CHEM 120 Week 6 Lab: Nuclear Chemistry

Student Name

Chamberlain University

CHEM-120 Intro to General, Organic & Biological Chemistry

Prof. Name:

Date

Week 6 Lab: Nuclear Chemistry

Learning Objectives

This lab is designed to help students distinguish between chemical and nuclear reactions, understand radioactive decay, and explore the behavior of subatomic particles during nuclear processes. Students will examine alpha, beta, and gamma decay processes and learn to write nuclear equations representing each. Additionally, the lab aims to clarify the concept of half-lives and support students in performing half-life calculations. Applications such as nuclear medicine, radiometric dating (e.g., carbon dating), and nuclear power are explored. The lab also highlights common radioactive decay modes including electron capture, and provides insight into how nuclear binding energy and mass defects reveal stability in atomic nuclei.

Understanding Radioactivity and Atomic Stability

Contrary to the common belief that radioactivity is limited to nuclear power plants, radioactive materials are far more prevalent. In this simulation, students investigate how atomic nuclei behave, which atoms are radioactive, and what causes instability. The interactive holofloor provides a visual representation of proton and neutron interactions, emphasizing why certain isotopic combinations are more stable than others. Alpha, beta, and gamma decay processes each emit different types of radiation and affect nuclear properties in distinct ways.

Atoms produced in stellar cores or nuclear reactors often become unstable isotopes, known as radioisotopes. These nuclei undergo decay, releasing radiation and energy while transforming into more stable elements. This radioactive decay is the focus of experimentation in the virtual simulation.

Part 1: Nuclear Chemistry Lab

Purpose

The goal of this simulation is to explore nuclear reactions by identifying the key subatomic particles and energy changes involved. It allows students to comprehend radioactive decay, analyze half-life behavior, understand nuclear stability, and study real-world applications such as carbon dating and medical imaging with isotopes.

Observations

Particles with identical electrical charges repel each other due to electrostatic forces.
The nuclear force operates only over extremely short distances, functioning solely within the confines of the atomic nucleus.
Half-life concepts enable the estimation of when an unstable atom is likely to undergo decay.

Radiation Effects on Atomic Structure

Radiation Type	Change in Atomic Number	Change in Number of Protons	Change in Mass Number
Alpha Particle	Decreases by 2	Decreases by 2	Decreases by 4
Beta Particle	Increases by 1	Increases by 1	No change
Gamma Particle	No change	No change	No change
Positron Emission	Decreases by 1	Decreases by 1	No change
Electron Capture	Decreases by 1	Decreases by 1	No change

Nuclide Symbols

General Symbol: A X Z
Example: An isotope of strontium has 38 protons and 52 neutrons. The mass number is 90 (38 + 52), and the atomic number is 38. From the periodic table, the element is strontium (Sr), so the nuclide symbol is: ⁹⁰Sr₃₈

Nuclear Equations

Gamma decay of fluorine-19: ¹⁹F → ¹⁹F + γ
Positron emission of sodium-23: ²³Na → ²³Ne + β⁺ (11 → 10)
Electron capture by potassium-41: ⁴¹K + e⁻ → ⁴¹Ar (19 → 18)

Part 2: Half-Life and Medical Applications

Technetium-99m and Half-Life

Technetium-99m, commonly used in diagnostic imaging, has a half-life of approximately six hours. It decays through gamma radiation to form Technetium-99.

a. Percentage remaining after 24 hours: Using the formula A = P(½)^(t/h), where A is the amount remaining, P is the original amount, t is elapsed time, and h is the half-life:

A = X(½)^(24/6) = X/16
(X/16)/X * 100 = 6.25%

Thus, 6.25% of the original amount remains after 24 hours.

b. Why a short half-life is beneficial: Technetium-99m’s short half-life minimizes prolonged radiation exposure, reducing risks such as chest discomfort, dizziness, or heart irregularities. Since it decays rapidly, it exits the body quickly, enhancing patient safety.

Molybdenum-99 as a Precursor

Technetium-99m is derived from the beta decay of Molybdenum-99, which has a longer half-life (2.75 days), making it easier to manage logistically—though current global production is threatened due to facility closures.

a. Nuclear equation for decay: ⁹⁹Mo → ⁹⁹mTc + β⁻

b. Amount remaining after 11 days: Using decay constant λ = 0.693 / 2.75 = 0.252: 11 = (2.303 / 0.252) log(50 / n) Solving for n ≈ 3.12 g

c. Should Mo-99 be stockpiled? No. Due to its relatively short half-life and decay into other elements, stockpiling Molybdenum-99 is ineffective. Continuous production is necessary to ensure a consistent medical supply chain.

Reflection: Iodine-131 in Medical Use

Iodine-131 is a medical isotope primarily used to diagnose and treat thyroid cancer. It is administered orally as a capsule or liquid, easily dissolvable in water or alcohol. Once ingested, it targets the thyroid gland due to the body’s natural iodine absorption process. Iodine-131 undergoes both beta and gamma decay, with a half-life of approximately 8.06 days.

Although effective, safety concerns arise from both external and internal exposure. External contact with large amounts may cause skin or eye burns, while internal accumulation in the thyroid can lead to cancer. If released into the environment, it can be ingested via food, water, or inhalation, causing long-term health issues.

Source:

Centers for Disease Control and Prevention. (2018, April 4). CDC Radiation Emergencies: Iodine. Retrieved October 3, 2022, from https://www.cdc.gov/nceh/radiation/emergencies/isotopes/iodine.htm