An isotope has a 12.4 hrs half-life. If it has an activity of 30mCi at noon today, what was its activity at 3 pm yesterday?
What is JNV? This looks like a chemistry question to me. JNV must be an interesting subject, though (I guess).
To determine the activity of the isotope at 3 pm yesterday, we need to calculate how much of the isotope decayed during that time period.
First, we need to find out how many half-lives have passed between 3 pm yesterday and noon today. The time difference between 3 pm yesterday and noon today is 21 hours (from 3 pm to midnight is 21 hours, and from midnight to noon is another 12 hours, giving a total of 33 hours).
Next, we can use the half-life of the isotope to calculate the number of half-lives that have passed. The half-life of the isotope is 12.4 hours. Dividing the total time difference of 21 hours by the half-life of 12.4 hours will give us the number of half-lives.
Number of half-lives = (Total time difference) / (Half-life)
= 21 hours / 12.4 hours
≈ 1.69
Since we can't have a fraction of a half-life, we round down to the nearest whole number.
Number of half-lives = 1
Now, to calculate the activity at 3 pm yesterday, we need to multiply the initial activity (30 mCi) by the fraction remaining after one half-life.
After one half-life, the remaining fraction of the isotope is (1/2) or 0.5. Therefore, the activity at 3 pm yesterday can be calculated as:
Activity at 3 pm yesterday = Initial activity x Remaining fraction after one half-life
= 30 mCi x 0.5
= 15 mCi
Therefore, the activity of the isotope at 3 pm yesterday was approximately 15 mCi.