Nuclear PE

On the PE exam, you'll often need to calculate the number of atoms N from given mass using N = (mass × Avogadro's number) / atomic mass. The decay constant λ is related to half-life by λ = ln(2)/t₁/₂. Remember that 1 Ci = 3.7×10¹⁰ Bq exactly.

This is the fundamental heat balance equation for reactor power. PE exam problems often give flow rate and temperatures, asking for power, or vice versa. Remember that cp varies significantly with temperature for pressurized water - use appropriate values from steam tables, not room temperature water properties.

The four-factor formula is fundamental for thermal reactor analysis. Remember η depends on fuel enrichment, f on fuel-to-moderator ratio, p on resonance absorption, and ε on fast fission. For finite reactors, multiply by non-leakage probability to get keff.

Know common gamma constants for Co-60, Cs-137, and Ir-192. Remember this is an approximation - buildup factors may be needed for thick shielding. Distance is measured from source center, not surface. The 1/r² relationship means doubling distance reduces dose rate by factor of 4.

Always verify units match - if given half-life in years, convert to seconds for λ calculation, or convert final answer back to appropriate time units. Remember λ has units of 1/time, so larger λ means shorter half-life.