Radioactivity (Module 26)

Question 1

How many alpha particles are deflected by more than 90 degrees when they pass through a metal foil?

Answer 1

1 in 10,000

Question 2

Define the inverse square law for gamma radiation.

Answer 2

The intensity of the radiation energy per second passing normally through a unit area. (I = k/r^2)

Question 3

What is the highest source of background radiation in the UK?

Answer 3

Air (such as radon gases)

Question 4

Why should all radioactive material be stored in a lead-lined container?

Answer 4

Because most radioactive sources produce gamma radiation as well, so the container must be thick enough to reduce the gamma emissions as well.

Question 5

Define half-life (And don’t talk about how sexy Gordan Freeman is)

Answer 5

The half-life of a radioactive isotope is the time taken for the mass (number of nuclei) of the isotope to decrease to half the initial mass (number of nuclei)

G-man is watching you, be care Mr.Matthews.

Question 6

Define activity

Answer 6

The activity of a radioactive isotope is the number of nuclei of the isotope that disintegrates per second. (rate of change in the number of nuclei in an isotope)

Question 7

What is the unit of activity?

Answer 7

Becquerel

Question 8

Define decay constant

Answer 8

The probability of an individual nucleus decaying per second.

Question 9

The energy transfer per second from a radioactive source = ___________

Answer 9

A (Activity) x E (energy)

Question 10

How can you prove T 1/2

Answer 10

Ln2/Lambda (0.693/Lambda)

Question 11

What is carbon dating?

Answer 11

• Living plants/trees contain a small percentage of the radioactive isotope of carbon which is formed in the atmosphere as a result of cosmic rays knocking out neutrons from nuclei.
• These neutrons collide with nitrogen nuclei to form carbon 14 nuclei.
• This isotope has a half-life of 5570 years
• neutron + nitrogen nuclei –> Carbon 14 + proton

Question 12

What are the two methods of argon dating?

Answer 12

• Electron capture due to the decay of a radioactive isotope of potassium K into an argon isotope.
• Potassium + electron –> Argon + electron neutrino.
• Beta minus emission through a potassium isotope decay into a calcium isotope (8 times more probable than electron capture)
• Potassium + Beta minus –> Calcium + Antielectron neutrino

Question 13

What should a radioactive tracer have?

Answer 13

• A half-life which is stable enough for the necessary measurement and short enough to decay quickly after use.
• Emit beta or gamma radiation so it can be detected outside the flow path.

Question 14

Define “metastable state”

Answer 14

An excited state of the nuclei of an isotope that lasts long enough after alpha or beta emission for the isotope to be separated from the parent isotope.

Question 15

How and why is a technetium generator prepared?

Answer 15

• Parent nucleus decays after an alpha/beta emission.
• Forms a technetium isotope in an excited state.
• Separates from parents nucleus to be in a metastable state.
• When it de-excites it forms a gamma emission.
• Gamma emissions are therefore used for medical tracers.