Thorium (with half-life T_1/2 = 1.913 yr. and atomic mass 228.0287 u) undergoes

Question

Thorium (with half-life T_1/2 = 1.913 yr. and atomic mass 228.0287 u) undergoes alpha decay and produces radium (atomic mass 224.0202 u) as a daughter nucleus. (Assume the alpha particle has atomic mass 4.002603 u.) What is the decay constant of thorium? (Note that the answer must be in units of hrs^-1.) lambda = What percent of thorium is left after 200 days? The energy released from the decay of 10 g of thorium is used to heat 3.8 kg of water (assume all the energy released goes into the water). What is the change in temperature of the water after 1 hr.?

Explanation / Answer

THe decay constant is given as

Decay constant = ln(2)/t1/2 = 0.693/1.913 = 0.362 hrs-1

The percentage of ions left = 100 * (1/2)(200/1.913*365) = 82%

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