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physics > P6 - radioactivity > Flashcards

P6 - radioactivity Flashcards

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1
Q

what is the absorption spectrum?

A

a continuous spectrum with dark lines where particular wavelengths/frequencies of EM waves have been absorbed

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2
Q

what is the atomic number?

A

number of protons in a nucleus

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3
Q

what is background radiation?

A

radiation from all around us including the air, rocks, the sun, space and artificial sources

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4
Q

what is a chain reaction?

A

a reaction where the product of the first reaction causes further reactions to take place

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5
Q

what is contamination?

A

having a radioactive source (material) inside the body or on the skin

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6
Q

what is decay?

A

a random process by which an unstable nucleus loses energy by emission of radiation or a particle

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7
Q

what is the emission spectrum?

A

a set of wavelengths/frequencies of EM waves emitted by an atom when excited electrons move to lower energy levels

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8
Q

what is nuclear fission?

A

the process of splitting a heavy nucleus to form two or more small nuclei, releasing large quantities of energy

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9
Q

what is nuclear fusion?

A
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10
Q

what is half-life?

A

the half-life of a radioactive element is the time that it takes half the nuclei in a sample to decay

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11
Q

what is ionisation?

A

the gain or loss of electrons from an atom, leaving it charged

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12
Q

what is irradiation?

A

being exposed to radiation from a source (usually external)

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13
Q

what is an isotope?

A

atoms with the same number of protons and electrons but different numbers of neutrons

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14
Q

what is the mass number?

A

number of protons + number of neutrons

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15
Q

what is a nucleon?

A

a proton or neutron

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16
Q

what are the four types of radiation which a nucleus will spit out when it decays?

A
  • alpha
  • beta
  • gamma
  • neutron
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17
Q

what is an alpha particle?

A
  • 2 neutrons and 2 protons (same as a helium nucleus)
  • relative mass of 4 and charge of 2
  • relatively big and heavy and slow moving
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18
Q

what is a beta particle?

A
  • an electron
  • virtually no mass and charge of -1
  • move quite fast and quite small
  • for every beta particle emitted, a neutron turns to a proton in the nucleus
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19
Q

what is a gamma particle?

A
  • a type of electromagnetic wave
  • no mass and no charge
  • just energy
  • don’t change element of nucleus that emits them
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20
Q

why might a nucleus emit a neutron?

A

if a nucleus contains a lot of neutrons, it may just throw out a neutron

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21
Q

what happens when radiation travels through a material?

A

it can collide with the material’s atoms, which slows down or stops the radiation; this means that the radiation can only penetrate so far into a material before it’s absorbed

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22
Q

what does the range of radiation depend on?

A

the type of radiation and material it’s travelling through

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23
Q

rank the different types of radiation on their penetration properties? (most to least)

A
  1. gamma
  2. beta
  3. alpha
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24
Q

what is the count rate?

A

the number of radioactive particles that reach a detector in a given time

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25
Q

why does the count rate decrease the further from the detector is from a radioactive source?

A

the further the radiation has to travel, the higher the chance it will be absorbed by the material it is travelling through

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26
Q

what are alpha particles blocked by?

A

paper

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27
Q

what are beta particles blocked by?

A

thin aluminium

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28
Q

what are gamma particles blocked by?

A

thick lead

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29
Q

what happens to a nucleus when it emits an alpha particle?

A
  • the mass number decreases by 4
  • the atomic number decreases by 2
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30
Q

what happens to a nucleus when it emits a beta particle?

A
  • the mass number doesn’t change
  • the atomic number increases by 1
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31
Q

what happens to a nucleus when it emits a gamma ray?

A
  • the mass number and the atomic number don’t change
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32
Q

why will a new element be formed in both alpha and beta emissions?

A

the number of protons changes

33
Q

what do electrons in an atom sit in?

A

different energy levels or shells

34
Q

how far from the nucleus are the energy shells?

A

each energy shell is a different distance from the nucleus

35
Q

how can an inner electron move up one or more energy levels in one go?

A

if it absorbs electromagnetic radiation with the right amount of energy; when it does move up, it moves to a partially filled (or empty) shell

36
Q

what is an electron said to be when it moves to a higher energy level?

A

excited

37
Q

what happens when an electron the falls back to it’s original energy level?

A

it will lose the same amount of energy it absorbed; the energy is carried away by EM radiation

38
Q

what does the part of the EM spectrum that the radiation is from depend on?

A

its energy (which depends on the energy levels the electron moves between)

39
Q

what does a higher energy mean for the frequency of EM radiation?

A

higher energy means higher frequency of EM radiation

40
Q

when is an atom ionised?

A

an atom is ionised if it loses an electron

41
Q

what happens when an atom is ionised?

A
  • if an outer electron absorbs radiation with enough energy, it can move so far that it leaves the atom
  • it is now free and tom is said to have been ionised
  • atom is now positive ion
  • it’s positive because there are more protons than electrons
  • atom can lose more than one electron
  • the more electrons it loses, the greater its positive charge
42
Q

what can ionise atoms?

A

nuclear radiation

43
Q

what is ionisation power?

A

a measure of how likely it is that radiation will ionise an atom

44
Q

which radiation has the highest ionisation power?

A

alpha particles

45
Q

what does it mean that alpha particles have the highest ionisation power?

