Nuclear Decay Processes and Half-Life
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Questions and Answers

What happens to the atomic number when an electron fuses with a proton?

  • It decreases by 1. (correct)
  • It increases by 1.
  • It remains unchanged.
  • It becomes zero.
  • Why is the energy spectrum of beta particles not well-defined?

  • The energy is shared randomly between the beta particle and the neutrino. (correct)
  • It consists only of high-energy particles.
  • It only emits alpha radiation during decay.
  • The decay process is always uniform.
  • Which type of radiation results in the highest energy loss from a nucleus?

  • Alpha radiation (correct)
  • Gamma radiation
  • Beta radiation
  • X-ray emission
  • How is the decay constant ($, \lambda$) related to the average lifetime ($\tau$) of a radioactive nucleus?

    <p>$\lambda = 1/\tau$</p> Signup and view all the answers

    What mathematical function describes the time course of radioactive decay?

    <p>Negative exponential function</p> Signup and view all the answers

    At which point in the decay curve is the number of undecayed nuclei equal to approximately 37% of the initial value?

    <p>At $,N_0/e$</p> Signup and view all the answers

    What is represented by the variable $T_{1/2}$ in the decay formula?

    <p>Half-life of the radioactive nuclei</p> Signup and view all the answers

    What type of particle is emitted alongside a beta particle in beta decay?

    <p>Neutrino or antineutrino</p> Signup and view all the answers

    What is the remaining fraction of undecayed nuclei after a time period equal to three times the half-life?

    <p>One-eighth</p> Signup and view all the answers

    What method is suggested for accurately determining the average lifetime from a decay graph?

    <p>Use of semi-logarithmic coordinates</p> Signup and view all the answers

    What does the effective decay constant ( abla_eff) represent?

    <p>The combined rate of physical and biological decay</p> Signup and view all the answers

    Why is determining the effective half-life significant in the context of radioactive pharmacons?

    <p>It is the shortest out of the physical, biological, and effective half-lives.</p> Signup and view all the answers

    What does the slope of the semi-logarithmic plot represent in the decay analysis?

    <p>The decay constant ( abla)</p> Signup and view all the answers

    What are two primary ways the amount of radioactive nuclei can decrease in a patient's body?

    <p>Physical decay and biological decay</p> Signup and view all the answers

    How do you determine the slope from the plotted graph of ln(N) vs elapsed time?

    <p>Using the triangle method to calculate change</p> Signup and view all the answers

    What is the relationship between effective decay, biological decay, and physical decay?

    <p>Effective decay constant is the sum of both biological and physical decay constants.</p> Signup and view all the answers

    What effect does the asymmetrical distribution of nucleons have on binding energy?

    <p>It decreases binding energy due to differing energy states of neutrons and protons.</p> Signup and view all the answers

    In the shell model, what prohibits neutrons from occupying proton energy states?

    <p>Pauli’s exclusion principle.</p> Signup and view all the answers

    What is indicated by the presence of magic numbers in nuclei?

    <p>Nuclei with magic numbers exhibit greater stability.</p> Signup and view all the answers

    For light nuclei, what ratio of neutrons to protons (N/Z) is considered optimal for stability?

    <p>N/Z = 1.</p> Signup and view all the answers

    What primary limitation does the shell model for nuclei exhibit?

    <p>It fails to explain all phenomena observed in nuclei.</p> Signup and view all the answers

    What is the configuration of nucleons in the 1s shell according to the model?

    <p>2 protons and 2 neutrons.</p> Signup and view all the answers

    Which features are similar between atomic and nuclear shells?

    <p>Both show discrete energy levels.</p> Signup and view all the answers

    What happens to binding energy as the number of neutrons in a nucleus becomes disproportionately higher than protons?

    <p>Binding energy decreases.</p> Signup and view all the answers

    What type of decay occurs in the parent element of a radioactive decay series?

    <p>Alpha decay</p> Signup and view all the answers

    What is the formula to determine the mass number of members in a radioactive series?

    <p>A = 4n + C</p> Signup and view all the answers

    What do you get when you fix the neutron number and move parallel to the Z axis?

    <p>Isotones</p> Signup and view all the answers

    Which of the following isotopes is radioactive and ejects beta negative particles?

    <p>Tritium</p> Signup and view all the answers

    What is the nucleon mass number (A) composed of in a nucleus?

    <p>Protons and neutrons</p> Signup and view all the answers

    Which isotope of carbon is commonly used in carbon dating due to its half-life?

    <p>Carbon-14</p> Signup and view all the answers

    What does the mass number (A) represent in the context of the nucleus?

    <p>The sum of protons and neutrons</p> Signup and view all the answers

    How can the stability of nuclei be determined?

    <p>By analyzing the Z and N values on a graph</p> Signup and view all the answers

    How does the addition of an extra neutron affect the stability of a nucleus?

    <p>It increases binding energy and stability.</p> Signup and view all the answers

    Which region in the N-Z graph represents stable nuclei?

    <p>The green band above the 1:1 ratio line.</p> Signup and view all the answers

    What process occurs in unstable nuclei with an N/Z ratio much higher than 1?

    <p>Neutrons are transformed into protons via beta decay.</p> Signup and view all the answers

    What is indicated by the blue strip in the N-Z graph?

