Part 1: A sample of radioactive material is initially found to have an activity
ID: 2109434 • Letter: P
Question
Part 1: A sample of radioactive material is initially found to have an activity of 116 decays/min. After 5 d, 19 h, its activity is measured to be 80 decays/min.Part 2: How long (from the initial time) will it take for the sample to reach an activity level of 14 decays/min?
Part 1: A sample of radioactive material is initially found to have an activity of 116 decays/min. After 5 d, 19 h, its activity is measured to be 80 decays/min.
Part 2: How long (from the initial time) will it take for the sample to reach an activity level of 14 decays/min?
Explanation / Answer
similar problem and 5 star answer:
A sample of radioactive material is initially
found to have an activity of 126 decays/min.
After 2 d, 15 h, its activity is measured to be
87 decays/min.
Calculate the half life
answer:
ln(A/Ao) = -kt
where A is activity at time t, Ao is initial activity and k is decay constant
Ao = 126 decays/min, A = 87 decays/min
t = 2 days 15 hours = 63 hours
ln(87/126) = -k x 63
k = 0.005879 hour-1
Half life = ln(2)/k
= 0.6931/0.005879
= 118 hours = 4 days 22 hours