Answer :
When the experiment begins after 10 minutes, approximately 20 grams of barium-122 will be left from the initial 80-gram sample.
The half-life of a radioactive substance is the time it takes for half of the sample to decay. In this case, barium-122 has a half-life of 5 minutes. This means that after every 5 minutes, the amount of barium-122 is halved.
Given that it takes 10 minutes to set up the experiment, we need to determine how much barium-122 will remain at that point. Since the half-life of barium-122 is 5 minutes, we can calculate the number of half-lives that have passed in 10 minutes, which is 2 half-lives (10 minutes / 5 minutes per half-life).
Each half-life halves the amount of barium-122, so after 2 half-lives, we are left with 1/4 (1/2 * 1/2) of the original amount. Therefore, 1/4 of the 80-gram sample remains, which is 20 grams.
Hence, when the experiment begins after 10 minutes, approximately 20 grams of barium-122 will be left from the initial 80-gram sample.
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