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STP 2024 > Radioactivity > Flashcards

Radioactivity Flashcards

Cover lecture material from 1st Uni block

1
Q

What atomic structure model is commonly used for atoms?

A

Bohr Model

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1
Q

What are nucleons?

A

Protons and/or neutrons

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2
Q

What is a nuclide?

A

A specific species of nucleus

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3
Q

How is a nuclide characterised?

A

By no. of protons and neutrons (also nuclear energy state - metastable?)

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4
Q

How does the notation work for nuclides?

A

The atomic mass, atomic number and number of neutrons are all displayed around the atomic number of the nuclide (add image)

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5
Q

What does the shorthand I-131 mean?

A

Iodine 131

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6
Q

How many known isotopes of iodine are there?

A

37

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7
Q

What do all isotopes of iodine have in common?

A
  • All have 53 protons
  • All radioactive apart from I-127
    -All have same chemical properties
    -All have same nuclear properties
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8
Q

What are isobars?

A

Nuclides with the same mass number

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9
Q

What are isotones?

A

Nuclides with the same number of neutrons

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10
Q

What two forces compete in the nucleus of an atom?

A

Nuclear forces (attractive over very short range) and Electrostatic (repulsion over greater distances)

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11
Q

What is needed for a stable nucleus at large numbers of neutrons?

A

Excess neutrons are needed to overcome long-range repulsion between lots of protons.

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12
Q

What does a plot of neutron number against atomic number look like?

A

(add image of line of nuclear stability)

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13
Q

What ratio of N/Z gives stability for small A?

A

1

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14
Q

What ratio of N/Z gives stability for large A?

A

1.5

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15
Q

What are magic numbers?

A

2, 8, 20, 28, 50, 82, 126 - an indication that the nucleus is arranged in energy levels

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16
Q

What is the shell model?

A

The model of an atom arranged in energy levels

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17
Q

What is the ground state?

A

A stable arrangement of nucleons

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18
Q

What is an excited state?

A

A state from which transitions can occur. Unstable and transforms into another state such as a metastable one

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19
Q

What is a metastable state?

A

An unstable state the conversely has a relatively long lifetime before transformation in needed

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20
Q

What is the dividing line for a half life to be considered metastable?

A

10^-9 s

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21
Q

Metastable states are considered to have separate identities and are a classified as nuclei. True or false?

A

True

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22
Q

What is an isomer?

A

Two nuclides that differ due to one being in a metastable state

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23
Q

Give an example of an isomer?

A

Tc99 and Tc99m

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24
Q

What is the definition of radioactive decay?

A

An unstable nucleus transforms into a more stable one by emission of particles (photons or both)

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25
Q

What does the parent radionuclide become after radioactive decay?

A

Daughter radionuclide

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26
Q

What is a decay scheme?

A

A visual representation of radioactive decay

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27
Q

Where in the body is Ra-223 taken up?

A

Because radium mimics calcium in the body, it is taken up in the bones

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28
Q

How is radium used theraputically?

A

Internal radiotherapy treatments

29
Q

What is alpha decay?

A

The emission of a helium nucleus

30
Q

Is alpha decay more typical in light or heavy nuclides?

A

Heavy nuclides

31
Q

Where is alpha decay not used?

A

Imaging

32
Q

What is the range of alpha emissions in air?

A

Approximately 3-5 cm

33
Q

What is the range of alpha emissions in tissue?

A

Less than 100 microns

34
Q

What is beta minus decay?

A

The decay and emission of a proton, electron (beta particle) and anti-neutrino

35
Q

Why does beta decay have a spectrum of energies?

A

The released energy is shared between the beta particle and anti-neutrino

36
Q

What is the mean energy of beta decay?

A

E_mean ≈ (1/3)E_max

37
Q

What can the result of beta decay be?

A

A daughter nucleus in an exited or metastable state often remains

38
Q

Where is beta decay used theraputically?

A

Iodine 131 thyroid therapy

39
Q

Give a less well known example of the use of beta decay?

A

SIRT (selective internal radiation therapy)

40
Q

How does molybdenum 99 decay?

A

Beta decay to Tc99

41
Q

What is isomeric transition?

A

The decay of a metastable nuclide by emission of a gamma ray

42
Q

In diagnostic NM, is it desirable to have no additional particles emitted within the body?

A

Yes

43
Q

What is the difference between X-rays and gamma-rays?

A
  • Originally wavelength determined this
  • Now distinguished by origin:
  • X-rays are from outside the nucleus
  • Gamma rays are from the nucleus
44
Q

Does every transition of Tc99m result in a gamma ray?

A

No

45
Q

What is internal conversion?

A

An alternative to gamma ray emission, energy is transferred to an orbital electrons which is ejected (common in metastable states)

46
Q

Where is internal conversion likely to occur?

A

From an inner shell - the vacancy is then filled by an outer shell electron

47
Q

What is an Auger electron?

A

An electron created in internal conversion when energy is transferred to another orbital electron known as an Auger electron

48
Q

What is electron capture?

A

The absorption of an electron by the nucleus that results in the creation of a neutron and neutrino

49
Q

What is often left after electron conversion?

A

A daughter nucleus that is excited or in a metastable state

50
Q

Characteristic X-rays can have implications for what?

A

Measurement

51
Q

What is a DaTScan?

A

Using the interaction mechanism of electron capture, this scan can be used to investigate Parkinsons and a certain type of dementia

52
Q

What is positron decay?

A

A positron decays into a neutron, electron and neutrino

53
Q

What useful emission is seen in positron decay?

A

The emission of 2 0.511 MeV photons travelling in opposite directions

54
Q

What two processes have the same effect on the nucleus?

A

Electron capture and beta minus decay

55
Q

By what mechanism does F-18 decay?

A

Both electron capture and beta minus (97% beta minus)

56
Q

How does Phosphorus-32 decay?

A

Beta decay - neutron rich

57
Q

How does Oxygen-15 decay?

A

Positron decay - neutron deficient and low Z

58
Q

What decay type is common when there is a neutron excess?

A

Beta decay

59
Q

What decay type is common when there is a Proton excess?

A

Positron or EC

60
Q

What decay type is common when there is a proton and neutron excess?

A

Alpha or fission

61
Q

Why is it important to know about radionuclide production?

A

Helps understand price, availability, purity, etc

62
Q

What are the 3 main mechanisms by which a nucleus can be made unstable to produce useful byproducts?

A
  • Charged particle bombardment (Cyclotron)
  • Neutron activation
  • Fission products
    (The 2nd and 3rd occur in nuclear reactors)
63
Q

What are dees in a cyclotron?

A

A pair of hollow semi-circular electrodes with a gap in between

64
Q

What field is required for a cyclotron to operate?

A

A magnetic field

65
Q

Where are charged particles introduced to a cyclotron?

A

The centre

66
Q

What must be applied to accelerate the charged particles?

A

Voltage

67
Q

There is an electric field inside the dee, true of false?

A

False, there is no electric field

68
Q

How is the voltage used to accelerate the charged particles towards the other dee?

A

By using an alternating voltage

69
Q

What causes the curved path that the charged particles follow?

A

The applied external magnetic field

70
Q

Do we want a high or low energy particle hitting our target?

A

High energy

71
Q
A

STP 2024 (4 decks)

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