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

bacquerel (Bq)

Question 4

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

Answer 4

geiger-muller tube

Question 5

what is count-rate?

Answer 5

the number of radioactive decay per second for a radioactive source.

Question 6

what are the constituents of an alpha particle?

Answer 6

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

Question 6

state four types of nuclear radiation.

Answer 6

1. alpha particles
2. beta particles
3. gamma rays
4. neutrons

Question 7

which type of radiation is most ionising?

Answer 7

alpha radiation.

Question 7

what is the range of an alpha particle through air?

Answer 7

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

Question 7

what will stop ganmma radiation from passing through a point?

Answer 7

• several centimetres of lead
• a few metres of concrete

Question 8

what will stop beta radiation from passing through a point?

Answer 8

• a thin sheet of aluminim
• several metres of air

Question 9

which type of radiation is least ionising?

Answer 9

gamma radiation.

Question 10

state any changes to mass or charge that occur due to the emiision of a gamma ray.

Answer 10

both mass and charge remain unchanged.

Question 11

define the half-life of a radioactive isotope.

Answer 11

• 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 12

describe the nature of radioactive decay.

Answer 12

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

Question 13

what is radioactive contamination?

Answer 13

the presence of unwanted radioactive nuclei on other materials.

Question 14

what is irradiation?

Answer 14

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

Question 15

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

Answer 15

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