Iodine-125 (125I) is used to treat, among other things, brain tumors and prostat

Question

Iodine-125 (125I) is used to treat, among other things, brain tumors and prostate cancer. It decays by gamma decay with a half-life of 54.90 days. Patients who fly soon after receiving 125I implants are given medical statements from the hospital verifying such treatment because their radiation could set off radiation detectors at airports. If the initial decay rate (or activity) was 532 ?Ci, what will the rate be after 365.0 days?

lodine-125 (25) is used to treat, among other things, brain tumors and prostate cancer. It decays by gamma decay with a half-life of 54.90 days. Patients who fly soon after receiving 125l implants are given medical statements from the hospital verifying such treatment because their radiation could set off radiation detectors at airports. If the initial decay rate (or activity) was 532 Ci, what will the rate be after 365.0 days? Number How many months after the treatment will the decay rate be reduced to 16.5% of the original value? Assume months of 30 days. Number months

Explanation / Answer

N(t) = N0 * e^-t*K
K = decay constant = 0.693/t1/2
K = 0.693/54.9
K = 0.0126
N(t) = 532 * e^-(365*0.0126)
N(t) = 5.353 micro Ci

N(t) = N0 * e^-t*K
532 * 16.5/100 = 532 * e^(-t*0.0126)
t = 143 days
t = 143/30 = 4.767 months

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