Radioactivity

Question 1

What is radioactivity?

Answer 1

Radioactivity is the effect where certain rocks containing uranium give out radiation that can penetrate paper and fog photographic film

Question 2

What are the three types of radiation?

Answer 2

The three types of radiation are:

• alpha (a)
• beta (ß)
• gamma (y)

Question 3

The disintegration of nuclei in radioactivity is…

Answer 3

Random and spontaneous

Question 4

What is background radiation?

Answer 4

Background radiation is natural sources of radiation found all around us and inside our bodies

Question 5

Give an examples of background radiation

Answer 5

• radiation reaching Earth from outer space

Question 6

What is ionising radiation?

Answer 6

• the nuclei of some atoms are unstable and emit radiation

- as it passes through matter it causes some atoms to become ions

Question 7

What is the most common type of radiation detector?

Answer 7

The most common type of radiation detector is the Geiger-Müller tube (GM tube) connected to a counter or ratemeter

Question 8

How does a GM tube work?

Answer 8

• when alpha, beta or gamma radiation enters the GM tube it causes some of the argon gas inside to ionise and give an electrical discharge
• this discharge is detected and counted by the counter
• if the counter is connected to its internal speaker, you can hear the click when radiation enters the tube

Question 9

Since they are charged particles, alpha and beta are…

Answer 9

Deflected in magnetic fields

Question 10

Describe beta particle deflection in magnetic fields

Answer 10

Beta particles are deflected more than alpha and in the opposite direction

Question 11

In electric fields:
Alpha is attracted to a…
Beta is attracted to a…

Answer 11

In electric fields:
Alpha is attracted to a negative plate
Beta is attracted to a positive plate

Question 12

Why are gamma rays not deflected in electric or magnetic fields?

Answer 12

Since gamma rays are waves they are not deflected in electric or magnetic fields

Question 13

Explain an industrial use of radiation.

Answer 13

• a gamma source can be used to check welds in metal parts
• it is used in a similar way to X-rays on a human body
• a photographic plate or electronic imaging device is placed behind the weld which is exposed more where the weld is weak

Question 14

Explain how thickness control in manufacturing works (4 marks)

Answer 14

• automatic control of the thickness of paper in paper mills can be obtained by passing beta radiation through the paper and monitoring the count rate
• an isotope with a long half-life is used so that the count rate hardly changes with time
• electrical circuitry is then set up to ensure a constant rate is maintained
• if the rate is too low the rollers automatically move closer to each other making the paper thinner and vice versa

Question 15

What is the unit for radioactivity?

Answer 15

The unit for radioactivity is Bq

1 Bq = 1 disintegration per second

Question 16

A nucleus will hold together if….

Answer 16

It has the right balance of protons and neutrons

Question 17

Which nuclei are radioactive?

Answer 17

All nuclei with atomic numbers greater than 83 are radioactive

Question 18

Radioactive decay is…

Answer 18

Random and spontaneous

Question 19

Give a precaution for using radioactive sources

Answer 19

Keep as far from the source as possible

Question 20

How do you work out the corrected (true) count rate of a radioactive sample?

Answer 20

Corrected count rate = detected count rate from source - background rate

Question 21

Define half-life

Answer 21

The average time taken for half of the nuclei in a sample to decay