Ionising Radiation & Detectors

Gas Ionization: When radiation passes through a gas-filled chamber, it strikes gas atoms, stripping electrons and creating positive ions. If an electric field is applied, these charges migrate to electrodes, creating a measurable current.

Excitation and Fluorescence: In certain materials called scintillators, radiation energy excites electrons to higher energy levels. When these electrons return to their ground state, they emit flashes of light (photons) proportional to the radiation energy.

Electron-Hole Pair Production: In semiconductor detectors, radiation creates charge carriers (electrons and holes) in the solid-state lattice. This is analogous to gas ionization but occurs in a much denser medium, allowing for higher sensitivity and energy resolution.

Inverse Square Law: For a point source of gamma radiation, the intensity ($I$) decreases with the square of the distance ($d$) from the source, expressed as $I \propto \frac{1}{d^2}$.

Correcting for Background: Always subtract the background count rate from the total measured count rate before performing calculations like half-life or inverse square law. $Corrected\ Rate = Total\ Rate - Background\ Rate$

Unit Precision: Distinguish between Absorbed Dose (Gray, $Gy = J/kg$) and Equivalent Dose (Sievert, $Sv$). The Sievert accounts for the biological effectiveness of different radiation types ($Sv = Gy \times Quality\ Factor$).

Safety Calculations: When distance is doubled, the radiation intensity drops to one-quarter ($1/2^2$). If distance is tripled, it drops to one-ninth ($1/3^2$). Always check if the distance is measured from the center of the source.

Sanity Check: If a problem involves shielding, remember that $\alpha$ cannot pass through even a few centimeters of air or a sheet of paper. If a detector still clicks behind paper, the source is not purely $\alpha$.