A half-value layer is a shielding step that cuts an ideal count rate in half. The visible chain here applies three exact halves, taking 64 counts per second to 32, then 16, then 8 counts per second. Real shielding depends on radiation type, material, spectrum, geometry, detector response, background subtraction, and counting uncertainty.
Half-value layers are exact repeated halvings. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
Each half-value layer halves the count rate
3 exact half-value layers turn 64 per second into 8 per second.