CAIE IGCSE Physics 5.2.4.1 Half Life As the Time for Half the Questions

Learn to count elapsed half-lives, calculate decay quantities and remove background count before applying radioactive decay.

Exam points

determine the number of half-lives elapsed from time and half-life
calculate remaining or decayed mass, activity or nuclei after repeated half-lives
correct detector readings for background count before applying radioactive decay

[Maximum number: 3]

A source contains a radioactive isotope of strontium. This isotope decays by emission of $\beta$ -particles. The half-life of this isotope is 29 years.

The initial mass of this isotope of strontium in the source is $25 \mu \mathrm{~g}$ .

Calculate the mass of the strontium isotope that decays in 87 years.

$22 \mu \mathrm{~g}$
(87 years is) three half-lives OR 25 / 8 OR 87 / 29=3 (half lives)
1/8th (of the strontium remains) OR 25 / 8 (decays) OR 3.125 seen

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CAIE IGCSE Physics 5.2.4.1 Half Life As the Time for Half the Questions question 1