PHY 1020 – Chapter 4: Nuclei and Radioactivity

36 question-and-answer flashcards covering key concepts from Chapter 4, including heat, elements, isotopes, fusion, radioactivity, radiation measurement, health effects, half-life, fission, and practical applications such as RTGs, smoke detectors, and radiometric dating.

What physical phenomenon do we perceive as heat?

The molecular and atomic motion and vibrations within matter.

At what temperature does all molecular motion stop?

0 K, known as absolute zero.

How is an element defined in terms of its sub-atomic particles?

By the number of protons in its nucleus.

What is an isotope?

Atoms of the same element that contain different numbers of neutrons.

Name the three isotopes of hydrogen and their mass numbers.

¹H (protium), ²H (deuterium), and ³H (tritium).

Where does fusion naturally occur and what does it primarily convert?

In stars such as the Sun, converting hydrogen into helium.

Why is Jupiter not a natural fusion reactor?

It is not massive enough to reach the pressure and temperature required for sustained fusion.

What happens during alpha decay?

A heavy nucleus ejects a helium nucleus (2 protons and 2 neutrons), becoming a smaller atom.

Which particle is emitted in beta-minus decay?

An electron.

Which particle is emitted in beta-plus decay?

A positron.

What highly penetrating electromagnetic radiation is commonly released during radioactive decay?

Gamma rays (and sometimes x-rays).

Why are gamma rays dangerous to humans?

They have high energy and no mass, allowing them to penetrate deeply and damage internal tissues and DNA.

What is cosmic radiation and where does it originate?

High-energy charged particles (mainly protons and electrons) that come from the Sun and other stars and constantly strike Earth.

Approximately how long can a free neutron exist before it decays?

About 15 minutes.

Which type of radiation can be stopped by a sheet of paper?

Alpha particles.

Which two units are commonly used to measure human radiation dose?

The rem and the sievert (Sv).

Convert 1 rem into sieverts and millirem.

1 rem = 0.01 Sv = 1000 mrem.

What is the recommended maximum yearly radiation exposure for the average person?

About 5000 mrem, or 0.05 Sv (50 mSv).

Around what whole-body dose can radiation sickness begin?

Roughly 100 rem.

Approximately what single dose of radiation is likely lethal to humans?

Around 500 rem if received all at once.

According to the linear hypothesis, how does cancer risk change with radiation dose?

It increases proportionally; about 1 extra cancer case per 1000 people for every 2.5 rem.

How many of the 134 Chernobyl first responders died from acute radiation sickness?

28 individuals.

Why is the Chernobyl explosion often called a “dirty bomb” rather than a nuclear bomb?

It dispersed radioactive material without producing a nuclear explosion.

What puzzling radiation observation is associated with Denver residents?

Despite an extra 0.1 rem per year, Denver’s cancer rate is lower than the U.S. average.

Define half-life.

The time required for half of a radioactive sample to decay.

After three half-lives, what fraction of the original radioactive material remains?

One-eighth (12.5 %).

What nuclear process involves splitting heavy nuclei, often triggered by neutron absorption?

Fission.

Which long-lived isotope starts a decay chain that includes radon-222 and ends at lead-206?

Uranium-238.

What device powers spacecraft like the Mars Rover using heat from radioactive decay?

A Radioisotope Thermoelectric Generator (RTG).

Which isotope is commonly used as fuel in RTGs for space missions?

Plutonium-238.

How does a household smoke detector use radioactivity?

An alpha emitter ionizes air; smoke disrupts the ionization current and triggers the alarm.

What is the half-life of carbon-14 used in radiocarbon dating?

5730 years.

Within what age range is carbon-14 dating reliable?

Roughly 50,000 – 60,000 years.

If a sample’s carbon-14 decay rate falls from 12 to 3 decays per minute, how old is the sample?

About 11,460 years (two half-lives).

Which radioactive isotope of potassium is used in K–Ar dating and what is its half-life?

Potassium-40 with a half-life of 1.248 × 10⁹ years.

In K–Ar dating, what stable isotopes are produced from potassium-40 decay and by which processes?

Calcium-40 via beta-minus decay (89.1 %) and Argon-40 via beta-plus decay (10.9 %).