   Chapter 31, Problem 50PE

Chapter
Section
Textbook Problem

Data from the appendices and the periodic table may be needed for these problems.(a) Natural potassium contains 40K, which has a half−life of 1.277 × 10 9 y . What mass of 40K in a person would have a decay rate of 4140 Bq? (b) What is the fraction of 40K in natural potassium, given that the person has 140 g in his body? (These numbers are typical for a 70−kg adult.)

To determine

(a)

What mass of 40K have a decay rate of 4140Bq .

Explanation

Given info:

The half-life of 40K is 1.277×109y .

Convert years in to seconds.

1.277×109y=1.277×109y×3.155×107s1y=4.03×1016s

The activity of 40K is 4140Bq .

Formula used:

To find the mass first we need to find the number of atoms involved to produce this activity.

N(40K)=R×t120

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