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Half-Life — Reading Comprehension

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MS-PS1-4

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This middle school science reading passage introduces the concept of half-life, aligning with the NGSS MS-PS1-4 standard. Students learn how half-life measures the time it takes for half of a radioactive substance to decay, why this rate is constant for each isotope, and how factors like temperature or pressure do not affect it. The passage illustrates the concept with examples such as carbon-14, uranium-238, and iodine-131, and includes basic calculations and graphs. It also explains the importance of half-life in radioactive dating, which helps scientists determine the age of fossils and artifacts. Glossary terms, Spanish translations, and differentiated versions support diverse learners. Audio integration and graphic organizers enhance student understanding while reinforcing academic vocabulary and scientific thinking.

CONTENT PREVIEW

radioactivity-3 — Half-Life: Understanding Radioactive Decay

Radioactive decay is a natural process that changes one type of atom into another over time. Scientists use the concept of half-life to measure how quickly this change happens. Half-life is the amount of time it takes for half of a radioactive substance to decay into a different element. This predictable rate helps scientists understand everything from the age of ancient fossils to the safety of medical treatments.

How Half-Life Works

Each radioactive isotope has a unique and unchanging half-life. For example, carbon-14 has a half-life of about 5,730 years. That means after 5,730 years, only half of the original carbon-14 atoms remain in a sample; the rest have decayed. After another 5,730 years, only one-quarter of the carbon-14 is left. This process continues until nearly all the atoms have changed. The half-life does not depend on outside factors like temperature or pressure. Instead, it is determined by the structure of the atom's nucleus and the forces inside it.

Examples and Calculations

Other isotopes have very different half-lives. Uranium-238 has a half-life of about 4.5 billion years, making it useful for dating rocks as old as the Earth itself. In contrast, iodine-131 has a half-life of just 8 days, so it is used in medical imaging and treatments where quick decay is needed. Scientists often use graphs to show how much of a radioactive substance remains after each half-life. For example, if you start with 100 grams of iodine-131, after 8 days only 50 grams are left. After 16 days, just 25 grams remain. This pattern follows a mathematical decay curve, which always halves the amount with each interval.

Real-World Applications and Connections

The concept of half-life is crucial for radioactive dating. By measuring how much of a radioactive isotope remains in a rock or fossil, scientists can estimate its age. This helps researchers build timelines for Earth's history and evolution. Half-lives are also important for nuclear power, waste management, and medicine. Understanding half-life allows people to handle radioactive materials safely and predict how long they will remain dangerous or useful. These scientific principles show how the structure of atoms and the forces inside them shape our world, linking chemistry, physics, and earth science.

Half-life is a powerful tool that lets us measure time in ways not possible with clocks or calendars. It helps us unlock ancient secrets, advance technology, and protect our health.

Interesting Fact:
Some radioactive isotopes used in smoke detectors, such as americium-241, have half-lives of over 400 years, making them both useful and long-lasting in safety devices.

What does the term 'half-life' mean?

The time it takes for half of a radioactive substance to decay.The amount of time an isotope remains stable.The time it takes for all atoms to disappear.The lifespan of a living organism.

Which factor does NOT affect the half-life of an isotope?

TemperatureThe structure of the atom's nucleusPressureChemical reactions outside the atom

What is the half-life of carbon-14?

8 days4.5 billion years5,730 years400 years

Why is uranium-238 useful for dating ancient rocks?

It is safe to handle.It has a very short half-life.It has a very long half-life, lasting billions of years.It turns into carbon-14 quickly.

In the passage, which isotope is described as having a half-life of only 8 days?

Carbon-14Uranium-238Iodine-131Americium-241

What is 'radioactive dating' used for?

To find out how old rocks or fossils are.To make new medicines.To change the half-life of isotopes.To increase radioactive decay speed.

Based on the passage, what happens to the amount of a radioactive substance after two half-lives?

One quarter of the original amount remains.All of the substance disappears.The substance becomes more radioactive.It doubles in amount.

True or False: The half-life of an isotope can change if you increase the temperature.

TrueFalse

True or False: After three half-lives, about one-eighth of the original radioactive substance is left.

TrueFalse

Which of the following best describes the importance of understanding half-life in society?

It helps us use radioactive materials safely in medicine, energy, and research.It makes atoms live longer.It lets us change the structure of atoms easily.It is only important for making clocks.