Science: Nuclear Physics and Radioactivity
Atomic nuclei, decay, half-life, and radiation safety
Science: Nuclear Physics and Radioactivity
Atomic nuclei, decay, half-life, and radiation safety
Physics - Grade 9-12
- 1
Define the term isotope and explain how isotopes of the same element are different from one another.
Focus on which particle determines the element and which particle can vary.
An isotope is an atom of the same element that has the same number of protons but a different number of neutrons. Isotopes of the same element have the same atomic number but different mass numbers. - 2
Carbon-14 has 6 protons and 8 neutrons. Write its mass number and explain what the number means.
The mass number of carbon-14 is 14. The mass number is the total number of protons and neutrons in the nucleus, so 6 plus 8 equals 14. - 3
Compare alpha, beta, and gamma radiation by describing what each one is and how penetrating it is.
State both the particle or wave type and the relative ability to pass through matter.
Alpha radiation consists of helium nuclei with 2 protons and 2 neutrons and has low penetrating power. Beta radiation consists of fast-moving particles such as electrons or positrons and has medium penetrating power. Gamma radiation is high-energy electromagnetic radiation and has the greatest penetrating power of the three. - 4
During alpha decay, what happens to the atomic number and mass number of the nucleus?
During alpha decay, the atomic number decreases by 2 and the mass number decreases by 4. This happens because the nucleus emits an alpha particle containing 2 protons and 2 neutrons. - 5
A radioactive sample has a half-life of 10 years. If the sample starts with 80 grams, how much will remain after 30 years?
Count how many half-lives fit into 30 years and divide by 2 each time.
After 30 years, 10 grams will remain. Three half-lives pass in 30 years, so the amount changes from 80 grams to 40 grams, then to 20 grams, and then to 10 grams. - 6
Explain why radioactive decay is considered a random process for a single nucleus but predictable for a large sample.
Radioactive decay is random for a single nucleus because it is impossible to know exactly when that nucleus will decay. For a large sample, the overall pattern becomes predictable because many atoms decay according to a stable statistical rate described by the half-life. - 7
If a radioisotope has a half-life of 6 hours, what fraction of the original sample remains after 18 hours? Also state the percent remaining.
Write 18 divided by 6 first, then apply repeated halving.
After 18 hours, 1/8 of the original sample remains, which is 12.5 percent. This is because 18 hours is three half-lives, and the sample is halved three times. - 8
Describe one medical use of radioactivity and explain why it is useful in that application.
One medical use of radioactivity is cancer treatment with radiation therapy. It is useful because carefully targeted radiation can damage or destroy cancer cells while doctors work to limit harm to nearby healthy tissue. - 9
State the law of conservation of charge and mass number as it applies to nuclear equations.
Think about what must add up equally before and after the reaction.
In a nuclear equation, the total mass number must be the same on both sides of the equation, and the total atomic number or charge must also be the same on both sides. This allows missing particles or nuclei to be identified by balancing the equation. - 10
A nucleus emits beta-minus radiation. Describe what happens inside the nucleus during this process.
During beta-minus decay, a neutron in the nucleus changes into a proton and emits an electron. As a result, the atomic number increases by 1 while the mass number stays the same. - 11
List two safety practices used when working with radioactive materials and explain how each one reduces exposure.
Common ideas include time, distance, and shielding.
One safety practice is limiting the time spent near the source, which reduces the total radiation dose received. Another safety practice is using shielding such as lead or concrete, which blocks or reduces the amount of radiation that reaches the body. - 12
A sample begins with 1600 undecayed nuclei. After 4 half-lives, how many undecayed nuclei remain?
After 4 half-lives, 100 undecayed nuclei remain. The sample is halved four times: 1600, 800, 400, 200, and 100.