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CHEM1039 > Radioisotopes > Flashcards

Radioisotopes Flashcards

1
Q

What is an atom composed of?

A

Protons: element

Neutrons: isotope

electrons

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2
Q

As the atomic number of an atom increases, what’s needed in order to stabilise it?

A

more neutrons are needed to stabilise it

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3
Q

What are the types of emitters that contribute to nuclei decay and what causes these emitters to be released?

A

Beta- emitters: too many neutrons

Beta+ emitters: too many protons

Alpah emitters: isotope too heavy and needs to loose mass

Gamma emitters: nuclei excited

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4
Q

What are alpha emitters and give an example of one?

Tell me the key features of alpha emitters?

A
  • alpha particle
  • He2+
  • occurs in heavy element such as 238U and 210P
  • Highly ionising
  • Low penetrating power (due to its mass): few cm of air/ outer layer of skin
  • Energy ≈ 5 MeV (mega electron volts)

210Po –> 206Pb + He2+

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5
Q

Tell me about beta emitters and their key features and an example of a beta emitter?

A
  • beta particle

High enegry electrons emitted from nucleus

Accompaned by emission of anti-neutrino

  • occurs in nuclei with too many neutrons

mass remains the same

element changes (atomic number increases by +1)

  • medium penetrating power
  • energy: varies, typically < 3 meV
  • e.g. Carbond -14

14C –> 14N + 0e + 0V

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6
Q

Tell me about gamma emitters and their key features?

A
  • Gamma radiation with high frequency photons
  • occur in nuclei in excited state

frequenctly follow alpha or beta decay

  • high penetrating power

Lead shiled wont completely stop

  • Energy varies: 10’s to 1000’s KeV (kiloelectron volts)
  • no change in isotope number of mass
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7
Q

When will nuclei stop decaying?

A

When a stable isotope is formed

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8
Q

The rate of decay is proportional to concentration of material. What equation described this?

A
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9
Q

Write the rate of decay equation is respect to Kt ?

A
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10
Q

What is the half life equation?

A
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11
Q

What equation did the half life equation (t1/2) come from?

A
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12
Q

How can we determine the rate of decay?

A

by counting the number of decays per secnd (dps)

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13
Q

what’s the relationship between

Bq (Becquerel) and dps?

A

1 Bq = 1dps

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14
Q

What does 1 Ci (curie) equal in dps?

A

1 Ci = 3.7x1010 dps

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15
Q

What can be used to measure radioactivity?

A
  1. ionising detector
  2. scintillation detector
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16
Q

How does an ionising detector work?

A
  • ionising radiation interacts with inert gas
  • which causes the release of an electron and ion
  • these migrate to an electrode and generate a current
17
Q

What are the pros and cons to a ionising detector?

A

Pros

  • Can detect most types of radiation
  • cascade can amplify signal (Gieger muller tube)

Cons

  • not easy to apply to liquid samples
18
Q

How does a liquid scintillation counter work?

A
  • samples to be counted are prepared by adding scintillation fluid (cocktail) to the beta emitter
  • as beta particles are released and interact with the fluid, photons of light are produced and measured
  • the intensity of light is proportional to the energy of the beta particle; therefore the spectra for different energy beta emitters are unique
19
Q

What the effects of particle energy on scintillation detection?

A
  • the size of response is proportional to the energy of particle
  • enable simultaneous detection of different isotopes
20
Q

Whats the equation for the counting efficiency?

A

Counting efficiency= CPM / DPM

CPM= counts per minute

DPM= decays per minute

21
Q

Whats the equation for DPM?

A

DPM = CPM / counting efficiency

22
Q

What effects counting efficiency?

Name and explain the different types of this?

A

Quenching

1. Chemical quenching

  • agents in cocktail interfere with transfer from solvent to fluorophore

2. Colour quenching

  • agents in cocktail absorb light in region in which fluorophore emits

3. Self-absorption

  • particle does not enter cocktail- particular acute for weak beta-emitter (3H)
23
Q

What are the uses of measuring radioacitivity in biology?

A
  1. Tracers in metabolic pathways
  2. imaging
  3. binding/ transport assay
24
Q

Tell me about imaging (scintigraphy. single-photo emission computerised tomography)

A
  • gamma emitting radio-nucleotides ingested
  • emission detected using solid-state gamma cameras
  • 3D image can be built up by rotating detector around the patient
25
Q

Read about PET scans

26
Q

There are risks associated with radioactive isotopes, but why do we still use them?

A
  • sensitivity
  • chemically identical
27
Q

What are the alternatives to using radioactive isotopes?

A
  • Spectroscopic methods becoming more sensitive (fluoroescence assays)
  • Non-radioactive isotopes can be used to follow expression/ metabolic pathways (MS/NMR)
28
Q

What does 1 Ci equal in dpm?

A

1 Ci = 3.7x1010 dps = 2.22x1012 dpm

CHEM1039 (11 decks)

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