P.3.8.1.3 Radioactive decay

Nobelium-259 has a half-life of 3500 s.

What is the decay constant of nobelium-259?

• 8.7 × 10^–5 s^–1

• 2.0 × 10^–4 s^–1

• 1.7 × 10^–2 s^–1

• 1.2 × 10^–2 s^–1

A pure sample of nuclide X containing N nuclei has an activity A. The half-life of X is 6000 years.

A pure sample of nuclide Y containing 3N nuclei has an activity 6A.

What is the half-life of nuclide Y?

• 1000 years

• 3000 years

• 12 000 years

• 18 000 years

Cobalt-60 has a half-life of 5.27 years.

What is the total activity of 1.0 g of cobalt-60?

• 4.2 × 10¹³ Bq

• 2.2 × 10¹⁴ Bq

• 2.5 × 10¹⁵ Bq

• 1.3 × 10²¹ Bq

A radioactive source contains a nuclide which has a half-life of 12 hours. A detector placed near the source records an average count rate of 180 counts per minute. The average background count rate is 20 counts per minute.

What will be the average count rate after 24 hours?

• 40 counts per minute

• 45 counts per minute

• 50 counts per minute

• 60 counts per minute

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

• The reciprocal of the half-life of the radioisotope.

• The rate of decay of the radioisotope.

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

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

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

• 2 days.

• 4 days

• 8 days

• 16 days.

• A

• B

• C

• D

Which of the following does not give a value in seconds?

• capacitance × resistance

• 
• half-life

• 

The actinium series of radioactive decays starts with an isotope of uranium, nucleon (mass) number 235, proton (atomic) number 92.

Which line in the table shows the nucleon number and proton number of the isotope after the emission of 5 α particles and 2 β^– particles?

• A

• B

• C

• D