   Chapter 31, Problem 56PE

Chapter
Section
Textbook Problem

Data from the appendices and the periodic table may be needed for these problems.A 5000−Ci 60Co source used for cancer therapy is considered too weak to be useful when its activity falls to 3500 Ci. How long after its manufacture does this happen?

To determine

To time taken to fall the activity of C60o .

Explanation

Given info:

• The initial activity of C60o is 5000Ci .
• The final activity of C60o is 3500Ci .

The half-life of K40 is 5.271y .

Formula used:

Formula to find the activity is,

Initial activity is,

Ri=0.693Nit12

Equation-1

Final activity is,

Rf=0.693Nft12

Equation-2

Here, Ni is the initial number of C60o , Nf is the present number of atom, t12 is the half-life of C60o and t is the time elapsed, Rf is the present activity and Ri is the initial activity.

The radioactivity decay equation is,

NfNi=e0

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