chemistry for dose reduction

Question 2

define luminescence

Answer 2

light emission thats not caused by heating

Question 3

define chemoluminescence

Answer 3

emission of light after a chemical reaction

Question 4

define photoluminescence

Answer 4

when a chemical glows after being exposed to photos of light or x radiation

Question 5

what is the difference between the electrons in an atom of gaseous and crystallin form?

Answer 5

gasesous:
- electrons have distinct separation between the orbits
- transitions known as Discrete

crystalline:
- electrons have energy levels which blur into bands
- making it easier for electrons to move between the levels

Question 6

describe the type of energy band that insulators and semi conductors have + how it affects its function

Answer 6

insulators = energy band with large gaps need a lot of energy to move an electron between them

semi-conductors = energy band closer together need less energy

bands in contact or overlap can conduct electrons easily

Question 7

how is coloured light formed when incident photon hits a bound electron

Answer 7

photon is absorbed and gives energy to electron

difference in energy bands between crystalline structures leads to colour sensitivity
or
emission of coloured light (when electron returns from higher state to original state releasing energy)

wavelength of energy causes colour (red for longer, blue for shorter)

Question 8

why does each atom have specific coloured light emission

Answer 8

because in order for the emission to occur, the incident photon must have exactly the right energy to cause the electron energy level change

Question 9

what does PSP stand for

Answer 9

photostuimuable storage phosphor

Question 10

what is a light-emitting phosphor crystal / storage crystal

Answer 10

reacts to XR where electrons are given energy to change band

Question 11

why is a latent image formed in light emitting phasor crystals

Answer 11

electrons are trapped in electron ‘holes’ within the crystal so they dont immediatly fall back into their lower state for ming the latent image (not yet visible)

Question 12

where are PSP’s used and how

Answer 12

CR imaging, coating the plate inside the cassette

used to store image and retrieve it after

Question 13

what are photostimuable phosphors made out of

Answer 13

barium attached to any halide to form e.g flurohalide, bromohalide

Question 14

why do PSP’s contain europium

Answer 14

to dope it with holes in order to form the latent image by trapping electrons

Question 15

what are the 8 layers of a CR plate

Answer 15

• front protective layer
• phosphor layer
• reflective layer
• electroconductive layer
• polyester base layer
• light shielding layer
• back protective layer

Question 16

why are phosphors preferably used

Answer 16

capturing image by turning xray into light is more efficient and lowers the dose to patient

Question 17

what are 2 commonly used phosphors used in each DR and CR

Answer 17

DR: CSi:Na (blue) , CsI:Tl (yellow)

Cr: BaFBr:Eu (blue), CsBr:Eu (blue)

Question 18

why is fluorescence used

Answer 18

live imaging

no delay

Question 19

describe process of fluorescence

Answer 19

incident photon removes bound electron from k-shell

higher energy electron fills the vacancy

as higher electron returns to ground state, it releases energy in form of light

Question 20

where is scintillation usee

Answer 20

in XR flat detectors (DR and flat panel fluroscopy)

Question 21

what are the advantages of scintillators

Answer 21

• create high-resolution digital images at low dose
• scintillator array phptodetectors are more sensitive tour than phosphorescent and fluorescent mechanisms

Question 22

describe the structure os scintillators and how this is an advantage

Answer 22

fine crystals grown for high resolution and minimal scatter of light between them

Question 23

where can scintillators be found

Answer 23

• gamma cameras in NUCLEAR MEDICINE
• very modern CT scanners
• DR and Flat panel fluroscopy