الجزئية الي لازم حفظ وتركيز CH2
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Questions and Answers

What is the primary cause of spontaneous fission in heavy nuclei?

  • Maximum nuclear binding energy at low atomic mass
  • Reduction of atomic mass number below 58
  • High neutron-to-proton ratio
  • Maximum nuclear binding energy at high atomic mass (correct)

    • What is emitted during alpha decay?

  • Gamma rays
  • Helium ions (correct)
  • Neutrons
  • Protons

    • Which of the following nuclides is most prone to alpha decay?

  • Iron-56
  • Carbon-14
  • Cobalt-60
  • Uranium-238 (correct)

    • What happens to the atomic number after an atom undergoes alpha decay?

    <p>It decreases by 2</p> Signup and view all the answers

    Which decay mode involves the emission of positrons?

    <p>Beta decay (β+)</p> Signup and view all the answers

    What is the range of alpha particles in matter?

    <p>Very short range, only a few millimeters</p> Signup and view all the answers

    In beta decay (β-), what is the problem that atoms are addressing?

    <p>Too many neutrons and too few protons</p> Signup and view all the answers

    Which of the following decay modes has the least probability of occurrence in uranium-238?

    <p>Spontaneous fission</p> Signup and view all the answers

    What is the result of beta emission on atomic number and atomic mass number?

    <p>Increases atomic number by 1, mass number remains the same</p> Signup and view all the answers

    What particle is emitted during positron decay?

    <p>Beta particle</p> Signup and view all the answers

    What happens during electron capture?

    <p>An electron is captured by a proton to form a neutron</p> Signup and view all the answers

    What is the relationship between excitation energy and the decay process for proton-rich radionuclides?

    <p>Higher excitation energy increases probability of positron decay</p> Signup and view all the answers

    What carries the remaining energy not carried by the beta particle during beta emission?

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

    What condition must be met for positron decay to occur?

    <p>Energy difference greater than 1.02 MeV</p> Signup and view all the answers

    What are annihilation radiations produced during positron decay?

    <p>Two photons of 511 keV</p> Signup and view all the answers

    When does electron capture predominantly occur?

    <p>When excitation energy is less than 1.02 MeV</p> Signup and view all the answers

    What is the process of a radioactive nucleus losing energy called?

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

    Which equation represents the radioactive decay relationship?

    <p>$A = A_o e^{-λt}$</p> Signup and view all the answers

    What is half-life (T1/2) defined as?

    <p>The time needed for all radioactive nuclei to decay to half activity</p> Signup and view all the answers

    What is the correct formula for calculating the effective half-life (Te)?

    <p>$1/T_e = 1/T_p + 1/T_b$</p> Signup and view all the answers

    How is the average lifetime (Ƭ) of radioactive atoms calculated?

    <p>Ƭ = 1/λ</p> Signup and view all the answers

    What unit is equivalent to 1 disintegration per second?

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

    What do the decay constant (λ) and half-life (T1/2) relate to each other as?

    <p>λ = 0.693 / T_{1/2}</p> Signup and view all the answers

    What is the significance of the half-value layer in radiologic science?

    <p>It correlates with the concept of half-life</p> Signup and view all the answers

    Study Notes

    Radioactivity

    • Radionuclides are unstable and decay by emitting particles or gamma radiation to achieve a stable configuration of protons and neutrons in the nucleus.
    • Radionuclides can decay through several modes:
      • Spontaneous fission (SF)
      • Isomeric transition (IT)
      • Alpha decay
      • Beta decay (β-)
      • Positron decay (β+)
      • Electron capture (EC) decay

    Spontaneous Fission (SF)

    • Fission is a process where a heavy nucleus breaks into two fragments, accompanied by the emission of two or three neutrons.
    • The nuclear binding energy of elements reaches a maximum at an atomic mass number of approximately 58.
    • Spontaneous breakdown into smaller nuclei and a few isolated nuclear particles becomes possible at higher atomic mass numbers.

    Alpha Decay (α)

    • Alpha decay primarily occurs in heavy nuclides like uranium and radon.
    • Alpha particles are helium ions with two protons and two neutrons.
    • After alpha decay, the atomic number is reduced by 2 and the mass number by 4.
    • Example: 222Rn86 → 218Po84 + α
    • Alpha particle energy ranges from 1 to 10 MeV.
    • Alpha particles have a very short range in matter.

    Beta Decay (β−)

    • Atoms undergo radioactivity to achieve stability.
    • Atoms with too many neutrons and not enough protons can stabilize by lowering the number of neutrons and increasing the number of protons.
    • A neutron is converted into a proton, an electron (β−), and an antineutrino (ν).
    • Example: n → p + β− + ν
    • Beta emission increases the atomic number by one (Z → Z + 1), while the atomic mass number remains the same.
    • This nuclear transformation changes an atom from one element to another.
    • Example: 131I53 → 131Xe54 + β−

    Positron Decay (β+)

    • When a radionuclide is proton-rich, a proton converts to a neutron, emitting a positron (β+) and a neutrino (ν).
    • The atomic number decreases by 1 (Z → Z – 1).
    • Example: p → n + β+ + ν
    • Positron decay only occurs when the energy difference between the parent and daughter nuclides is greater than 1.02 MeV.
    • Positrons lose energy while passing through matter.
    • When losing almost all their energy, positrons combine with an atomic electron, and annihilation occurs, resulting in two photons of 511 keV each. These are called annihilation radiations.

    Electron Capture (EC)

    • Electron capture is an alternative to β+ decay for proton-rich radionuclides.
    • An electron from an inner electron shell (particularly the K shell) is captured by a proton in the nucleus, forming a neutron and a neutrino.
    • Example: p + e− → n + ν
    • Electron capture lowers the atomic number of the daughter nuclide by 1 (Z → Z – 1).
    • Electron capture usually occurs in nuclides with excitation energies less than 1.02 MeV.

    Radioactivity

    • Radioactivity (nuclear decay) is the process by which an unstable atomic nucleus loses energy by emitting radiation (e.g., alpha particles, beta particles, gamma rays).
    • A material containing unstable nuclei is considered radioactive.

    Radioactive Decay Laws

    • A = A₀ * e^(-λt), where:
      • A = activity after time t
      • A₀ = initial activity
      • λ = decay constant
      • t = time
    • Activity is also A = λN, where N is the number of radioactive atoms.

    Half-life (T½)

    • The half-life is the time needed for half of the radioactive nuclei to decay.
    • T½ = 0.693/λ

    Average (Mean) Lifetime (T)

    • The average time required for all radioactive atoms to decay.
    • T = 1/λ, or T = 1.44 T½

    Units of Radioactivity

    • Curie (Ci) = 3.7 × 10¹⁰ disintegrations/sec
    • Becquerel (Bq) = 1 disintegration/sec
    • 1 Ci = 3.7 × 10¹⁰ Bq

    Half-value Layer

    • Half-life is essential to radiologic science and has a parallel in x-ray terminology. Using half-life, you understand the meaning of half-value layer.
    • 3.3 half-lives = 1 tenth life

    Radiopharmaceutical Loss

    • Loss of radiopharmaceutical in a biological system is due to both radioactive decay and biologic elimination.

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