Radioactivity

A reading is taken every 10 minutes of the number of emissions per second from a radioactive source. The table shows the readings. What is the half-life of the source?

• 10 min

• 20 min

• 40 min

• 60 min

The graph shows how the decay rate of a radioactive source changes with time. What will be the activity at 8 days?

• 0 decays/ s

• 125 decays/ s

• 250 decays/ s

• 500 decays/ s

A sample of a radioactive isotope has an initial rate of emission of 128 counts per minute and a half-life of 4 days. How long will it take for the rate of emission to fall to 32 counts per minute?

• 2 days

• 4 days

• 8 days

• 12 days

A scientist carries out an experiment using a sealed source which emits β-particles. The range of the β-particles in the air is about 30cm. Which precaution is the most effective to protect the scientist from the radiation?

• handling the source with long tongs

• keeping the temperature of the source low

• opening all windows in the laboratory

• washing his hands before leaving the laboratory

A powder contains 400mg of a radioactive isotope that emits α-particles. The half-life of the isotope is 5 days. What mass of this isotope remains after 10 days?

• 0 mg

• 40 mg

• 100 mg

• 200 mg

In a laboratory, a detector of ionising radiation records an average background count rate of 8 counts per second. A radioactive source is now placed close to the detector. The count rate on the detector rises to 200 counts per second. What is the count rate due to radiation from the radioactive source?

• 25 counts/ s

• 192 counts/ s

• 200 counts/ s

• 208 counts/ s

A radioactive source produces a count rate on a detector of 1600 counts / s. After 32 hours the count rate has fallen to 100 counts / s. Both count rates have been corrected for background radiation. What is the half-life of the source?

• 2 hours

• 6.4 hours

• 8 hours

• 16 hours

A radioactive isotope is placed near a detector. The readings on the detector are corrected for background radiation and recorded every hour. The table shows the corrected readings. What is the half-life of the isotope?

• between 0 and 1 hour

• between 1 hour and 2 hours

• between 2 hours and 3 hours

• between 3 hours and 4 hours

A radioactive substance has a half-life of 2 weeks. At the beginning of an investigation, a sample of the substance emits 3000 β-particles per minute. How many β-particles will it emit per minute after 6 weeks?

• 0

• 375

• 500

• 1500

The table shows the results of an experiment to find the half-life of a radioactive substance. What is the half-life of the substance?

• 60 seconds

• 120 seconds

• 180 seconds

• 240 seconds