4.2 ATOMS AND NUCLEAR RADIATION

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 nuclei.

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 radiation 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 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
● The time it takes for the count rate
from a sample to fall to half its initial
level

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