Part A You are using a Geiger counter to measure the activity of a radioactive s

Question

Part A You are using a Geiger counter to measure the activity of a radioactive substance over the course of several minutes. If the reading of 400. counts  has diminished to 100. counts  after 28.8minutes  , what is the half-life of this substance? Express your answer with the appropriate units.  t 1/2 =____________.

Part B An unknown radioactive substance has a half-life of 3.20hours  . If  41.9g   of the substance is currently present, what mass A 0   was present 8.00 hours ago?Express your answer with the appropriate units.  Ao = ___________.

Part C Americium-241 is used in some smoke detectors. It is an alpha emitter with a  half-life of 432 years . How long will it take in years for 35.0%   of an Am-241 sample to decay?  Express your answer with the appropriate units.  t=__________.

Answers need to please be correct for me to give points.

Explanation / Answer

A)

A half-life time is the time that is taken by a radioactive substance to decay to half of it's original weight or value. Then, we get:
400/2 = 200
200/2 = 100

This took 28.8 minutes.

So the half-life time is 28.8/2 = 14.4 minutes.

B)

the opposite of 1/2 is 2 so

8/3.2=2.5 half lives

so 41.9*2^2.5=amount 8 hours ago = 237.022 g

C)

ln2 = k x 432 years
k = 1.6045x10^-3 years^-1
100% - 35% = 65%
ln(100 / 65) = 1.6045x10^-3 x t
t = 268.48 years

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