Radioisotopes

Question 1

What is an atom composed of?

Answer 1

Protons: element

Neutrons: isotope

electrons

Question 2

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

Answer 2

more neutrons are needed to stabilise it

Question 3

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

Answer 3

Beta- emitters: too many neutrons

Beta+ emitters: too many protons

Alpah emitters: isotope too heavy and needs to loose mass

Gamma emitters: nuclei excited

Question 4

What are alpha emitters and give an example of one?

Tell me the key features of alpha emitters?

Answer 4

• 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⁺

Question 5

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

Answer 5

• 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

Question 6

Tell me about gamma emitters and their key features?

Answer 6

• 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

Question 7

When will nuclei stop decaying?

Answer 7

When a stable isotope is formed

Question 8

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

Answer 8

Question 9

Write the rate of decay equation is respect to Kt ?

Answer 9

Question 10

What is the half life equation?

Answer 10

Question 11

What equation did the half life equation (t_1/2) come from?

Answer 11

Question 12

How can we determine the rate of decay?

Answer 12

by counting the number of decays per secnd (dps)

Question 13

what’s the relationship between

Bq (Becquerel) and dps?

Answer 13

1 Bq = 1dps

Question 14

What does 1 Ci (curie) equal in dps?

Answer 14

1 Ci = 3.7x10¹⁰ dps

Question 15

What can be used to measure radioactivity?

Answer 15

1. ionising detector
2. scintillation detector

Question 16

How does an ionising detector work?

Answer 16

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

Question 17

What are the pros and cons to a ionising detector?

Answer 17

Pros

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

Cons

• not easy to apply to liquid samples

Question 18

How does a liquid scintillation counter work?

Answer 18

• 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

Question 19

What the effects of particle energy on scintillation detection?

Answer 19

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

Question 20

Whats the equation for the counting efficiency?

Answer 20

Counting efficiency= CPM / DPM

CPM= counts per minute

DPM= decays per minute

Question 21

Whats the equation for DPM?

Answer 21

DPM = CPM / counting efficiency

Question 22

What effects counting efficiency?

Name and explain the different types of this?

Answer 22

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)

Question 23

What are the uses of measuring radioacitivity in biology?

Answer 23

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

Question 24

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

Answer 24

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

Question 25

Read about PET scans

Question 26

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

Answer 26

• sensitivity
• chemically identical

Question 27

What are the alternatives to using radioactive isotopes?

Answer 27

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

Question 28

What does 1 Ci equal in dpm?

Answer 28

1 Ci = 3.7x10¹⁰ dps = 2.22x10¹² dpm