Chapter 21: Radioactivity and Nuclear Chemistry

Positron Emission Tomography (PET) and Radioactivity

• PET (Positron Emission Tomography) is a medical imaging technique that involves the emission of positrons.

• Individuals undergoing a PET scan are injected with contrast agents that enhance imaging signals.

• Certain injectable compounds, such as radioactive antibodies, target infections directly and aggregate at sites of infection, allowing visualization through various scanning techniques.

• Knowledge of radiochemistry and nuclear chemistry is essential for medical professionals involved in the use of PET scans.

Principles of Radioactivity

• Definition of Radioactivity: The emission of particles from atomic nuclei, where these particles are typically subatomic and possess high energy.

• Types of particles emitted:
    - Different particles exhibit varying energy levels and health hazards.
    - Understanding the protection measures against these particles is crucial.

Radioactive Decay

• Overview of different forms of radioactive decay, emphasizing identification and nuclear equations.

• Atomic Number and Mass:
    - The atomic number represents the number of protons.
    - The mass number is the total count of protons and neutrons.
    - To find neutrons:
      - ${Neutrons}={Mass Number}-{Atomic Number}$

• Isotopes: Atoms of the same element with different neutron counts.

Notation for subatomic particles

Proton Symbol: $_1^1$ P

Neutron Symbol: $_0^1$ n

Electron Symbol: $_{-1}^0$ e

Types of Radioactive Decay

Alpha Decay

• Definition: Emission of alpha particles, equivalent to helium nuclei (2 protons and 2 neutrons).

• Transformation:
    - Changes the original element due to loss of protons.
    - Example: Uranium-238 decaying to Thorium-234 via alpha emission.
    - Nuclear equation for alpha decay:
      - $_{92}^{238}{U}\rightarrow{_2^4He}+{}_{90}^{234}{Th}$

parent nuclide daughter nuclide

• A nuclear equation must be balanced with respect to atomic numbers and mass numbers:

Penetration and Safety:

• Largest radioactive particle

• Alpha particles are highly ionizing but poorly penetrating; a sheet of paper can block them.

• Dangerous if ingested or inhaled.

Beta Decay

In some unstable nuclei, a neutron changes into a proton and emits an electron

• Definition: Transformation of a neutron into a proton while emitting an electron (beta particle).

Electron Emission:
  - The neutron converts, yielding an increase in protons.
  - Example: Carbon-14 undergoing beta decay.
  - Nuclear equation for beta decay:
$_6^{14}C\rightarrow_7^{14}C+_{-1}^0e$

• Penetration and Safety:
  Less massive than alpha particles

• Beta particles are lower ionizing but higly penetrating; precautions involve metal shielding.

• Consumption of beta emitters less damaging than alpha emitter

Gamma Decay

• Definition: A form of electromagnetic radiation with no mass and high energy (short wavelength) photons

• Connection to Decay: Usually emitted from nuclei in conjunction with other types of radiation

• Gamma Nuclear symbol: $_0^0\gamma$

• Penetration and Safety:
    - Lowest ionizing power yet high penetration; requires thick shielding (e.g., lead/concrete).

Positron Emission

• Definition: Emission of positrons, the antiparticle of electrons from unstable nuclei.

• Transformation of Particles:
    - A proton transforms into a neutron while emitting a positron; proton $\rightarrow$ neutron + emitted positron

• When an atom emits a positron, its atomic number decreases by 1 because it has one less proton after emission, however top number (atomic mass which is the neutrons + protons) stays the same as one simply swaps for another

• Positron Nuclear symbol: $_{+1}^0e$

• Example: $_6^{10}C\rightarrow_5^{10}C+_{+1}^0e$

Electron Capture

Electron capture involves a particle being absorbed by rather than emitted from an unstable nucleus

• Definition: An atom captures an inner-shell electron and converts a proton into a neutron.

• Proton + electron $\rightarrow$ neutron

• The atomic number decreases by 1 because it has one less proton

• Nuclear Equation: $_1^1P+_{-1}^0e\rightarrow_0^1n$

• Example:
    - From an element going into another element with decreased atomic number.
    - $_{44}^{99}Ru+_{-1}^0e^{}\rightarrow{}_{43}^{99}Tc$

Nuclear Decay Chart