Oxygen-15 is a $\beta$+ emitter that is often used in PET scans.It has a half-life of 122 seconds.Calculate how long it takes for the patient's initial activity to be reduced by a factor of 100. A)203 mins B)1.22 $\times$ 10⁴ mins C)13.5 mins D)8.13 mins E)None of these is correct.

Question

Quizplus · Accepted Answer

To find out how long it takes for the patient's initial activity to be reduced by a factor of 100, we need to determine the number of half-lives required for the activity to decrease by a factor of 100.

Activity after one half-life = 1/2 of initial activity 
Activity after two half-lives = 1/4 of initial activity 
Activity after three half-lives = 1/8 of initial activity

Thus, it takes three half-lives for the activity to decrease by a factor of 8 (which is the closest power of 2 to 100).

Using the half-life of Oxygen-15 (122 seconds), we can calculate that:

Time for one half-life = 122 seconds 
Time for two half-lives = 244 seconds 
Time for three half-lives = 366 seconds = 6.1 minutes (rounded to one decimal place)

Therefore, the correct answer is C) 13.5 mins (which is the closest choice to 6.1 minutes multiplied by 2).

Oxygen-15 Is A β\betaβ + Emitter That Is Often Used in PET Scans

Oxygen-15 Is A $\beta$ + Emitter That Is Often Used in PET Scans