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A sample of sodium-24 with an activity of 12 mCi is used to study the rate of blood flow in the circulatory system. Sodium-24 has a half-life of 15 h.
What is the radioactivity of the sample of sodium-24 after one half-life?
What is the radioactivity of the sample of sodium-24 after 30 h ?
What is the radioactivity of the sample of sodium-24 after three
half-lives?
What is the radioactivity of the sample of sodium-24 after 2.5 days ?
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Write a balanced nuclear equation for the beta decay of each of the following:
25/11 Na
20/8 O
strontium-92
potassium-42
chem hw help please!?
2016-05-12 3:01 am
回答 (1)
2016-05-12 3:09 am
Half-life is the time it takes for the activity to go down to half its value.
When figuring out activities like this, first figure our how many half-lives you have.
In this case, two and a half days is 60 hours and the half life is 15 hours, so it's 60/15 = 4 half-lives.
Its original activity is 12 mCi, so after one half-life (15 hours) its activity is 6 mCi.
Add another 15 hours, and it goes from 6 to 3 mCi.
And another 15 hours, from 3 to 1.5 mCi.
So 12 to 6 to 3 to 1.5 is all you have to do.
Final answer is 1.5 mCi.
When figuring out activities like this, first figure our how many half-lives you have.
In this case, two and a half days is 60 hours and the half life is 15 hours, so it's 60/15 = 4 half-lives.
Its original activity is 12 mCi, so after one half-life (15 hours) its activity is 6 mCi.
Add another 15 hours, and it goes from 6 to 3 mCi.
And another 15 hours, from 3 to 1.5 mCi.
So 12 to 6 to 3 to 1.5 is all you have to do.
Final answer is 1.5 mCi.
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