PHY1020-Ch04

Chapter Overview

• Chapter 4: Nuclei and Radioactivity in PHY 1020

Elements and Atoms

• Heat Definition: Heat arises from molecular and atomistic movement and vibrations, commonly measured in Kelvin (K) or degrees Celsius (C), with absolute zero at 0K indicating no molecular motion.

• Composition of Elements: Elements consist of different atoms made up of protons, neutrons, and electrons.

Elements and Their Isotopes

• Definition of Isotopes: Elements are defined by the number of protons; isotopes vary in neutron count.

  • Example Isotopes of Hydrogen:

    • 1H (Hydrogen-1)

    • 2H (Hydrogen-2)

    • 3H (Hydrogen-3)

• Radioactive Isotopes: Many isotopes are unstable and undergo decay through radioactivity.

Isotope Data: Z=0-28 Part 1

• Critical information on various isotopes, including atomic mass, half-lives, and stability.

  • Ex: Chlorine-17 (Cl) has 17 neutrons, stable isotopes such as Lithium-6 (Li) and Iron-56 (Fe) are listed.

Fusion

• Fusion Process: The combination of two atoms into one, paramount in stars for creating helium and heavier elements.

• Star Example: The sun serves as a natural fusion reactor.

  • Comparison: Jupiter lacks size for significant fusion.

Radioactivity

• Unstable Atoms: Atoms might undergo radioactive decay, releasing radiation to stabilize.

• Alpha Decay: Heavy atoms shed a helium nucleus (alpha particle).

• Beta Decay: A neutron converts to a proton with an electron (beta-minus) or a proton converts to a neutron with a positron (beta-plus).

Radiation Overview

• Ubiquity of Radiation: A natural aspect of life that varies in impact; excessive radiation can be harmful.

• Types of Radiation:

  • Alpha particles, beta particles, gamma rays, and x-rays, which travel differently and have varied dangers.

• Danger of Gamma Rays: Capable of penetrating surfaces and damaging internal organs.

Cosmic Radiation

• Sources: High-energy charged particles from stars, including the sun, affecting Earth constantly.

• Protection: Earth's atmosphere provides shielding from cosmic radiation.

Nuclear Reactions and Neutrons

• Free Neutrons: Produced during nuclear reactions, lasting ~15 minutes before beta decay occurs.

Radiation Penetration Depth

• Types of Radiation and Penetration:

  • Alpha: Stopped by paper

  • Beta: Can penetrate concrete

  • Gamma: Can pass through water

Measuring Radiation

• Units of Measure: Radiation measured in rem or Sieverts.

  • 1 rem = 1000 mrem = 0.01 Sieverts (Sv)

• Exposure Guidelines: Recommended yearly exposure limit is 5000 mrem or 0.05 Sieverts.

• Natural Sources of radiation: Approx. 300 mrem/yr from natural sources, with additional exposure from flights and medical scans.

• Health Risks: Radiation can lead to poisoning at doses around 100 rem; 500 rem in one dose is generally lethal.

Ionizing vs. Non-Ionizing Radiation

• Medical Sources of Ionizing Radiation: Common procedures like X-rays and CT scans.

• Linear Hypothesis: Suggests cancer risk increases with radiation dose exposure, providing conjectures on statistical impacts.

Chernobyl Disaster

• Radiation Doses: High radiation exposure among first responders, leading to acute radiation sickness; considerable public health implications and long-term predictions for cancer risk.

Hiroshima Bombing

• Comparison of Exposures: Quantification of radiation and its predicted health impacts; statistics reveal discrepancies in realities versus hypotheses.

Population Studies in Denver

• Unexpected Findings: Contradictory data showing lower cancer rates despite exposure predictions emphasize gaps in radiation understanding.

Half-Life Concept

• Definition: The time required for half of a radioactive substance to decay; misconception of uniform decay rates highlighted.

• Practical Example: Carbon-14 decay over 5,730 years illustrates half-life implications.

Fission

• Description: The splitting of atoms to release significant energy; key in nuclear reactions.

• Example: Uranium-238 and its decay products provide insight into fission processes.

Applications of Radioactivity

• Radioisotope Thermoelectric Generators (RTG): Utilize heat from radioactivity for energy production, exemplified by space missions (e.g., Mars Rover).

• Smoke Detectors: Operate utilizing alpha emitters to detect smoke-based conductivity changes.

Carbon-14 Dating

• Continuous C-14 Uptake: Understanding of carbon assimilation and decay rates aids dating organic materials.

  • Carbon dating effective for 50,000-60,000 year-old specimens, using decay measurements for age estimation.

Potassium Dating

• Potassium Isotope Variants: The isotopes and decay mechanisms outlined for dating geological and archeological items, particularly long-lived 40K isotope.

Chapter 4 Takeaways

• Key Concepts:

  • Elements and Isotopes

  • Radioactivity and Radiation Dangers

  • Understanding Half-life

  • Practical Applications of Radioactivity