A sample of a radioactive isotope has a half-life of 20 seconds. If the initial amount of the isotope is 100 grams, how much will be left after 60 seconds?

• A. 6.25 grams
• B. 12.5 grams
• C. 25 grams
• D. 50 grams
• E. 75 grams

The half-life of a radioactive isotope is 30 seconds. What percentage of the original sample remains after 90 seconds?

• A. 12.5%
• B. 25%
• C. 37.5%
• D. 50%
• E. 62.5%

The half life is the (a)   it takes for the amount of radioactive (b)   to halve.

OR

The half life is the ​ (c)   it takes for the radioactive (d)   to halve.

• time
• nuclei
• count rate
• atoms
• length
• alpha
• bequerels
• becquerels

What is the correct unit for radioactivity

• Newtons

• Chernobyls

• Becquerels

• Geigers

If the half life of a radioactive element is 100yrs, how long would it take for the radioactivity to reduce by one half?

• 200yrs

• 100yrs

• 50yrs

• 300yrs

The Half Life of Californium 252 is 5 years.

• TRUE

• FALSE

What is the half-life of iodine-131?

• 32 days
• 8 days
• 16 days
• 24 days

Select all the correct definitions for half life

• The time taken for the number of radioactive nuclei in a sample to reduce by half.

• The time taken for the activity of a sample to reduce by half.

• The activity of a sample after half of it has decayed.

• The number of radioactive nucei after half of them have decayed.

• The time taken for half of each radioactive nuclei to decay.

Tritium is radioactive.

After 36 years, only 10 g of tritium remains from an original sample of 80 g.

Calculate the half-life of tritium.

Give your answer in years.

Give your answer to the nearest 0.1 days.

Give your answer as a number, without units.