Radioactive Source: Range and Penetration
HKDSE-level simulation of alpha, beta, gamma through absorbers
Controls
01.0 mm20 mm
1 cm5.0 cm20 cm
2001200 cps3000
Detector Readings
Transmission
100.0%
Expected Rate
1225 cps
Measured Rate
1213 cps
Penetration
High
Low
Medium
High
Legend
Alpha (α): strong ionisation, short range
Beta (β): medium penetration
Gamma (γ): weak ionisation, high penetration
Absorber slab
HKDSE Concept Summary
Alpha (α): very short range in air (a few cm), stopped by paper or skin.
Beta (β): medium range and penetration, reduced by aluminium sheet.
Gamma (γ): no charge, very penetrating, best reduced by thick lead/concrete.
In experiments, subtract background count rate before comparing source intensities.
Model Used in This Simulation
Approximate count model:
$$R \approx R_0\left(\frac{5}{d}\right)^2T_{\text{air}}T_{\text{absorber}} + R_{\text{background}}$$
For beta/gamma absorption we use an exponential trend:
$$T_{\text{absorber}} \approx e^{-\mu x}$$
This is a teaching model, tuned for HKDSE-style qualitative understanding.
Last updated: 2026-04-25