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# Physics (Nuclear)

23) (ex) Some &quot;Exit&quot; signs glow in the dark because of the beta decay of hydrogen-3 ( , H ), also called
tritium because of its three nucleons. (a) The initial mass of tritium in these signs is a safely small
3.00x10 g. How many atoms of tritium (neutral atomic mass 3.016049 u) is this? (b) The half-life
of tritium is 12.3 years. What is the initial activity of the tritium? (c) With time, the activity drops,
leading to a dimmer sign that eventually needs to be replaced. If the minimum activity (for a bright
enough sign) is 9.00x10&quot; Ci, after how many years should a sign be replaced?

The way to approach this... View the full answer

a . lu 2 1 6 6 X 1 0 27 up
- 1-68 X 10 -27
x10 9
18 = 10-3 kg
7 18 = 1:68 *10-24 4
- 6 ' 024 x 1023 4
Now, mass of tritium, m = 3x109
= 1 . 80 7 x 10 18 2
Neutral atomic mass of any atom contains...

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