much you can cut down the radiation received from a source by standing further away

Answer 45

Intensity of X-ray beam is inversely proportional to the square of the distance between the X-ray source and the point of measurement therefore, doubling the distance will quarter the dose i dont know how to do that little symbol that is acc in the square law so look it up sorry its intensity {funny symbol} 1/distance^2

Answer 46

- Doubling the distance away from the source will quarter the dose received - Starting at 1metre from source then moving 4metres from the source the patient has doubled their distance twice ○ Doubled from 1 to 2 metres ○ And again from 2 to 4 metres - Double distance twice = quarter the dose twice ○ Start at 4 grays and quarter this once to get to 1 gray ○ Then quarter 1 gray to get to 0.25 grays Answer: 0.25 Gy (or 250 mGy) [maths way] Intensitya X distancea^2 = 1 AND intensityb X distanceb^2 = 1 ``` Intensitya X distancea^2 = intensityb X distanceb^2 ○ 4 X 12 = ? X 4^2 ○ 4 = ? X 16 ○ ? = 4/16 ? = 0.25 Gy ```

Answer 47

``` Alpha particles (can't pass through paper) ``` ``` Beta particles (can pass through paper, can't pass through aluminium) ``` ``` Gamma rays (can pass through paper, aluminium and lead) ```

Answer 48

radioactive decay of unstable atoms