1 . Answer the following questions about 2 3 8 U and 2 3 4 Th activities in a body of water in the surface ocean with salinity S = 3 4 . 0 . Assume that U is present in seawater as a conservative ion. The decay constant of 2 3 8 U is 1 . 5 5 \ times 1 0 1 0 yr 1 . The concentration of 2 3 8 U is 1 3 . 1 1 nmol / kg .

a . Calculate the activity of 238U ( A238) in this seawater in units of dpm / kg ( disintegrations per minute per kilogram of seawater ) .

b . What is the activity of 234Th ( A234) in this seawater if 238U and 234Th are in secular equilibrium? Please report your answer in units of dpm / kg .

c . The activity of 234Th ( A234) in this body of seawater is 0.6 6 dpm / kg . Assuming that radioactive decay and scavenging by sinking particles are the only mechanisms that remove ²³⁴Th from this water, and that ²³⁴Th activity is in steady-state, calculate the scavenging rate constant, k, for ²³⁴Th. Report your answer in units of day^-1.