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radioactivity Flashcards

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1
Q

describe an atom

A
  • positively charged nucleus consisting of protons and neutrons surrounded by negatively charged electrons
  • nuclear radius is much smaller than the atom
  • almost all the mass in the nucleus
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2
Q

Recall the typical size (order of magnitude) of atoms and small
molecules

A

1 times 10 to the power of negative 10 m

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3
Q

Describe the structure of nuclei of isotopes using the terms
atomic (proton) number and mass (nucleon) number and using
symbols in the format
13
C
6

A

top number is mass
bottom number is atomic

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4
Q

what is an isotope of an element

A

atoms with the same number of protons but different number of neutrons

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5
Q

what does the nucleus of each element have

A

a characteristic positive charge
(protons are positive and neutrons are neutral so overall positive charge)

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6
Q

what do isotopes of an element differ in

A

differ in mass by having different numbers of neutrons

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7
Q

what is the relative mass of protons

A

1

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8
Q

what is the relative electric charge of protons

A

+1

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9
Q

what is the relative mass of electrons

A

0.0005, negligible

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10
Q

what is the relative electric charge of electrons

A

-1

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11
Q

what is the relative electric charge of neutrons

A

0

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11
Q

what is the relative mass of neutrons

A

1

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12
Q

what is the relative mass of a positron

A

same as electron - 0.0005

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13
Q

what is the relative electric charge of a positron

A

positive +1 charge

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14
Q

why is an atom neutral

A

because the number of protons equals the number of electrons

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15
Q

what does an electron do in each atom

A

orbits nucleus at different set distances from the nucleus in shells

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16
Q

Explain that electrons change orbit when there is absorption or
emission of electromagnetic radiation

A
  • an inner electron can move up to a higher energy level (shell) if it absorbs electromagnetic radiation with the right amount of energy
  • excited electrons emit the same amount of energy it absorbed to return to their original energy level
  • this energy is carried away by EM radiation
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17
Q

why does and excited electron falling from the third energy level to the second release less energy than an excited electron falling from the second energy level to the first

A

as you move further out from the nucleus the energy levels get closer together (so difference in energy between two levels by each other gets smaller)

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18
Q

what does the part of the EM spectrum the radiation emitted from the atom dependent on

A

energy levels the electron moves between
a higher energy means a higher frequency of EM radiation
often visible light is released when electrons move between energy levels

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19
Q

Explain how atoms may form positive ions by losing outer
electrons

A

if an outer electron absorbs radiation with enough energy it can leave the atom and is now a free electron (ionised)
it is positive now because there are more protons than electrons
- the more electrons it loses the greater its positive charge

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20
Q

what are alpha, beta minus, positron, gamma rays and neutron radiation emitted from

A

unstable nuclei in a random process

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21
Q

what are alpha, beta minus, positron and gamma rays

A

ionising radiations

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22
Q

what is ionising radiation

A

any radiation that can knock electrons from atoms

23
Q

what is radioactive decay

A

when other unstable isotopes tend to decay into other elements and give out radiation as they try to become more stable

24
Q

Explain what is meant by background radiation

A

low level radiation that is around us all the time
- radioactivity of naturally occurring unstable isotopes in the air like in some foods, building materials, rocks
- radiation from space (cosmic rays) that come from the sun
- radiation due to human activity ex fallout of nuclear explosions and nuclear waste

25
Q

Describe the origins of background radiation from Earth and
space

A

earth - unstable isotopes all around us like some foods, building materials, and rocks
- human activity like nuclear explosions fallout or nuclear waste
space - cosmic rays mostly come from the sun but most of this is stopped by the Earth’s atmosphere

26
Q

Describe methods for measuring and detecting radioactivity
limited to photographic film and a Geiger–Müller tube

A

photographic film = more radiation the film’s exposed to the darker it becomes
Geiger–Müller tube = clicks each time it detects radiation, tube can be attached to a counter which displays the number of clicks per second (count rate)

27
Q

what is activity and what is it measured in

A

the rate at which a source decays and is measured in becquerels
activity can be measure by photographic film or with a Geiger–Müller tube

28
Q

what is an alpha particle equivalent to

A

a helium nucleus - two neutrons and two protons

29
Q

where is the beta particle emitted from

A

a beta particle is an electron emitted from the nucleus

30
Q

what is a gamma ray

A

a type of EM radiation

31
Q

compare alpha, beta and gamma radiations in terms of their abilities to ionise

A

alpha = strongly ionising
beta = both plus and minus are moderately ionising
gamma = weakly ionising

32
Q

Compare alpha, beta and gamma radiations in terms of their
abilities to penetrate

A

alpha = not very penetrating and are stopped quickly, can only travel a few cm in air and are absorbed by a thin sheet of paper
beta = positrons have a smaller range because of annihilation, beta-minus have a range of a few metres and are absorbed by a sheet of aluminium paper (around 5mm)
gamma = penetrate far into materials without being stopped and will travel a long distance through air, can be absorbed by thick sheets or lead or metres of concrete

