Half life practice problems

What is Half-life?

• The amount of time it takes for some of the nuclei in a sample of the isotope to decay
• The amount of time it takes for half the electrons in a sample of the isotope to decay
• The amount of time it takes for half the nuclei in a sample of the isotope to decay
• the amount of time it takes to double the nuclei in a sample of the isotope to decay

The half-life of Zn-71 is 2.4 minutes. If one had 100.0 g at the beginning, how many grams would be left after 7.2 minutes has elapsed?

• 100.0g
• 50.0g
• 12.5g
• 8.5g

After the third half-life, how much of the sample is left?

• 1/2
• 1/3
• 1/16
• 1/8

The half life of iodine-131 is 8 days. What fraction of an iodine-131 sample will remain after 40 days?

• 1/2
• 1/64
• 1/5
• 1/32

Barium-122 has a half-life of 2 minutes. A fresh sample weighing 80 g was obtained. If it takes 10 minutes to set up an experiment using barium-122, how much barium-122 will be left when the experiment begins?

• 0.25g
• 2.5g
• 25g
• 80g

The half-life of strontium-90 is 25 years. How much strontium-90 will remain after 100 years if the initial amount is 4.0 g?

• 3.0g
• 0.25mg
• 0.3g
• 0.25g

How many protons does U 235 atom have ?

• 235
• 92
• 143
• 67

The radiation detected from a piece of rock is reduced significantly when the rock is wrapped in foil. What type of radiation is being emitted?

• Alpha
• Beta
• Gamma
• none of the above

The beta particle has a charge of ...........

• +1
• -1
• -2
• +4

Uranium-238  decays into  Thorium-234  by emitting .........

• an alpha particle
• a beta particle
• gamma rays
• visible light