# Half-life

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#1
In a laboratory experiment, protactinium-234 undergoes radioactive decay by β-emission into
uranium-234.
The table below describes how the mass of uranium-234 present in the sample varies with time from the start of the experiment:
time/min mass of u-234 / mg
0.0 0.0
1.2 8.0
2.4 12.0
3.6 14.0
4.8 15.0
6.0 15.5
7.2 15.7
8.4 15.9
9.6 15.9
10.8 16.0
12.0 16.0

Using the information in the table, approximately what is the half-life of protactinium-234?

A 1.2 minutes
B 2.4 minutes
C 6.0 minutes
D 9.6 minutes
E 10.8 minutes
F 12.0 minutes

It thought it wwas 9.6 as that is the time it takes for u-234 to double in mass? Why is the answer A?
0
7 years ago
#2
(Original post by Peanut247)
In a laboratory experiment, protactinium-234 undergoes radioactive decay by β-emission into
uranium-234.
The table below describes how the mass of uranium-234 present in the sample varies with time from the start of the experiment:
time/min mass of u-234 / mg
0.0 0.0
1.2 8.0
2.4 12.0
3.6 14.0
4.8 15.0 6.0 15.5
7.2 15.7
8.4 15.9
9.6 15.9
10.8 16.0
12.0 16.0

Using the information in the table, approximately what is the half-life of protactinium-234?

A 1.2 minutes
B 2.4 minutes
C 6.0 minutes
D 9.6 minutes
E 10.8 minutes
F 12.0 minutes

It thought it wwas 9.6 as that is the time it takes for u-234 to double in mass? Why is the answer A?
The total mass is 16.0, so half of that is 8.0. It takes 1.2 minutes for the mass of uranium to go from 0 to 8.0.

Half life is the time taken for the original substance to fall to half of it's original value. The results show that the original value for the protactinium must be around 16.0.

8.0 of uranium made implies that 8.0 of protactinium has decayed.
0
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