33
Q

Describe how and why the atomic model has changed over time

A
  • plum pudding model suggested that atoms where spheres of positive charge with tiny electrons stuck in them
  • Rutherford fired beams of alpha particles at a thin gold foil and some were deflected back = so most of atom’s mass was at the centre of a tiny nucleus and most of the atom was tiny space, and that atoms must be positively charged as it could repel positive alpha particles
  • Bohr method proposed that electrons went around in fixed orbits at set distances from the nucleus and the distances were called energy levels
34
Q

describe the process of β– decay

A
  • a neutron changes into a proton and an electron
  • mass number doesn’t change as it has lost a neutron but gained an electron
  • atomic number increases by 1 because it has 1 more proton
35
Q

Describe the process of β+ decay

A
  • proton changes into a neutron and a positron
  • mass number doesn’t change as it has lost a proton but gained a neutron
  • atomic number decreases by 1 because it has one less proton
36
Q

what happens to the atomic and mass number in alpha decay

A
  • mass number decreases by 4 and atomic number decreases by 2
    as alpha decay is when the nucleus emits and alpha particle and it loses two protons and two neutrons
37
Q

what happens to the mass and atomic number in neutron emission

A

mass number decreases by 1 as it has lost a neutron and the atomic number stays the same

38
Q

what happens to the mass and atomic number of gamma rays

A

stays the same

39
Q

what happens to nuclei that have undergone radioactive decay

A

often undergo nuclear rearrangement with a loss of energy as gamma radiation

40
Q

what do nuclear equations do and how to write them

A
  • show radioactive decay by using element symbols
  • written in the form atom before decay -> atom after decay + radiation emitted
  • the total mass and atomic numbers must be equal on both sides
41
Q

Describe how the activity of a radioactive source decreases over
a period of time

A
  • each time a radioactive nucleus decays another radioactive nucleus disappears
  • as the unstable nuclei disappear the activity as a whole will decrease
42
Q

what is the unit of activity of a radioactive isotope

A

Becquerel, Bq

43
Q

what is half-life of a radioactive substance

A

time taken for half the undecayed nuclei to decay or the activity of a source to decay by half

44
Q

Explain that the half-life of a radioactive isotope is the time
taken for half the undecayed nuclei to decay or the activity of a
source to decay by half

A

a short half life = activity falls quickly because the nuclei are very unstable and rapidly decay
a long half life = activity falls more slowly because most of the nuclei don’t decay for a long time so it releases small amounts of radiation for a long time

45
Q

why can it not be predicted when a particular nucleus will decay

A
  • for some isotopes it takes a few hours before all the unstable nuclei have decayed but sometimes it takes millions of years
  • the activity never reaches zero so we have to use half-life to measure how quickly the activity drops off
46
Q

example of half life
- the activity of a radioactive sample is measured as 640 Bq. two hours later it has fallen to 40 Bq, find it’s half-life

A
  1. count how many half-lives it took to fall to 4- Bq
    =initial activity: after 1 half life: after 2 half-lives:
    640 / 2 -> 320 (/2) -> 160 (/2) ->
    after 3 half-lives: after 4 half-lives
    80 (/2) -> 40
  2. calculate the half-life of the sample
    = two hours is four half lives - so half life is 2 hours / 4 = 30 mins
47
Q

how to measure half-life using a graph

A
  • plot activity against time (taking into account for background radiation) it will always be sloped down from y to x ( (but more sloped)
  • half-life is found from the graph by finding the time interval on the bottom axis corresponding to a halving of the activity on the vertical axis
48
Q

Describe the dangers of ionising radiation in terms of tissue
damage and possible mutations

A
  • radiation can enter living cells and ionise atoms and molecules within them which can lead to tissue damage
  • lower doses can cause minor damage without killing cells which can cause mutant cells dividing uncontrollably - cancer
  • higher does can kill cells completely causing radiation sickness if it happens to a lot of cells at once
49
Q

what radiations are the most dangerous outside the body

A

beta and gamma because they can penetrate the body and get to delicate organs

50
Q

what is the most dangerous radiation inside the body

A

alpha particles are the strongest ionising so do all heir damage in a very localised area - contamination not irradiation

51
Q

Explain the precautions taken to ensure the safety of people
exposed to radiation, including limiting the dose for patients and
the risks to medical personnel

A

medical personnel:
- limiting exposure by shielding to protect staff and untreated body parts of patients
- tracers with short half-lives are used
contamination:
- gloves and tongs to stop particles getting stuck to your skin or under your nails
- protective suits to stop breathing in particles
irradiation:
- lead lined boxes
- standing behind barriers or being in different rooms using remote controlled arms
- medical staff may were photographic film badges to monitor their exposure

52
Q

describe irrdiation

A
  • exposure to radiation- objects near a radioactive source are irradiated by it
  • irradiating something doesn’t make it radioactive
53
Q

describe contamination

A
  • radioactive particles getting onto objects
  • these contaminated atoms might decay and release radiation
  • dangerous as radioactive particles could get inside your body
  • once they are contaminated they are at risk of harm until contamination is removed (not always possible) or all radioactive atoms have decayed
54
Q

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A

combined physics (7 decks)

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