A

it means that they can’t travel very far through a substance without hitting an atom and ionising it

46
Q

what do fluorescent tubes contain?

A

mercury vapour

47
Q

how do fluorescent tubes use excited electrons to produce light?

A
  • electrons are accelerated through the mercury vapour, which ionises some of the mercury atoms, producing free electrons
  • when this flow of free electrons collides with electrons in other mercury atoms, the electrons in the mercury atoms are excited to higher levels
  • when these excited electrons return to their original energy levels, they emit radiation in the ultraviolet range of the electromagnetic spectrum
  • a compound called phosphor coats the inside of the tube and absorbs the radiation, exciting its electrons to higher energy levels; these electrons then cascade down the energy levels, emitting many different frequencies of radiation, all in the visible part of the electromagnetic spectrum
48
Q

what happens to the radioactivity of a sample over time?

A

it decreases

49
Q

why can’t you predict when a particular nucleus is going to decay?

A

radioactive decay is a random process

50
Q

information about decaying radioactive isotopes?

A

radioactive isotopes decay at different rates

51
Q

what is activity and what is it measured in?

A

the number of unstable nuclei that decay in a given time is called the activity and is measured in becquerels (Bq) - the number of nuclei that decay each second

52
Q

what is used to detect the radiation emitted from a decaying nucleus?

A

a Geiger Muller tube

53
Q

what does the Geiger Muller tube measure?

A

the count rate in counts per minute (or per second)

54
Q

why does a short half-life mean the activity falls quickly?

A

because lots of the nuclei decay in a short time

55
Q

why does a long half-life mean the activity falls more slowly?

A

because most of the nuclei don’t decay for a long time - they just sit there, basically unstable, kind of biding their time

56
Q

what are two things that can be used to calculate half-life?

A
  1. numbers
  2. a graph
57
Q

what can ionising radiation harm?

A

living cells

58
Q

what happens when some materials absorb ionising radiation?

A

it can enter living cells and interact with molecules

59
Q

what is caused by the interactions with molecules that occur when ionising radiation enters living cells?

A

ionisation (they produce ions)

60
Q

what results from lower doses of ionising radiation?

A

lower doses damage living cells by causing mutations in the DNA which can cause the cell to divide uncontrollably (which is cancer)

61
Q

what can occur from higher doses of ionising radiation?

A

higher doses tend to kill cells completely, which causes radiation sickness if a lot of cells all get blasted at once

62
Q

which radiation is the most dangerous OUTSIDE the body?

A

beta and gamma sources because they can still get inside to the delicate organs (they can pass through skin)

63
Q

why is alpha less dangerous than beta or gamma outside the body?

A

it can’t penetrate the skin

64
Q

which radiation is the most dangerous INSIDE the body?

A

an alpha source is the most dangerous because they’re the most ionising and they do all their damage in a very localised area

65
Q

why are beta and gamma less dangerous than alpha inside the body?

A

they are less ionising and gamma will mostly pass straight out without doing much damage

66
Q

what risks do all radioactive sources have?

A

irradiation and contamination risks

67
Q

what do the hazards associated with a radioactive source depend on?

A

it’s half-life

68
Q

what are some uses of radioactivity?

A
  1. smoke detectors
  2. thickness detecting
  3. treating cancer (radiotherapy)
  4. sterilisation
  5. leak locating
  6. medical tracers
69
Q

how do smoke detectors use radioactivity?

A
  • alpha particles are used in smoke detectors
  • alpha radiation should ionise air inside the detector and create a current
  • the alpha emitter is blocked when smoke enters, causing the alarm to be triggered by a microchip when the sensor doesn’t detect alpha
70
Q

how does thickness detecting use radioactivity?

A
  • if the paper is too thick, less beta radiation is detected because more is absorbed
  • the rollers are then automatically told to move closer together (opposite is also true)
  • use beta (all alpha would get blocked and all gamma would get through regardless of thickness)
  • vey long half-life; otherwise count would decrease and make the computer think the paper had become too thick
71
Q

how does radiotherapy/treating cancer use radioactivity?

A
  • an x-ray or gamma source is rotated around a person’s body, continuously aiming the x-rays/gamma at the tumour
  • this ensures the tumour gets a large amount of radiation (and hopefully the cells die) whilst surrounding healthy cells receive the lowest amount possible (so that they don’t get damaged or killed)
72
Q

how does sterilisation use radioactivity?

A
  • gamma radiation can be used to kill bacteria on medical equipment and fresh food
  • this prolongs the life of food by slowing biological decay
  • this does not make food radioactive at all
  • makes old food look fresh but nutritional content decreases over time
73
Q

how does leak locating use radioactivity?

A
  • a radioactive tracer is put into an underground water pipe to locate a leak
74
Q

what radiations are emitted from the medical tracers we use/why?

A

beta or gamma; isotopes of iodine only have beta

75
Q

why is alpha never used for medical tracers?

A

alpha is highly ionising and not very penetrative (couldn’t be detected)

76
Q

how do we get medical tracers into the patient?

A

inject, ingest, inhale

77
Q

why is it good that radioactive iodine behaves the same as non-radioactive iodine?

A

the body will function normally (wouldn’t reject it etc)

78
Q

do we want a long or short half-life for medical tracers/why?

A

short half-life (abt 4-6 hours)
- so it can be transported and still be radioactive
- also don’t want it continuously emitting radiation within the body

physics (11 decks)

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