   Chapter 31, Problem 58PE

Chapter
Section
Textbook Problem

Data from the appendices and the periodic table may be needed for these problems.58. The β − particles emitted in the decay of 3H (tritium) interact with matter to create light in a glow−in−the−dark exit sign. At the time of manufacture, such a sign contains 15.0 Ci at 3H. (a) What is the mass at the tritium? (b) What is its activity 5.00 y after manufacture?

To determine

(a)

The mass of the tritium sample.

Explanation

Given info:

The half-life of tritium is 12.33y .

The atomic mass of tritium is 5.0082×1027kg .

Formula used:

Find the mass of tritium:

Writing the formula of activity R in term of atomic mass M and mass of sample m and half-life t12 ,

R=0.693×Nt 1 2R=0.693×mMt 1 2

Rearrange the formula to find the expression for m ,

R=0.693× m M t 1 2 m=Rt 1 2M0.693 Equation-1

Calculation:

Find the mass of sample substitute all known values in equation-1

m=15Ci×12.33y×5.0082×1027kg0

To determine

(b)

The activity of tritium after 5y .

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