1. Suppose a medical PET scan uses an isotope that has a half-life of 1.5 hr. A

Question

1. Suppose a medical PET scan uses an isotope that has a half-life of 1.5 hr. A sample prepared at 10:00 A.M. has an activity of 30 mCi. What is the activity at 1:00 P.M., when the patient is injected?
____________ mCi

3.A slab of material of thickness 3.0 cm reduces the amount of radiation by a factor of 5.0. How much is the radiation reduced (from its original amount) if you use a 9.0cm thickness of this material? (Answer by the factor by which it's reduced, so your answer should be > 1; e.g., if it's cut in 1/2, you would answer 2. ____________

Explanation / Answer

1)  Time interval 3hours
Half life 1.5 hr 1/2
after 3.0 hr 1/4
30mCi /4= 7.5 mCi

2) Rate constant lambda = Q'/Q = 4.1E8/5.5E15 = 0.75E-7 /s
half-life = ln(2)/lambda s = ln(2)/(lambda*86400) = 106.97 days

3) As thickness increase 3 times , then radiation reduces 9 times i.e. 45 times from its original amount.

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