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Chapter 42: Q 19 Exercise (page 1236)

The radium isotope 226Ra has a half-life of 1600 years. A

sample begins with 1.00x1010 226Ra atoms. How many are left

after (a) 200 years, (b) 2000 years, and (c) 20,000 years?

Short Answer

Expert verified

Therefore,

a.)N=9.17×109atomsb.)N=4.20×109atomsc.)N=1.73×106atoms

Step by step solution

01

Given information

t1/2=1600yearsNo=1.0×1010atoms

02

Explanation (a)

(a)After t = 200 years, we must determine the number of nuclei 226Ra that remain.

N=No12t/t1/2N=1.0×1010atoms12200years/1600yearsN=1.0×1010atoms120.125N=1.0×1010atoms×(0.9170)N=9.17×109atoms

03

Explanation (b)

(b)After t = 2000 years, we must determine the number of nuclei 226Ra that remain.

N=No12t/t1/2N=1.0×1010atoms122000years/1600yearsN=1.0×1010atoms12125N=1.0×1010atoms×(0.42044)N=4.20×109atoms

04

Explanation (c)

(c)After t = 20000 years, we must determine the number of nuclei 226Ra that remain.

N=No12t/t1/2N=1.0×1010atoms1220000years/1600yearsN=1.0×1010atoms1212.5N=1.0×1010atoms×(0.00017)N=1.73×106atoms

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