Answer :
The reading of the Geiger counter for francium after 22 minutes will be 29 cpm.
Determine the number of half-lives
Half-life (t½) = 22 mins
Time (t) = 22 mins
Number of half-lives (n) =?
n = t / t½
n = 22 / 22
n = 1
Determine the amount remaining
Original amount (N₀) = 58 cpm
Number of half-lives (n) = 1
Amount remaining (N) =?
The reading of the Geiger counter after 22 minutes is given as follow:
N = N₀ / 2ⁿ
N = 58 / 2¹
N = 58 / 2
N = 29 cpm
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