Topic 4 - Atomic structure

Question 1

What is the definition of radioactive decay? What is the definition of activity? What is count rate?

Answer 1

Radioactive decay:
— When unstable isotopes randomly give out radiation as they decay in order to become more stable.

Activity:
— The rate at which a source of unstable nuclei decays. It is measured in Becquerels (Bq).

Count rate:
— Number of decays recorded each second by a detector.

Question 2

Describe alpha, beta and gamma radiation.

Answer 2

Alpha radiation:

• – Alpha particle emitted which consists of two protons and two neutrons (like helium atom)
• – Low penetration
• – Travel few cm in air, absorbed by paper
• – Strongly ionising

Beta radiation:

• – High speed electron released by nucleus (for every electron emitted, a neutron in the nucleus turns into a proton)
• – Moderate penetration
• – Travel few metres in air, absorbed by aluminium
• – Moderately ionising

Gamma radiation:

• – Gamma rays (electromagnetic radiation)
• – High penetration
• – Travels long distance in air, absorbed by thick sheets of lead or concrete wall
• – Weakly ionising

Question 3

What are the symbols of an alpha and beta particle?

Answer 3

Alpha:
4
He
2

Beta:
0
e
-1

Question 4

What is the definition of half - life?

Answer 4

Half-life:

— The time taken for a number of radioactive nuclei of an isotope in a sample to halve.

Question 5

Explain the difference between radioactive contamination and irradiation.

Answer 5

Radioactive contamination:
— The presence of unwanted materials containing radioactive atoms on another material. Contamination could then cause further harm by the radioactive atoms decaying which will release radiation which could potentially enter the body.

Irradiation:
— Exposing an object to nuclear radiation via a radioactive source but the object itself does not become radioactive