a radiation lab produces 64mg of 220Fr.The lab need just 2 mg for the experiment.how long do they need to?

Question

transport the isotope and still have enough

Answer 1

I looked up the half-life of 220 Fr ( http://nucleardata.nuclear.lu.se/nucleardata/toi/listnuc.asp?sql=&Z=87 ). It is 27.4 sec.

64 mg will decay down to 2 mg in 5 half-lives:
64 => 0
32 => 1 half life
16 => 2 half lives
8 => 3 half lives
4 => 4 half lives
2 => 5 half lives

5 half-lives * 27.4 sec per half-life = 137 sec, or slightly more than 2 minutes. They had better hurry!

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Answer 2

I presume you have been told the half life. Without such information, there is obviously no way to solve the problem.

After one half life they will have 32 mg, after two half lives only 16, ...

Take it from there.