DECK 7 — BETA & GAMMA ATTENUATION

What is gamma-ray attenuation?

Gamma-ray attenuation is the reduction in photon intensity as gamma rays pass through matter.

What equation describes gamma-ray attenuation?

The equation I = I0 · e^(−μx) describes gamma-ray attenuation.

What is the linear attenuation coefficient μ?

The linear attenuation coefficient μ quantifies the probability of photon interaction per unit thickness.

What is the mass attenuation coefficient μ/ρ?

The mass attenuation coefficient μ/ρ removes density dependence and allows material comparison.

What does a larger attenuation coefficient indicate?

A larger coefficient indicates more interactions and stronger attenuation.

What determines the attenuation coefficient for gamma rays?

Gamma energy and atomic number of the absorber determine the attenuation coefficient.

What is a half-value layer (HVL)?

HVL is the thickness of material needed to reduce gamma intensity to one half.

What is a tenth-value layer (TVL)?

TVL is the thickness needed to reduce gamma intensity to one tenth.

How is HVL related to μ?

HVL = ln(2)/μ.

How is TVL related to μ?

TVL = ln(10)/μ.

Why does the HVL change with photon energy?

Photon interaction probabilities vary with energy, changing attenuation behavior.

Why do high-Z materials attenuate gamma rays more effectively?

High-Z materials increase photoelectric and pair-production probabilities.

Why does the photoelectric effect dominate at low gamma energies?

Photoelectric probability increases sharply as photon energy decreases.

Why does Compton scattering dominate at intermediate energies?

Compton scattering has weak Z dependence and occurs across many materials.

Why does pair production dominate at high gamma energies?

Pair production requires photon energies above 1.022 MeV and increases with energy.

Why is buildup sometimes observed in gamma attenuation experiments?

Scattered photons may still reach the detector, increasing measured intensity.

Why does gamma attenuation deviate from pure exponential at small distances?

Geometry, scattering, and source-detector alignment distort simple exponential behavior.

What is beta attenuation?

Beta attenuation is the reduction of beta particle intensity through energy loss and scattering in matter.

Why do beta particles not follow exponential attenuation?

Beta particles undergo continuous energy loss and scattering rather than discrete interactions.

Why do beta particles have a maximum range?

Beta particles stop when they lose all kinetic energy through collisions.

What determines the range of beta particles?

Initial energy, material density, and atomic number determine beta range.

What is the continuous slowing down approximation (CSDA) range?

CSDA range is the average distance a beta particle travels before coming to rest.

Why do beta particles produce bremsstrahlung in absorbers?

Beta particles decelerate in electric fields of nuclei and emit bremsstrahlung photons.

Why should beta radiation be shielded with low-Z materials?

Low-Z materials reduce bremsstrahlung production compared to high-Z materials.

Why does bremsstrahlung become significant for high-energy betas?

Higher beta energies cause stronger deceleration and more photon production.

How is beta shielding different from gamma shielding?

Beta shielding uses low-Z materials to avoid bremsstrahlung, while gamma shielding uses high-Z materials.

What effect does absorber thickness have on beta count rate?

Count rate decreases until beta particles are fully stopped, then levels off.

Why might gamma background appear in a beta attenuation experiment?

Bremsstrahlung and source gamma emissions may be detected.

How is the linear attenuation coefficient experimentally determined?

Plot ln(I) vs thickness and use the slope equal to −μ.

Why is detector alignment important in attenuation experiments?

Misalignment changes geometric efficiency and distorts attenuation results.

Why are narrow-beam conditions preferred for gamma attenuation measurements?

Narrow-beam geometry minimizes scattering contributions to the detector.

Why does scattering complicate attenuation measurements?

Scattered photons may still reach the detector, causing non-exponential behavior.