Question 1

A radioactive source has an activity of 1500 Bq. How many unstable nuclei will decay in 3 minutes?

Accepted Answer

$$1500 	imes 180 = 270\ 000$$

Question 2

Which of the following best describes the half-life of a radioactive isotope?

Accepted Answer

The time it takes for the number of nuclei or activity to decrease by half

Question 3

A sample of carbon-14 has a half-life of 5700 years. What fraction of the original sample remains after 17,100 years?

Accepted Answer

$$\frac{1}{8}$$

Question 4

Why is beta radiation used to monitor the thickness of aluminium foil in industry?

Accepted Answer

Beta particles are partially absorbed, allowing changes in thickness to be detected

Question 5

Which type of radiation is most suitable for use in a smoke detector and why?

Accepted Answer

Alpha, because it is strongly ionising and easily absorbed by smoke

Question 6

A radioactive sample has an initial activity of 800 Bq. After 24 hours, the activity is 100 Bq. What is the half-life of the sample?

Accepted Answer

6 hours

Question 7

Which of the following statements about irradiation and contamination is correct?

Accepted Answer

Contamination involves the transfer of radioactive material onto or into an object

Question 8

Why is gamma radiation used to sterilise medical equipment?

Accepted Answer

Gamma rays are highly penetrating and can sterilise equipment without removing packaging

Question 9

Which of the following is the best method to reduce the risk of irradiation when handling a gamma source?

Accepted Answer

Using lead shielding and keeping a safe distance

Question 10

A radioactive isotope has a half-life of 2 days. If you start with 1600 atoms, how many atoms remain undecayed after 6 days?

Accepted Answer

200

Question 11

Which type of radiation is most dangerous if a radioactive source is ingested and why?

Accepted Answer

Alpha, because it is the most ionising inside the body

Question 12

Why is radioactive waste with a long half-life particularly challenging to manage?

Accepted Answer

It must be stored securely for a long time to prevent environmental contamination

Question 13

Which of the following is NOT a recommended safety practice when handling radioactive materials?

Accepted Answer

Handling the source with bare hands

Question 14

A scientist is exposed to a radioactive source with a short half-life. What is the main risk associated with irradiation in this scenario?

Accepted Answer

The source emits a high rate of radiation, increasing the risk of damage

Question 15

Which of the following best explains why gamma rays are used in cancer treatment?

Accepted Answer

Gamma rays are highly penetrating and can reach tumours deep inside the body

Question 16

A radioactive sample has an initial activity of $$A_0. $$Write the equation for the activity $$A$$ after $$n$$ half-lives.

Accepted Answer

$$A = A_0$ 	imes (\frac{1}{2})^n$$

Question 17

Which of the following is a real-world example of contamination?

Accepted Answer

A radioactive isotope is accidentally spilled onto a laboratory bench

Question 18

What is the main reason for using a dosemeter (radiation badge) in workplaces with radioactive materials?

Accepted Answer

To monitor the amount of radiation exposure received by workers

Question 19

Which property of gamma radiation makes it suitable for use as a tracer in medical imaging?

Accepted Answer

It is highly penetrating and can escape the body to be detected

Question 20

A radioactive sample has a half-life of 10 years. If the initial activity is 640 Bq, what will the activity be after 30 years?

Accepted Answer

80 Bq

Radioactivity: Activity, Decay, Uses, and Safety

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