PHY 1020 – Chapter 4: Nuclei and Radioactivity

34 question-and-answer flashcards summarizing key concepts, definitions, and quantitative facts from Chapter 4: Nuclei and Radioactivity.

What causes the sensation we identify as heat?

The molecular and atomic movement and vibrations of matter.

At what temperature (in Kelvin) does all molecular motion theoretically stop?

0 K, absolute zero.

Which three sub-atomic particles make up all atoms?

Protons, neutrons, and electrons.

What uniquely defines an element on the periodic table?

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 common isotopes of hydrogen.

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

Why are many isotopes radioactive?

Because their nuclei are unstable and decay to reach a more stable configuration.

What is nuclear fusion?

The process of two light nuclei combining to form a heavier nucleus, releasing energy.

Where does natural fusion occur on a large scale?

In stars, including our Sun.

Why isn’t Jupiter a fusion reactor like the Sun?

It is not massive enough to reach the pressures and temperatures required for sustained fusion.

Describe alpha decay.

An unstable nucleus emits an alpha particle (2 protons and 2 neutrons), becoming a lighter element.

What particle is emitted during beta-minus decay?

An electron (and an antineutrino), produced when a neutron converts into a proton.

What particle is emitted during beta-plus decay?

A positron (and a neutrino), produced when a proton converts into a neutron.

What are gamma rays?

High-energy photons (electromagnetic radiation) often emitted alongside alpha or beta decay.

Why are gamma rays more dangerous to humans than alpha particles?

They have no mass or charge, allowing them to penetrate deeply and damage internal organs.

What is cosmic radiation?

High-energy charged particles (mostly protons and electrons) from the Sun and other stars that continuously strike Earth.

How long do free neutrons produced in nuclear reactions typically survive?

About 15 minutes before beta-decaying into a proton and electron.

Rank alpha, beta, gamma, and neutron radiation by typical penetration, from least to greatest.

Alpha < Beta < Neutron < Gamma.

What unit equals 0.01 Sievert of radiation dose?

1 rem (or 1000 mrem).

What is the recommended maximum annual radiation exposure for the general public?

5000 mrem or 0.05 Sv (50 mSv).

Approximately how much radiation does an average person receive yearly from natural sources?

About 300 mrem (3 mSv).

Around what acute dose (in rem) can radiation poisoning begin in humans?

About 100 rem (1 Sv).

State the linear hypothesis for radiation-induced cancer.

Cancer risk increases linearly with dose; e.g., 2.5 rem yields an extra 1-in-1000 chance.

How many of the 134 emergency workers at Chernobyl died from acute radiation sickness?

28 workers.

What discrepancy was observed between predicted and actual cancer rates after Hiroshima?

Predicted ~0.8 % extra cancers versus ~2 % observed, suggesting incomplete understanding of radiation effects.

Why does Denver challenge simple radiation-risk models?

Despite higher background radiation (~0.1 rem more 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 two half-lives, what fraction of the original radioactive material remains?

One-quarter (25 %).

What is nuclear fission?

The splitting of a heavy nucleus into two lighter nuclei, releasing energy and neutrons.

What isotope powers most Radioisotope Thermoelectric Generators (RTGs)?

Plutonium-238.

How does a household smoke detector use radioactivity?

An alpha emitter ionizes air; smoke disrupts the ionization, triggering the alarm.

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

5730 years.

Why is radiocarbon dating limited to objects younger than about 60,000 years?

After ~10 half-lives, too little ¹⁴C remains to measure accurately.

Which radioactive isotope is used for dating very old rocks via its decay to ⁴⁰Ca and ⁴⁰Ar?

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