Half Life and Radioactivity

How do atoms with stable nuclei differ from atoms with unstable nuclei?

• Stable nuclei can be found everywhere; unstable nuclei do not occur in nature.

• Stable nuclei emit electrons; unstable nuclei emit protons and neutrons.

• Stable nuclei contain equal numbers of protons and neutrons; unstable nuclei do not.

• The number of particles in stable nuclei never changes; the number of particles in unstable nuclei does change.

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NGSS.HS-PS1-8

A radioactive isotope is a substance that

• will eventually gain electrons through bonding

• will become stable by cooling down

• is unstable and will 'decay' by losing particles

• is not found naturally on the Earth

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NGSS.HS-PS1-8

When Uranium decays it emits an alpha particle, forming an isotope of Thorium. Which of the above decay equations is correct?

• A

• B

• C

• D

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NGSS.HS-PS1-8

In the above decay equation, what are the missing numbers x and y?

• A

• B

• C

• D

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NGSS.HS-PS1-8

The half-life of a substance is

• the amount of substance left after it has decayed

• the time it takes for half of the isotope to decay

• the time it takes for half the mass to have radiated away

• the mass of half of the isotope after decaying

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NGSS.HS-PS1-8

Which of the above graphs shows how the activity of a sample varies with time?

• A

• B

• C

• D

A sample of 16 g of radioactive substance X has a half-life of 2 hours. What percentage of the sample is left after 6 hours?

• none

• 12.5 %

• 25 %

• 33.3 %

What change takes place to an atom during beta decay?

• A proton changes into a neutron

• A proton changes into an electron

• An electron changes into a neutron

• A neutron changes into a proton

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NGSS.HS-PS1-8

The activity of an isotope is

• the number of particles/rays emitted per second

• the same as the half-life in seconds

• the amount of radiation emitted over the lifespan of the isotope

• the amount of heat generated per second

Tags

NGSS.HS-PS1-8

Which of the following half-lives would be most suitable for a medical tracer used in a patient?

• 3 minutes

• 3 hours

• 3 days

• 3 years

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NGSS.HS-PS1-8