Radioactivity: Multiple Choice Questions

Q1. Which of the following best describes the decay constant for a radioisotope?

A

The reciprocal of the half-life of the radioisotope.

B

The rate of decay of the radioisotope.

C

The constant of proportionality which links half-life to the rate of decay of nuclei.

D

The constant of proportionality which links rate of decay to the number of undecayed nuclei.

 

 

Q2. After 64 days the activity of a radioactive nuclide has fallen to one sixteenth of its original value. Calculate the half-life of the radioactive nuclide.

A

2 days.

B

4 days.

C

8 days.

D

16 days.

 

 

Q3. Radioactive decay is described as being spontaneous. In this context spontaneous means:

A
nothing can influence the decay
B
the decay is random
C
the decay can be predicted
D
the decay is exponential

 

Q4. The ionising properties of radiations determine their penetration power.

A
α-particles are not very ionising so they are easily stopped by a thin sheet of paper.
B
α-particles are very ionising so they only travel a few centimetres in air
C
γ-radiation can easily penetrate a sheet of card because it is very ionising
D
γ-radiation is not very penetrating because it is very ionising

 

Q5. Protactinium has a half life of 70s. A sample of protactinium is prepared and monitored over a period of time. Which of the following statements is correct?

A
After 140s the activity will be zero.
B
The activity of the sample will have dropped to 25% of its initial value after 140s.
C
The activity of the sample will have dropped to 12.5% of its initial value after 280s.
D
The activity of the protactinium will never become zero.

 

Q6. Which of the following does not contribute to background radiation?

A
Mobile (or cell) phones
B
Rocks
C
Decaying biological matter
D
Living creatures

 

Q7. A radioactive source is placed 2.0 cm from a detector. The count rate decreases slightly if a sheet of paper is inserted between the source and the detector. It is reduced to background radiation level if the sheet of paper is replaced by a 1.0 cm thick sheet of aluminium.

Deduce what forms of radiation the source emits:

A
Alpha radiation only
B
Alpha and beta radiation.
C
Beta and gamma radiation.
D
Gamma radiation only.

 

Q8. Before carrying out a radioactivity experiment it is necessary to carry out a background radiation count (so that you can calculate the background count rate). The value of that count is not affected by:

A
The location of the experiment.
B
The ambient temperature.
C
The time interval used for the count.
D
The type of detector used.

 

Q9. Within a school laboratory you should always handle radioactive sources with long handled tongs and keep the time of use to a minimum. Choose from the choices below which form of radiation this safety advice most applies to, and for which reason.

Type of Radiation
Reason
A
α-particles
It is the most ionising
B
α-particles
It is the most massive
C
β-particles
It can penetrate up to a metre of air
D
β-particles
It can penetrate the skin and enter the body

 

Q10. Some rocks contain lead as a product of radioactive decay. Via one such decay chain a fixed quantity of polonium decays to a stable isotope of lead.

Which sketch graph best shows the number of lead atoms (N) in the sample as time progresses?