Physics - Review Answer 191

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191.	Promethium-61 has a half-life of 17.7 years. How long must a sample be stored for the radioactivity to drop to 1/32 its original amount?
	A.	17.7 years	The half-life is the time necessary for half of the atoms to decay. Assume 1 kg ⁶¹Pm at time 0 1/2 kg at 17.7 years 1/4 kg at 35.4 years 1/8 kg at 70.8 years 1/16 kg at 88.5 years 1/32 kg at 106 years The Correct Answer is D.
	B.	70.8 years
	C.	88.5 years
	D.	106 years