P4- Atomic Structure 2

Question 1

Why do unstable nuclei give out radiation ?

Answer 1

• unstable nuclei undergo decay to become more stable
• as they release radiation their stability increases

Question 2

What is the name of the process in which an unstable nucleus gives out radiation to become more stable ?

Answer 2

Radioactive decay

Question 3

Define the activity of an unstable nucleus.

Answer 3

Activity is the rate of decay of a source of unstable nuceli

Question 4

What is the unit of radioactive activity ?

Answer 4

Becquerel (Bq)

Question 5

What is count-rate?

Answer 5

The number of radioactive decays per second for a radioactive source

Question 6

Give an example of a detector that may be used to measure count-rate.

Answer 6

Geiger-Muller tube

Question 7

State four types of nuclear radiation

Answer 7

1. Alpha particles
2. Beta particles
3. Gamma rays
4. Neutrons

Question 8

What are the constituents of an alpha particle?

Answer 8

• two protons and two neutrons
• it is the same as a helium nucleus

Question 9

What is the range of an alpha particle through air ?

Answer 9

A few centimetres ( normally in the range of 2-10cm)

Question 10

What will stop beta radiation from passing through a point ?

Answer 10

• a thin sheet of aluminium
• several metres of air

Question 11

What will stop gamma radiation from passing through a point ?

Answer 11

• several centimetres of lead
• a few metres of concrete

Question 12

Which type of radiation is most ionising ?

Answer 12

Alpha radiation

Question 13

Which type of radiatiom is least ionising ?

Answer 13

Gamma radiation

Question 14

State any changes to mass or charge that occur due to the emission of a gamma ray

Answer 14

Both mass and charge remain unchanged

Question 15

Describe the nature of radioactive decay

Answer 15

• random
• which nuclei decays and when is determined is only by chance
• it is impossible to predict which nuclei will decay and when

Question 16

Define the half-life of a radioactive isotope

Answer 16

• the time it takes for the number of unstable nuclei in a substance to halve

Question 17

What is radioactive contamination?

Answer 17

The presence of unwanted radioactive nuclei on other materials

Question 18

What is irradiation?

Answer 18

• the process of exposing a material to nuclear radiation
• the material does not become radioactive

Question 19

Why is it important for the results of studies on the effects of radiation to be published and shared with other scientists?

Answer 19

• to allow the findings to be independently checked
• this is known as peer review