    <p>Nuclei that are close to stability but may undergo beta plus decay.</p> Signup and view all the answers

    In terms of nuclear stability, what does the hatched elliptical area represent?

    <p>Unstable, heavy nuclei that can undergo alpha decay.</p> Signup and view all the answers

    Which term in the semiempirical model accounts for the decrease in binding energy due to surface nucleons?

    <p>Surface energy term.</p> Signup and view all the answers

    What is a significant aspect of the Weizsäcker formula for binding energy?

    <p>It is based on the principles of incompressible matter.</p> Signup and view all the answers

    Why are light nuclei unable to emit alpha particles?

    <p>Alpha decay is not energetically favorable.</p> Signup and view all the answers

    Study Notes

    Nuclear Decay Processes

    • Electron capture:
      • Electron fuses with a proton in the nucleus, transforming it into a neutron.
      • Atomic number decreases by one, mass number remains unchanged.
      • Characteristic X-rays or Auger electrons are emitted.
    • Energy quantization:
      • Electrons in atoms absorb or emit energy in discrete portions (quanta).
      • Energy levels of a bound electron are quantized.
      • Energy of radioactive decays is characteristic for the parent nucleus, used for identification.
      • Alpha decay has the highest energy loss, followed by beta and then gamma.
      • Alpha and gamma decay energies are quantized and specific to the emitting nucleus.
      • Beta decay energy is quantized, but its spectrum is continuous due to random energy distribution between beta particle and neutrino/antineutrino.

    Radioactive Decay and Half-Life

    • Radioactive decay:
      • Number of parent nuclei decreases over time, following a negative exponential function.
      • N(t) = N0 * e^(-λt) = N0 * e^(-t/τ), where:
        • N(t) is the number of undecayed nuclei at time t.
        • N0 is the initial number of nuclei.
        • λ is the decay constant (rate constant).
        • τ is the average lifetime of the nuclei.
    • Half-life:
      • Time taken for half of the radioactive nuclei to decay.
      • N(t) = N0 * 2^(-t/T½), where T½ is the half-life.
    • Graphical analysis:
      • Semi-logarithmic plot (ln(N/N0) vs time) linearizes the exponential decay function, allowing for easier determination of the decay constant.
      • Slope of the line equals -λ.

    Effective Decay

    • Radioactive pharmacons in living organisms undergo both physical and biological decay.
    • Physical decay: Radioactive nucleus decays into a daughter nucleus, emitting β or γ rays.
    • Biological decay: Radiopharmacon is removed from the body through excretion or exhalation.
    • Effective decay: Combined effect of physical and biological decay.
    • Effective decay constant (λeff): Sum of physical (λphys) and biological (λbiol) decay constants.
    • Effective half-life: Lowest out of the three half-lives (physical, biological, and effective).

    Radioactive Decay Chains/Series

    • Naturally occurring radioactive elements are categorized into three decay chains.
    • Parent element decays via alpha emission.
    • Subsequent daughter elements can decay via alpha or beta emission.
    • Mass number of each member follows the formula: A = 4n + C, where C = 0, 1, 2, or 3.

    Nuclear Structure and Stability

    • Nucleus: Contains positively charged protons (Z) and neutral neutrons (N).
    • Nucleon/mass number (A): Sum of protons and neutrons.
    • Isotopes: Atoms of the same element with different neutron numbers.
    • Isotones: Atoms with the same neutron number (N).
    • Isobars: Atoms with the same mass number (A).
    • Nuclear stability:
      • Green band in N-Z graph represents stable nuclei.
      • Red band represents nuclei with excess neutrons (N/Z ratio much higher than 1), leading to β- decay and neutron transformation into a proton for stability.
      • Blue strip represents nuclei with a N/Z ratio close to 1 (too many protons), leading to β+ decay and proton transformation into a neutron for stability.
      • Hatched elliptical area represents heavy nuclei undergoing α decay or fission.
      • Light nuclei are unable to emit α particles due to energetic constraints.

    Semiempirical Model of Nuclear Binding Energy

    • Model treats nucleus as an incompressible droplet.
    • Weizsäcker formula calculates the binding energy based on:
      • Volumetric term: Proportional to A, represents nuclear force contribution.
      • Surface term: Accounts for decreased binding energy at the surface of the nucleus.
      • Coulomb term: Represents the electrostatic repulsion between protons.
      • Symmetry term: Accounts for the difference in energy levels between protons and neutrons due to asymmetric nucleon distribution.

    Nuclear Shell Model

    • Assumes that nucleons occupy discrete energy levels within the nucleus.
    • Elements with "magic numbers" of protons or neutrons have many stable isotopes and are very stable.
    • Based on independent shell systems for protons and neutrons.
    • Predicts shells analogous to electron shells (1s, 1p, 2s, 1d, etc.).
    • Limitations: Works better for lighter nuclei and doesn't accurately predict magic numbers for heavier nuclei.
    • Neutron vs. proton shells remain separate.

    Stability of Nuclei

    • Even Z and N generally result in stable nuclei.
    • N/Z ratio ≈ 1 is crucial for stability in light nuclei.
    • N/Z ratio > 1 is important for stability in heavy nuclei.

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    Description

    This quiz examines the processes of nuclear decay, focusing on electron capture and energy quantization. It also delves into radioactive decay and the concept of half-life, covering how parent nuclei decrease over time. Test your understanding of these fundamental concepts in nuclear physics.

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