Physics College

Cobalt-60 (Co) is often used as a radiation source in medicine. It has a half-life of 5.25 years. 4.1. Explain what is meant by the underlined sections in the statement above. [5] Using her knowledge and understanding of nuclear physics, a student was asked to answer the following problem about cobalt-60: How long after a new sample is delivered will its activity have decreased (a) to about one-eighth its original value? (b) to about one-third its original value? Give your answers to two significant figures. The student was also provided with the following information: The activity is proportional to the number of undecayed atoms (AN/At = AN) 4.2. Explain what is meant by the information above provided to the student. [5]​

Answers

Answer 1

From the question;

1) It takes 15.75 years to decrease to 1/8

2) It takes 8.36 years to decrease to 1/3

What is half life?

Half-life is the length of time it takes for a chemical to degrade or go through a particular process. It frequently refers to the length of time it takes for half of a radioactive substance to decay into a stable form in the context of radioactive decay.

We know that;

[tex]N/No = (1/2)^t/t1/2[/tex]

No = initial amount

N = amount at time t

t = Time taken

t1/2 = half life

[tex]1/8 = (1/2)^t/5.252^-3 = 2^-t/5.25[/tex]

t = 15.75 years

Again;

[tex]1/3 = (1/2)^t/5.25[/tex]

ln0.33 = t/5.25ln0.5

t = ln0.33/ln0.5 * 5.25

t = 8.36 years

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