Radiation absorption by materials identifies emitted types Steps: - Alpha particles are stopped by thin aluminum; beta penetrates aluminum but is stopped by thin lead; gamma penetrates both but is partially absorbed by lead. - Thin aluminum yields 451 counts/s, indicating no alpha only (would be zero) but presence of penetrating radiation (beta or gamma). - Thin lead reduces to 285 counts/s (63% of aluminum reading), showing partial absorption rather than full blockage. - This pattern fits alpha (blocked by aluminum) plus gamma (partially blocked by lead), with no beta (which lead would fully stop, causing larger drop). Why C is correct: - Alpha and gamma: aluminum stops alpha (451 counts = gamma only), lead partially absorbs gamma (reduces to 285), matching data per absorption laws. Why the others are wrong: - A: Alpha and beta—lead would stop beta after aluminum stops alpha, yielding near-zero counts, not 285. - B: Beta and gamma—lead would stop beta while partially absorbing gamma, causing >50% drop, not 37% reduction. - D: Gamma only—aluminum would barely reduce gamma (expect ~451 for both), but lead …