Lecture 2 Flashcards
Define activity
A quantified amount of a radioactive substance. It is the number of atomic nuclei that decay per second.
What is a becquerel (Bq)?
The unit of activity. It is the number of atomic transformations per second from a quantity of radioactive material.
How many emissions are there from a cobalt-60 source?
3 separate emissions: 1 beta emission and 2 photon emissions
What is the decay scheme of radium?
- Radium (in rock): alpha decay
- Radon (gas): alpha decay
- Polonium: alpha decay
- Lead: alpha decay
Which elements have the greatest impact on health in the decay scheme of radium-226?
Polonium and lead have the greatest impact of health but radon can also be inhaled and have adverse affects.
What is the non-SI unit for activity?
The Curie (Ci)
What is 1 curie in becquerel and what is the conversion factor?
1 Ci = 3.7 x 10 ¹⁰ Bq
Bq to Ci: ÷ 3.7 x 10 ¹⁰
Ci to Bq: x 3.7 x 10 ¹⁰
The activity of a radionuclide decays at a rate proportional to the _________ of radionuclide present.
Quantity
Define half-life
The time taken for the activity to drop to half of the original activity. Half life is a probabilistic event so each radionuclide is independent of others.
What is the equation for activity in terms of half-life?
A = activity
A₀ = original activity
n = number of radionuclides
t = time
T = half-life
What is the equation for activity (in terms of the decay constant)?
A = activity
A₀ = original activity
λ = decay constant
t = time
What is the equation for half-life (in terms of activity)?
A = activity
A₀ = original activity
λ = decay constant
T = half life
What is the equation for the decay constant (in terms of half-life)?
λ = decay constant
T = half life
0.693 = ln(2)
How can the total activity of a sample be found over a given amount of time?
The activity equation can be integrated over to get a value for total activity.
What is the half-life of radium-226?
1600 years
What is the equation for the effective biological half-life of a sample?
How can the energy dose of a radioactive sample be found?
Multiply the total activity by the energy dose of each transformation of radiation. The total activity should be calculated using the effective biological half-life.
Define specific activity
The amount of activity per gram of a substance.
What is the equation for the number of atoms per gram of a substance?
N = number of atoms per gram
Nₐ = Avogadro’s number = 6.03 x 10²³
A = atomic weight
How can the specific activity be found?
By taking the product of the number of atoms per gram and the decay constant.
What is the equation for specific activity?
SA = specific activity
λ = decay constant
N = number of atoms per gram
Nₐ = Avogadro’s number = 6.03 x 10²³
A = atomic weight
How can the specific activity of an isotope be calculated?
It can be calculated using the specific activity of radium in Bq. The activity of 1g of radium-226 (3.7 x 10¹⁰ Bq) is multiplied by the ratio between the product of the atomic weight and half-life of radium and that of the isotope.
What is the equation for the specific activity of an isotope?
SA = specific activity (isotope)
Aᵣₐ = activity of radium
Aᵢ = activity of isotope
Tᵣₐ = half-life of radium
Tᵢ = half-life of isotope
What are the units for specific activity?
Bq/g
