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PHYS3008: Health Physics > Lecture 14 > Flashcards

Lecture 14 Flashcards

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1
Q

Define non-ionising radiation

A

Any type of radiation less than the ionising potential (including visible light and UV light). It is less energetic than ionising radiation.

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2
Q

What is meta-stable state?

A

A particular excited state of an atom, nucleus, or other system that has a longer lifetime than ordinary excited states and (generally) a shorter lifetime than the ground state.

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3
Q

What is a population inversion?

A

A state of a system in which there are more members of the system in higher states than in the lower, unexcited states.

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4
Q

How does a LASER work?

A

A narrow beam of light is produced in which all photons have the same wavelength.

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5
Q

What is laser surgery and how does it work?

A

High-power, very focused beams of infrared light are directed at a target in the body using a carbon dioxide laser. These beams vaporise the tissue (tissue ablation).

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6
Q

Give an example of when lasers are used in healthcare.

A

UV lasers are used for corrective eye surgery by emitting very powerful but short pulses of light.

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7
Q

What is a negative side effect of laser surgery?

A

The high power of the laser can cause unwanted damage to the skin, corneas, lens or retina. The greater the light intensity, the more photochemistry occurs and the more damage happens as a result.

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8
Q

What is the maximum permissible exposure (MPE) for ocular exposure to visible light?

A

For a 400 - 700 nm wavelength, the continuous (1hr) limit is 1 mW/cm².

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9
Q

What is the maximum permissible exposure (MPE) for ocular and skin exposure to HeNe (632 nm)?

A
  • Occular: 2.5 mW/cm² for a 0.25s blink reflex
  • Skin: 200 mW/cm² for 1hr
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10
Q

What are the class categories for lasers?

A

Class 1
Class 1C
Class 1M
Class 2
Class 2M
Class 3R
Class 3B
Class 4

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11
Q

What are the allowed powers for the 4 main laser categories?

A

Class 2: 0-1 mW
Class 3R: 1-5 mW
Class 3B: 5-500 mW
Class 4: 500+ mW

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12
Q

What is the wavelength of UVA?

A

320 - 400 nm

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13
Q

What is the wavelength of UVB?

A

280 - 320 nm

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14
Q

what is the wavelength of UVC?

A

100 - 280 nm

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15
Q

What is the energy of UVA at 400nm (in eV)?

A

3.1 eV

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16
Q

What is the energy of UVB at 320 nm (in eV)?

A

3.9 eV

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17
Q

What is the energy of UVC at 280 nm (in eV)?

A

4.4 eV

18
Q

Rank UV radiation from least to most ionising

A

UVA
UVB
UVC

19
Q

What are sources of UV radiation?

A
  • Mercury lamps
  • Black light lamps
  • Laser
  • LED
  • Arc lamps and welding
20
Q

A fluorescent tube is a __ _______ source.

A

UV radiation

21
Q

How do fluorescent tubes work?

A

They rely on the inelastic scattering of electrons. The electrons collide with atoms in the gas which causes a temporary jump of one of the gas electrons to a higher energy level and light is emitted when they return to their original state.

22
Q

What are the wavelengths of fluorescent light?

A

253.7 nm to 185 nm

23
Q

Give two examples of UV detectors

A
  • Semiconductor devices (cheap and sensitive)
  • Thermopile (true radiometric measurements)
24
Q

How do semiconductor diode devices detect UV?

A

1) The n-type semiconductor acts as a detector of photons.
2) Incoming photons are prevented from recombining with the material by an imposed electric field, generating electron-holes pairs.
3) A current flows proportionally to the incident photon flux, showing the location of the beam.
4) The p-type semiconductor acts as a voltage multiplier so that the location of each photon is clearer.

25
Q

How do thermopiles work to detect UV?

A

Incoming radiation heats a junction, generating a voltage that can then be used to determine the location of the photon. This uses the thermoelectric effect.

26
Q

What is the outer waterproof layer of skin made of?

A

Dead cells

27
Q

What type of light is required to synthesise vitamin D in the skin?

A

UV light

28
Q

How is melanin pigment produced?

A

The pigment production is stimulated by UVB as a protection response to DNA damage.

29
Q

What are the benefits of melanin?

A

It is an absorber of UV so plays a protective role in the skin.

30
Q

What are negatives of UV radiation?

A
  • UVA, UVB, and UVC all damage collagen fibres which causes skin ageing.
  • UV radiation causes direct or indirect DNA damage so can lead to skin cancers.
31
Q

How does UV directly damage DNA?

A

It causes thymine bases on the same strand to bond to one another rather than across the helix. This is an example of single-strand damage.

32
Q

What is the main source of UV?

A

The Sun

33
Q

What is the total flux from the Sun?

A

1000 W/m²

34
Q

What is erythema?

A

Sun burn

35
Q

How long does it take for sunburn to occur?

A

15 mins

36
Q

What is a malignant melanoma?

A

The most serious type of skin cancer. There are 10000 cases reported per year and over 2600 deaths per year because of it.

37
Q

What is non-melanoma skin cancer?

A

The more common type of skin cancer. It is easily treated. There are 100000 cases per year.

38
Q

What % of non-melanoma skin cancer comes from UV radiation?

A

~90%

39
Q

What are the uses for UV radiation in healthcare?

A
  • Phototherapy: treatment of psoriasis and other skin conditions
  • Dental resins: curing due to UV illumination
  • Water treatment: killing bacteria
  • Attracting insects: to kill them
40
Q

What is photodynamic therapy (PDT)?

A

A type of therapy where non-toxic light-sensitive compounds are given to a patient either orally, injected, or topically. This compound is then exposed to light in certain areas to cause the compound to become toxic and kill the cells nearby.

41
Q

What is photodynamic therapy (PDT) used for?

A
  • Surgery
  • Dermatology (externally applied)
  • To kill tumours

PHYS3008: Health Physics (19 decks)

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