Lecture 2

Question 1

Define activity

Answer 1

A quantified amount of a radioactive substance. It is the number of atomic nuclei that decay per second.

Question 2

What is a becquerel (Bq)?

Answer 2

The unit of activity. It is the number of atomic transformations per second from a quantity of radioactive material.

Question 3

How many emissions are there from a cobalt-60 source?

Answer 3

3 separate emissions: 1 beta emission and 2 photon emissions

Question 4

What is the decay scheme of radium?

Answer 4

• Radium (in rock): alpha decay
• Radon (gas): alpha decay
• Polonium: alpha decay
• Lead: alpha decay

Question 5

Which elements have the greatest impact on health in the decay scheme of radium-226?

Answer 5

Polonium and lead have the greatest impact of health but radon can also be inhaled and have adverse affects.

Question 6

What is the non-SI unit for activity?

Answer 6

The Curie (Ci)

Question 7

What is 1 curie in becquerel and what is the conversion factor?

Answer 7

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

Question 8

The activity of a radionuclide decays at a rate proportional to the _________ of radionuclide present.

Answer 8

Quantity

Question 9

Define half-life

Answer 9

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.

Question 10

What is the equation for activity in terms of half-life?

Answer 10

A = activity
A₀ = original activity
n = number of radionuclides
t = time
T = half-life

Question 11

What is the equation for activity (in terms of the decay constant)?

Answer 11

A = activity
A₀ = original activity
λ = decay constant
t = time

Question 12

What is the equation for half-life (in terms of activity)?

Answer 12

A = activity
A₀ = original activity
λ = decay constant
T = half life

Question 13

What is the equation for the decay constant (in terms of half-life)?

Answer 13

λ = decay constant
T = half life

0.693 = ln(2)

Question 14

How can the total activity of a sample be found over a given amount of time?

Answer 14

The activity equation can be integrated over to get a value for total activity.

Question 15

What is the half-life of radium-226?

Answer 15

1600 years

Question 16

What is the equation for the effective biological half-life of a sample?

Answer 16

Question 17

How can the energy dose of a radioactive sample be found?

Answer 17

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.

Question 18

Define specific activity

Answer 18

The amount of activity per gram of a substance.

Question 19

What is the equation for the number of atoms per gram of a substance?

Answer 19

N = number of atoms per gram
Nₐ = Avogadro’s number = 6.03 x 10²³
A = atomic weight

Question 20

How can the specific activity be found?

Answer 20

By taking the product of the number of atoms per gram and the decay constant.

Question 21

What is the equation for specific activity?

Answer 21

SA = specific activity
λ = decay constant
N = number of atoms per gram
Nₐ = Avogadro’s number = 6.03 x 10²³
A = atomic weight

Question 22

How can the specific activity of an isotope be calculated?

Answer 22

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.

Question 23

What is the equation for the specific activity of an isotope?

Answer 23

SA = specific activity (isotope)
Aᵣₐ = activity of radium
Aᵢ = activity of isotope
Tᵣₐ = half-life of radium
Tᵢ = half-life of isotope

Question 24

What are the units for specific activity?

Answer 24

Bq/g